Maharashtra Board Class 11 Biology Chapter 16 Skeleton and Movement Solutions

1. Choose the Correct Option

 

Question (A). The functional unit of striated muscle is .............
(a) cross bridges
(b) myofibril
(c) sarcomere
(d) z-band
Answer: (c) sarcomere
In simple words: A sarcomere is the basic microscopic unit of a muscle that contracts and relaxes, allowing our muscles to move.

🎯 Exam Tip: Remember that sarcomeres are the repeating structural units located between two Z-lines in striated muscle fibers.

 

Question (B). A person slips from the staircase and breaks his ankle bone. Which bones are involved?
(a) Carpals
(b) Tarsal
(c) Metacarpals
(d) Metatarsals
Answer: (b) Tarsal
In simple words: Tarsal bones are the group of bones that make up our ankle, so breaking an ankle bone means injuring a tarsal bone.

🎯 Exam Tip: Do not confuse carpals (wrist bones) with tarsals (ankle bones). A simple trick is to associate 'T' in Tarsals with Toes/feet.

 

Question (C). Muscle fatigue is due to accumulation of ........
(a) pyruvic acid
(b) lactic acid
(c) malic acid
(d) succinic acid
Answer: (b) lactic acid
In simple words: When muscles work very hard without enough oxygen, they produce lactic acid, which builds up and makes them feel tired and sore.

🎯 Exam Tip: Muscle fatigue is caused by anaerobic respiration, which converts glucose into lactic acid when oxygen supply is low.

 

Question (D). Which one of the following is NOT antagonistic muscle pair?
(a) Flexo-extensor
(b) Adductor-abductor
(c) Levator-depressor
(d) Sphinetro-suprinater
Answer: (d) Sphinetro-suprinater
In simple words: Antagonistic muscles work in opposite pairs, like one bending a joint and the other straightening it. Sphincter and supinator muscles do not work as an opposing pair.

🎯 Exam Tip: Remember the common antagonistic pairs like flexor-extensor and abductor-adductor to easily eliminate incorrect options in exams.

 

Question (E). Swelling of sprained foot is reduced by soaking in hot water containing a large amount of common salt,
(a) due to osmosis
(b) due to plasmolysis
(c) due to electrolysis
(d) due to photolysis
Answer: (a) due to osmosis
In simple words: The high salt concentration outside the skin draws excess water out of the swollen cells through a semi-permeable membrane, reducing the swelling.

🎯 Exam Tip: Always associate the movement of water from low solute concentration (inside cells) to high solute concentration (saltwater) with osmosis.

 

Question (F). Role of calcium in muscle contraction is ..........
(a) to break the cross bridges as a cofactor in the hydrolysis of ATP
(b) to bind with troponin, changing its shape so that the actin filament is exposed
(c) to transmit the action potential across the neuromuscular junction.
(d) to re-establish the polarisation of the plasma membrane following an action potential
Answer: (b) to bind with troponin, changing its shape so that the actin filament is exposed
In simple words: Calcium acts like a key that unlocks the muscle fibers, allowing them to bind together and pull to make the muscle contract.

🎯 Exam Tip: Focus on the calcium-troponin-tropomyosin complex interaction as it is a highly tested mechanism in muscle physiology.

 

Question (G). Hyper-secretion of parathormone can cause which of the following disorders?
(a) Gout
(b) Rheumatoid arthritis
(c) Osteoporosis
(d) Gull’s disease
Answer: (c) Osteoporosis
In simple words: Too much parathormone causes the body to take too much calcium out of the bones, making them weak, brittle, and easily breakable.

🎯 Exam Tip: Associate parathormone (PTH) with bone demineralization; hyper-secretion directly leads to weak bones or osteoporosis.

 

Question (H). Select correct option between two nasal bones
(a) Squamous suture
(b) Denticulate suture
(c) Plane suture
(d) Serrate suture
Answer: (c) Plane suture
In simple words: The two nasal bones meet in the middle at a flat, straight line called a plane suture, which joins them securely without overlapping.

🎯 Exam Tip: Remember that plane sutures (harmonic sutures) occur where flat bones meet edge-to-edge, such as between the nasal bones.

 

Answer the Following Questions

 

Question (A). What kind of contraction occurs in your neck muscles while you are reading your class assignment?
Answer:
1. Isometric contractions occur in the neck muscles while reading class assignment.
2. These contractions are important for supporting objects in a fixed position. This steady muscle tension keeps the head upright and stable without causing any actual movement of the joint.
In simple words: When you read, your neck muscles stay tight to hold your head steady without moving it. This is called an isometric contraction.

🎯 Exam Tip: Clearly distinguish between isometric (same length, no movement) and isotonic (change in length, active movement) contractions to score full marks.

 

Question (B). Observe the diagram and enlist importance of ‘A’, ‘B’ and ‘C’.

• A: Facet for odontoid process (Anterior arch)
• B: Vertebral foramen (Neural canal)
• C: Transverse foramen (Foramen transversarium)

Answer:
1. Importance of 'A' (Facet for odontoid process / Anterior arch): It articulates with the odontoid process (dens) of the axis vertebra to form a pivot joint. This joint allows the head to rotate from side to side, as when shaking the head to say "no".
2. Importance of 'B' (Vertebral foramen / Neural canal): It is a large central opening that houses and protects the delicate spinal cord as it passes down from the brain.
3. Importance of 'C' (Transverse foramen): These openings in the transverse processes allow the vertebral arteries, veins, and nerves to safely pass upward to supply the brain. This unique anatomical arrangement ensures that vital blood vessels are well-protected during neck movements.
In simple words: 'A' forms a joint that lets you turn your head, 'B' is the main tunnel protecting your spinal cord, and 'C' is a side pathway for blood vessels going to your brain.

🎯 Exam Tip: When describing anatomical diagrams, always identify the structure first (e.g., Atlas vertebra) before explaining the functions of its labeled parts.

 

Question (C). Raju intends to train biceps; while exercising using dumbbells, which joints should remain stationary and which should move?
Answer: While performing exercise of biceps using dumbbells, the joint which should remain stationary are wrist joint or radiocarpal joint, ball and socket joint of shoulder. The only joint which should move is hinge joint of elbow. This selective movement ensures that the target muscle group is effectively isolated and worked.
In simple words: When doing bicep curls, you should only bend your elbow. Keeping your shoulder and wrist still helps focus all the work on your biceps.

🎯 Exam Tip: Clearly distinguish between the stationary joints (shoulder and wrist) and the moving joint (elbow) to score full marks.

 

Question (D). In a road accident, Moses fractured his leg. One of the passers by, tied a wodden plank to the fractured leg while Moses was rushed to the hospital Was this essential? Why?
Answer:
1. Fracture is a significant and traumatic injury which requires medical attention however, getting timely first aid is important.
2. If any bone is fractured, it is essential that the fractured part be immobilized to prevent further injury. It can be done with the help of any available wooden plank or batons or rulers. Thus, a wooden plank was tied to Moses’s fractured leg as a first aid for fracture.
3. A fractured bone is immobilized to prevent the sharp edges of the fractured bone from moving and cutting tissue, muscle, blood vessels and nerves. Immobilization can also help reduce pain or control shock. This simple act of first aid can prevent temporary damage from becoming a permanent disability.
In simple words: Yes, tying a wooden plank was very important. It keeps the broken leg still so the sharp bone ends do not move around and cut internal tissues or blood vessels on the way to the hospital.

🎯 Exam Tip: Mention "immobilization" as the key term and explain how it prevents further internal damage to blood vessels and nerves.

 

Question (E). Sprain is more painful than fracture. Why?
Answer:
1. A sprain is an injury that involves the ligaments (tissues that connect bones at joints), whereas a fracture is an injury that involves bones.
2. Ligaments have a rich supply of sensory nerve endings which are highly sensitive to stretch and pain.
3. Therefore, any stretching or tearing of ligaments in a sprain sends intense pain signals to the brain, making it extremely painful compared to some bone fractures. Additionally, the swelling and inflammation around the joint further compress these sensitive nerve endings.
In simple words: A sprain hurts more because ligaments have many more sensitive pain receptors than bones. When these ligaments stretch or tear, they send very strong pain signals to the brain.

🎯 Exam Tip: Highlight the presence of rich sensory nerve supply in ligaments compared to bones to explain the intensity of pain.

 

Question (F). Why a red muscle can work for a prolonged period whereas white muscle fibre suffers from fatigue after a shorter work? (Refer to chapter animal tissues.)
Answer:
1. Red muscle fibres contain large amount of myoglobin and mitochondria (site of aerobic respiration), whereas white muscles fibres contain lesser amount of myoglobin and mitochondria.
2. Myoglobin is an iron-containing pigment that carries oxygen molecules to muscle tissues. Abundance of these pigments in red muscle fibres supports higher rate of aerobic respiration, whereas white muscle fibres have less mitochondria and depend upon anaerobic respiration. This oxygen-storing capability allows red muscles to sustain activity for much longer periods.
3. Anaerobic respiration in muscle white fibres leads to the production of lactic acid and accumulation of higher of levels lactic acid can result in fatigue in white muscle fibres.
Thus, red muscle fibres can perform prolonged work and show less fatigue due to accumulation of negligible amount of lactic acid, whereas white muscle fibres fatigue quickly.
In simple words: Red muscles have plenty of oxygen and energy-producing mitochondria, allowing them to work for a long time. White muscles have less oxygen and produce lactic acid, which makes them tire out very quickly.

🎯 Exam Tip: Clearly highlight the role of myoglobin and mitochondria in aerobic respiration to secure full marks in comparative muscle questions.

Answer the Following Questions in Detail

 

Question (A). How is the structure of sarcomere suitable for the contractility of the muscle? Explain its function according to sliding filament theory. (Refer to chapter animal tissues.)
Answer:
i. Sarcomere is the functional unit of myofibril. It has specific arrangement of actin and myosin filaments. The components of sarcomere are organized into variety of bands and zones. Actin and myosin are referred as contractile proteins. Actin is called as thin filament whereas myosin in called as thick filament. This structural organization allows the muscle to generate force efficiently during contraction. The structure of sarcomere:
ii. ‘A’ band – dark bands present at the centre of sarcomere and contain myosin as well as actin.
‘H’ zone or Hensen’s zone – light area present at the centre of ‘A’ band
‘M’ line – present at the centre of ‘H’ zone
‘I’ band – light bands present on the either side of ‘A’ band containing only actin
Z’ line – adjacent ‘I’ bands are separated by ‘Z’ line.
iii. Sliding filament theory: It was put forth by H.E Huxley and A.F Huxley. It is also known as ‘Walk along theory’ or Ratchet theory.

• According to the sliding filament theory, the interaction between actin and myosin filaments is the basic cause of muscle contraction. The actin filaments are interdigitated with myosin filaments.
• The head of the myosin is joined to the actin backbone by a cross bridge forming a hinge joint. From this joint, myosin head cannot tilt forward or backward. This movement is an active process as it utilizes ATP.
• Myosin head contains ATPase activity. It can derive energy by the breakdown of ATP molecule. This energy can be used for the movement of myosin head.
• During contraction, the myosin head gets attached to the active site of actin filaments and pull them inwardly so that the actin filaments slide over the myosin filaments.

In simple words: A sarcomere is the basic unit that makes muscles contract, containing overlapping thin (actin) and thick (myosin) protein filaments. According to the sliding filament theory, muscles contract when these filaments slide past each other, powered by energy from ATP.

🎯 Exam Tip: When describing the sliding filament theory, remember to mention the role of ATP and the formation of cross-bridges between actin and myosin to secure full marks.

Cyclic Events in Muscle Contraction:

• Step 1: Myosin head binds to the actin filament, releasing inorganic phosphate (P_i).
• Step 2: ADP is released, triggering the power stroke that pulls the actin filament.
• Step 3: ATP binds to the myosin head, causing it to detach from the actin filament.
• Step 4: ATP undergoes hydrolysis to ADP and P_i, resetting the myosin head for the next cycle.

 

Question (B). Ragini, a 50 year old office goer, suffered hair-line cracks in her right and left foot in short intervals of time. She was worried about minor jerks leading to hair line cracks in bones. Doctor explained to her why it must be happening and prescribed medicines.

What must be the cause of Ragini’s problem? Why has it occurred? What precautions she should have taken earlier? What care she should take in future?
Answer:
1. Considering Ragini’s age, she may be undergoing menopause. After menopause, oestrogen level declines resulting in lower bone density.
2. Osteoporosis:
• In this disorder, bones become porous and hence brittle. It is primarily age related disease and is more common in women than men.
• Osteoporosis may be caused due to decreasing estrogen secretion after menopause, deficiency of vitamin D, low calcium diet, decreased secretion of sex hormones and thyrocalcitonin.
3. As age advances, bone resorption outpaces bone formation. Hence, the bones lose mass and become brittle. More calcium is lost in urine, sweat, etc., than it is gained through diet. Thus, prevention of disease is better than cure, and maintaining a balanced diet rich in calcium and vitamin D throughout life is essential to preserve skeletal strength.
In simple words: Ragini is likely suffering from osteoporosis, a condition where bones become weak and fragile due to a drop in estrogen levels after menopause. To prevent this, women should consume enough calcium and vitamin D, and take prescribed medications to strengthen their bones.

🎯 Exam Tip: When explaining bone disorders in older women, always link the cause to menopause and the decline of estrogen levels, as this is a key grading point.

 

Question (C). How does structure of actin and myosin help muscle contraction?
Answer:
i. Myosin filament:
1. Each myosin filament is a polymerized protein. Many meromyosins (monomeric proteins) constitute one thick filament.
2. Myosin molecule consists of two heavy chains (heavy meromyosin / HMM) coiled around each other forming a double helix. One end of each of these chains is projected outwardly is known as cross bridge. This end folds to form a globular protein mass called myosin head.
3. Two light chains are associated with each head forming 4 light chains/light meromyosin / LMM.
4. Myosin head has a special ATPase activity. It can split ATP to produce energy.
5. Myosin contributes 55% of muscle proteins.
6. In sarcomere, myosin tails are arranged to point towards the centre of the sarcomere and the heads point to the sides of the myofilament band. These structural features allow myosin to bind with actin during contraction.

Structure of Myosin Filament (Diagram Labels):

• Tail
• Heads
• Myosin filament
• Myosin head

In simple words: Myosin is a thick muscle protein made of many smaller units. It has tiny heads that use energy to grab and pull, which helps our muscles contract and move.

🎯 Exam Tip: Clearly label the parts of the myosin filament, especially the heavy meromyosin (HMM) head and light meromyosin (LMM) tail, to secure full marks in structural questions.

Question. Describe the structure and components of an actin filament.
Answer: Actin filament is a complex type of contractile protein. It is made up of three components:
1. F actin: It forms the backbone of actin filament. F actin is made up of two helical strands. Each strand is composed of polymerized G actin molecules. One ADP molecule is attached to G actin molecule.
2. Tropomyosin: The actin filament contains two additional protein strands that are polymers of tropomyosin molecules. Each strand is loosely attached to an F actin. In the resting stage, tropomyosin physically covers the active myosin-binding site of the actin strand.
3. Troponin: It is a complex of three globular proteins, is attached approx. 2/3^rd distance along each tropomyosin molecule. It has affinity for actin, tropomyosin and calcium ions. The troponin complex is believed to attach the tropomyosin to the actin. The strong affinity of troponin for calcium ions is believed to initiate the contraction process.

Actin Filament Diagram Labels:
• Tropomyosin
• Actin
• Troponin
• Actin filament
In simple words: Actin is a thin muscle protein made of three parts: F-actin (the main strand), tropomyosin (which covers the binding sites), and troponin (which acts like a switch when calcium is present).

🎯 Exam Tip: Clearly list and describe all three components—F-actin, tropomyosin, and troponin—to secure maximum marks in questions about contractile proteins.

 

Question (D). Justify the structure of atlas and axis vertebrae with respect to their position and function.
Answer:
i. Atlas vertebrae:
1. Atlas is the ring-like, 1^st cervical vertebrae. It has anterior, posterior arches and large lateral masses.
2. It lacks centrum and spinous process. The superior surfaces of the lateral masses are concave and are known as superior articular facets.
3. These facets articulate with the occipital condyles of the occipital bone thereby forming atlanto-occipital joints. This articulation permits ‘YES movement’ or nodding movement.
4. The inferior surfaces of the lateral masses known as inferior articular facets articulate with axis vertebrae, which helps facilitate the joint's overall stability and movement.
In simple words: The atlas is the very first neck bone that supports the skull. Because it lacks a central body and has a ring-like shape, it allows you to nod your head up and down to say "yes".

🎯 Exam Tip: Always highlight that the atlas vertebra lacks a centrum and spinous process, as this unique structural adaptation is a favorite topic for examiners.

ii. Axis Vertebrae:
1. It is the 2^nd cervical vertebrae.
2. A peg-like process called odontoid process projects superiorly through the anterior portion of the vertebral foramen of the atlas.
3. The odontoid process forms a pivot on which the atlas and head rotate. This arrangement allows ‘NO movement’ or side to side movement of the head.
4. The articulation formed between the anterior arch of atlas, the odontoid process of the axis and between their articular facets is called as atlanto-axial joint.

 

Question (E). Observe the blood report given below and diagnose the possible disorder.

Report D PERFECT PATHOLOGY
Test	Result	Normal value
Uric Acid	9.2	2.5 - 7.0 mg/l
Blood Urea Nitrogen (Bun)	24	10 - 20 mg/dl

Answer: On observing Report D, it is clear that the level of uric acid is more than normal, thus the patient must be suffering from gouty arthritis. Also, the elevated blood urea nitrogen (BUN) indicates dysfunctional liver and/or kidneys. It generally occurs due to decrease in GFR, caused by renal disease or obstruction of urinary tract. This diagnostic analysis helps in identifying metabolic and renal complications early.
In simple words: The blood report shows high levels of uric acid and urea nitrogen, which means the patient likely has gout (a painful joint condition) and their kidneys might not be filtering waste properly.

🎯 Exam Tip: Compare the patient's test values directly with the provided normal range values to accurately identify which parameters are elevated or depleted.

 

Question 4. Write Short Notes on Following Points

 

Question (A). Actin filament
Answer: Actin filament is a thin contractile protein filament found in muscle cells. It is composed of two helical strands of 'F' (filamentous) actin, along with regulatory proteins called tropomyosin and troponin. These filaments interact with myosin to facilitate muscle contraction through the sliding filament mechanism. This structural arrangement is essential for all voluntary and involuntary movements in the body.
In simple words: Actin filaments are thin protein threads in our muscles that slide past thicker threads to help our muscles contract and move.

🎯 Exam Tip: Remember that actin is the primary component of thin filaments, and always mention its association with regulatory proteins like troponin and tropomyosin.

Question (A). Actin filament
Answer:
It is a complex type of contractile protein. It is made up of three components:
1. F actin: It forms the backbone of actin filament. F actin is made up of two helical strands. Each strand is composed of polymerized G actin molecules. One ADP molecule is attached to G actin molecule.
2. Tropomyosin: The actin filament contains two additional protein strands that are polymers of tropomyosin molecules. Each strand is loosely attached to an F actin. In the resting stage, tropomyosin physically covers the active myosin-binding site of the actin strand.
3. Troponin: It is a complex of three globular proteins, is attached approx. 2/3rd distance along each tropomyosin molecule. It has affinity for actin, tropomyosin and calcium ions. The troponin complex is believed to attach the tropomyosin to the actin. The strong affinity of troponin for calcium ions is believed to initiate the contraction process.

Actin Filament Diagram Components:
• Tropomyosin
• Actin
• Troponin
• Actin filament
In simple words: Actin is a thin muscle protein made of three parts: F-actin (the main strand), tropomyosin (which blocks muscle contraction when resting), and troponin (which binds to calcium to start muscle contraction).

🎯 Exam Tip: Clearly distinguish between the roles of tropomyosin (blocking) and troponin (calcium-binding) to score full marks in descriptive questions.

 

Question (B). Myosin filament
Answer:
i. Myosin filament:
1. Each myosin filament is a polymerized protein. Many meromyosins (monomeric proteins) constitute one thick filament. This structural arrangement is essential for muscle contraction.
2. Myosin molecule consists of two heavy chains (heavy meromyosin / HMM) coiled around each other forming a double helix. One end of each of these chains is projected outwardly is known as cross bridge. This end folds to form a globular protein mass called myosin head.
3. Two light chains are associated with each head forming 4 light chains/light meromyosin / LMM.
4. Myosin head has a special ATPase activity. It can split ATP to produce energy.
5. Myosin contributes 55% of muscle proteins.
In simple words: Myosin is a thick protein filament in muscles made of many smaller units. It has a double-helix shape with "heads" that use energy (ATP) to help muscles contract.

🎯 Exam Tip: Remember to mention the ATPase activity of the myosin head and its role in energy production, as this is a key point examiners look for.

Question 6. Explain the arrangement of myosin tails and heads in a sarcomere.
Answer: In a sarcomere, myosin tails are arranged to point towards the centre of the sarcomere and the heads point to the sides of the myofilament band. This specific structural orientation is essential for the sliding filament mechanism of muscle contraction.
The diagram of the myosin filament contains the following labels:

• Tail
• Heads
• Myosin filament
• Myosin head

In simple words: In a muscle unit, the tails of myosin point to the middle, while their heads point outward to help pull and contract the muscle.

🎯 Exam Tip: Remember that myosin heads point outwards to easily bind with actin, which is crucial for the sliding filament mechanism.

 

Question (C). Role of calcium ions in contraction and relaxation of muscles.
Answer: Calcium ions play a major role in contraction and relaxation of muscles.
1. Calcium ions are released from the sarcoplasm during muscle contraction and stored in sarcoplasmic reticulum during muscle relaxation.
2. When a skeletal muscle is excited and an action potential travels along the T tubule, the concentration of calcium ions increases.
3. These calcium ions bind to troponin which in turn undergoes a conformational change that causes tropomyosin to move away from the myosin-binding sites on actin. Once these binding sites are free, myosin heads bind to them to form cross-bridges and the muscle fiber contracts.
4. The decrease in calcium ion concentration in the sarcoplasmic reticulum causes tropomyosin to slide back and block the myosin binding sites on actin. This causes the muscle to relax. This precise regulation ensures that muscles only contract when stimulated by a nerve impulse.
In simple words: Calcium acts like a key that unlocks muscle contraction. When calcium is released, it clears the path for muscle fibers to bind and pull; when calcium is pumped away, the muscle relaxes.

🎯 Exam Tip: Clearly list the step-by-step action of calcium binding to troponin and moving tropomyosin, as these specific protein names carry maximum marks.

 

Question 5. Draw Labelled Diagrams

 

Question (A). Synovial joint.
Answer: A synovial joint diagram typically includes key components such as articulating bones, articular cartilage, synovial cavity containing synovial fluid, and the joint capsule. This specialized structure allows for smooth, frictionless movement between bones.
In simple words: A synovial joint is a flexible joint filled with a lubricating fluid that helps our bones move smoothly without rubbing against each other.

🎯 Exam Tip: When drawing a synovial joint, always clearly label the synovial cavity, articular cartilage, and the outer joint capsule to secure full marks.

 

Question 1. Explain the structure and characteristics of synovial joints (freely movable joints / diarthroses).
Answer:
(i) Synovial joints / freely movable joints / diarthroses:
1. It is characterized by presence of a space called synovial cavity between articulating bones that renders free movement at the joint.
2. The articulating surfaces of bones at a synovial joint are covered by a layer of hyaline cartilage. It reduces friction during movement and helps to absorb shock. This cartilage acts as a smooth protective cushion for the bones.
3. Synovial cavity is lined by synovial membrane that forms synovial capsule. Synovial membrane secretes synovial fluid.
The components of a synovial joint include:

• Ligament
• Bone
• Synovial cavity (contains synovial fluid)
• Articular (hyaline) cartilage
• Articular capsule (comprising Fibrous layer and Synovial membrane)

4. Synovial fluid is a clear, viscous, straw coloured fluid similar to lymph. It is viscous due to hyaluronic acid. The synovial fluid also contains nutrients, mucous and phagocytic cells to remove microbes.
Synovial fluid lubricates the joint, absorbs shocks, nourishes the hyaline cartilage and removes waste materials from hyaline cartilage cells (as cartilage is avascular). Phagocytic cells destroy microbes and cellular debris formed by wear and tear of the joint.
5. If the joint is immobile for a while, the synovial fluid becomes viscous and as joint movement starts, it becomes less viscous.
6. The joint is provided with capsular ligament and numerous accessory ligaments. The fibrous capsule is attached to periosteum of articulating bones. The ligament helps in avoiding dislocation of joint.
7. The types of synovial joints are as follows:
1. Pivot joint: In this type of joint, the rounded or pointed surface of one bone articulates with a ring formed partly by another bone and partly by the ligament. Rotation only around its own longitudinal axis is possible. e.g. in joint between
In simple words: Synovial joints are highly movable joints where two bones meet inside a fluid-filled cavity. The synovial fluid acts like lubricating oil, reducing friction and absorbing shocks so our joints can move smoothly without pain.

🎯 Exam Tip: When describing synovial joints, remember to mention the role of synovial fluid in lubrication and shock absorption, as these are key terms examiners look for.

1. Pivot Joint

In a pivot joint, the primary movement is rotation. For example, between the atlas and axis vertebrae, the head turns side ways to form the ‘NO’ joint.

Diagram Labels (Pivot Joint):

• Odontoid process
• Transverse ligament
• Atlas
• Axis
• Pivot joint

🎯 Exam Tip: Remember that the pivot joint between the atlas and axis vertebrae is what allows you to shake your head "no". Always mention this specific example in your answers.

 

2. Ball and Socket Joint

The ball like surface of one bone fits into cup like depression of another bone forming a movable joint. Multi-axial movements are possible. This type of joint allows movements along all three axes and in all directions. e.g. Shoulder and hip joint.

Diagram Labels (Ball and Socket Joint):

• Pelvis
• Cartilage
• Head of femur
• Neck of femur
• Ball and socket joint

🎯 Exam Tip: The key characteristic of a ball and socket joint is "multi-axial movement" (movement in all directions). Be sure to highlight the shoulder and hip joints as classic examples.

 

3. Hinge Joint

In a hinge joint, convex surface of one bone fits into concave surface of another bone. In most hinge joints one bone remains stationary and other moves. The angular opening and closing motion (like hinge) is possible. In this joint only mono-axial movement takes place like flexion and extension. e.g. Elbow and knee joint.

Diagram Labels (Hinge Joint):

• Humerus
• Tricep
• Bicep
• Joint capsule (with synovial fluid)
• Radius
• Ulna
• Cartilage
• Hinge joint

🎯 Exam Tip: Clearly define "mono-axial movement" when describing a hinge joint, and use the analogy of a door hinge to explain its limited, back-and-forth motion.

Question. Explain the structure and examples of Condyloid, Gliding, and Saddle joints.
Answer:
4. Condyloid joint: It is an ellipsoid joint. The convex oval shaped projection of one bone fits into oval shaped depression in another bone. It is a biaxial joint because it permits movement along two axes viz, flexion, extension, abduction, adduction and circumduction is possible. e.g. Metacarpophalangeal joint.

Condyloid Joint Diagram Labels:
• Radius
• Ulna
• Articular cartilage
• Synovial membrane
• Ligament
• Synovial cavity
• Carpals

5. Gliding joint: It is a planar joint, where the articulating surfaces of bones are flat or slightly curved. These joints are non-axial because the motion they allow does not occur along an axis or a plane. e.g. Intercarpal and intertarsal joints.

6. Saddle joint: This joint is a characteristic of Homo sapiens. Here the articular surface of one bone is saddle-shaped and that of other bone fits into saddle (each bone forming this joint have both concave and convex areas). It is a modified condyloid joint in which movement is somewhat more free. It is a biaxial joint that allows flexion, extension, abduction, adduction and circumduction. e.g. Carpometacarpellar joint between carpal (trapezium) and metacarpal of thumb.

Saddle Joint Diagram Labels:
• Carpal (Trapezium)
• 1st Metacarpal

These specialized synovial joints provide the human body with incredible flexibility and range of motion for daily activities.
In simple words: Condyloid, gliding, and saddle joints are different types of highly movable joints that allow our bones to slide, bend, and rotate in various directions.

🎯 Exam Tip: Always memorize specific examples for each joint type, such as the thumb's carpometacarpal joint for the saddle joint, as these are frequently asked in exams.

 

Question (B). Different cartilagenous joints.
Answer: Cartilaginous / slightly movable joints / amphiarthroses:
In these joints, the bones are joined together by cartilage (either hyaline cartilage or fibrocartilage). They allow only limited movement. These joints are classified into two main types:
1. Synchondroses (Primary cartilaginous joints): The bones are held together by a temporary or permanent layer of hyaline cartilage, which eventually ossifies in some cases, such as the epiphyseal plate between the diaphysis and epiphysis of a growing long bone.
2. Symphyses (Secondary cartilaginous joints): The connecting medium is a broad, flat disc of fibrocartilage, which remains unossified throughout life, such as the pubic symphysis and intervertebral discs. These joints act as excellent shock absorbers to protect the skeletal structure from sudden impacts.
In simple words: Cartilaginous joints are slightly movable joints where bones are connected by tough cartilage, allowing only a small amount of movement for stability and shock absorption.

🎯 Exam Tip: Clearly distinguish between primary (synchondroses) and secondary (symphyses) cartilaginous joints by highlighting the type of cartilage involved and providing clear examples like intervertebral discs.

 

Question. Explain the features and classification of joints that are neither fixed nor freely movable (Cartilaginous joints).
Answer: These joints are neither fixed nor freely movable. Articulating bones are held together by hyaline or fibrocartilages. They are further classified as

a. Synchondroses: The two bones are held together by hyaline cartilage. They are meant for growth. On completion of growth, the joint gets ossified, e.g. Epiphyseal plate found between epiphysis and diaphysis of a long bone, Rib – Sternum junction.
(Diagram labels: Epiphyseal plates, Epiphysis, Diaphysis, Synchondroses)

b. Symphysis: In this type of joint, broad flat disc of fibrocartilage connects two bones. It occurs in mid-line of the body. e.g. Intervertebral discs, manubrium and sternum, pubic symphysis.
In simple words: These are slightly movable joints where bones are joined by cartilage. Synchondroses are temporary joints that turn into bone after growth is complete, while symphysis joints use flat cartilage discs to connect bones along the center line of the body.

🎯 Exam Tip: Clearly distinguish between synchondroses and symphysis by highlighting their cartilage types (hyaline vs. fibrocartilage) and providing classic examples like the epiphyseal plate and intervertebral discs to secure full marks.

Synovial Joint Structure

• Ligament
• Bone
• Synovial cavity (contains synovial fluid)
• Articular (hyaline) cartilage
• Articular capsule (comprising Fibrous layer and Synovial membrane)

 

Symphysis Structure

• Intervertebral foramen
• Vertebral body
• Anulus fibrosus of intervertebral disc

 

Pelvic Girdle Structure

• Sacrum
• Acetabulum
• Superior ramus of pubis
• Obturator foramen
• Inferior ramus of pubis

 

Practical / Project

 

Question. Identify the following diagrams and demonstrate the concepts in classroom.
Answer: The diagrams A, B and C represent Class I, Class II and Class III lever respectively. Understanding how these levers function in the human body helps us analyze movement efficiency.

1. Class I lever: The joint between the first vertebra and occipital condyle of skull is an example of Class I lever. The force is directed towards the joints (fulcrum); contraction of back muscle provides force while the part of head that is raised acts as resistance.
* Arrangement: Resistance (R) — Fulcrum (F) — Effort (E)

2. Class II lever: Human body raised on toes is an example of Class II lever. Toe acts as fulcrum, contracting calf muscles provide the force while raised body acts as resistance.
* Arrangement: Effort (E) — Resistance (R) — Fulcrum (F)

3. Class III lever: Flexion of forearm at elbow exhibit lever of class III. Elbow joint acts as fulcrum and radius, ulna provides resistance. Contracting bicep muscles provides force for the movement.
* Arrangement: Resistance (R) — Effort (E) — Fulcrum (F)

[Students are expected to perform the given activity on their own]
In simple words: Our bones and joints work like mechanical levers where joints act as pivot points (fulcrums), muscles provide the pull (effort), and body parts act as the weight being moved (resistance).

🎯 Exam Tip: Remember the acronym FRE (Fulcrum, Resistance, Effort in the middle) to easily identify Class I, II, and III levers in human anatomy questions.

 

Question 1. Streaming of protoplasm, peristalsis, walking, running, etc. Which of the above-mentioned movements are internal? Which are external? Can you add few more examples?
Answer:
1. Streaming of protoplasm, peristalsis are internal movements. Walking and running are external movements.
2. Examples of internal movement: Contraction and relaxation heart, inspiration and expiration, contraction of blood vessels, etc.
3. Examples of external movement: Swimming; movement tongue, jaws, snout, tentacles, movement of ear pinna, etc.
In simple words: Internal movements happen inside our body without us seeing them, like our heart beating. External movements are actions we can see from the outside, like walking or swimming.

🎯 Exam Tip: Clearly categorize your examples into internal and external movements using numbered lists to make it easy for the examiner to grade.

Can You Recall? (Textbook Page No. 193)

 

Question 1. Which are different types of muscular tissues?
Answer:
1. Smooth / non-striated / visceral / involuntary muscles
2. Cardiac muscles
3. Skeletal / straited / voluntary muscles.
In simple words: Our body has three main types of muscles: skeletal muscles that help us move, smooth muscles inside our organs, and cardiac muscles in our heart.

🎯 Exam Tip: Remember to write all alternative names (like visceral for smooth, or striated for skeletal) to show a complete understanding of muscular tissues.

 

Question 2. Name the type of muscles which bring about running and speaking.
Answer: Skeletal muscles (Voluntary muscles) are responsible for these movements.
In simple words: Skeletal muscles are voluntary muscles, meaning we can control them whenever we want to run or talk.

🎯 Exam Tip: Always mention both terms—skeletal and voluntary—to secure full marks for questions on physical activities.

 

Question 3. Name the muscles which do not contract as per our will.
Answer: Involuntary muscles (smooth muscles and cardiac muscles) do not contract according to our conscious will.
In simple words: Involuntary muscles work automatically on their own, like the muscles that pump our heart or digest our food.

🎯 Exam Tip: Clearly state both smooth and cardiac muscles as examples of involuntary muscles to demonstrate a complete answer.

 

Question 4. Which type of muscles show rhythmic contractions?
Answer: Cardiac muscles show rhythmic contractions throughout a person's lifetime without getting tired.
In simple words: Cardiac muscles in the heart contract and relax in a steady, rhythmic beat to pump blood.

🎯 Exam Tip: Mention that cardiac muscles never fatigue, as this is a unique and key characteristic of rhythmic contractions.

 

Question 5. Which type of muscle is present in the diaphragm of the respiratory system?
Answer: Skeletal muscle is present in the diaphragm of the respiratory system. This muscle plays a vital role in controlling our breathing patterns.
In simple words: The diaphragm is made of skeletal muscle, which helps us breathe in and out.

🎯 Exam Tip: Remember that even though breathing is usually automatic, the diaphragm is made of skeletal muscle which can also be controlled voluntarily when you hold your breath.

 

Question 6. State the functions of:
1. Smooth muscles
2. Cardiac muscles
3. Striated muscles
Answer:
1. Smooth muscles: They bring about involuntary movements like peristalsis in the alimentary canal, constriction and dilation of blood vessels.
2. Cardiac muscles: They bring about contraction and relaxation of the heart.
3. Striated muscles: They control voluntary movements of limbs, head, trunk, eyes, etc. These different muscle types work in harmony to keep our body functioning properly.
In simple words: Smooth muscles handle automatic jobs like digestion, cardiac muscles keep our heart beating, and striated muscles let us move our arms and legs whenever we want.

🎯 Exam Tip: Clearly classify these muscles into voluntary (striated) and involuntary (smooth and cardiac) to secure full marks in classification questions.

 

Can You Recall? (Textbook Page No. 193)

 

Question 1. Name the part of human skeleton situated along the vertical axis.
Answer: Axial skeleton is situated along the vertical axis of the human body. It forms the central core that supports our posture and protects vital organs.
In simple words: The axial skeleton is the central part of our skeleton that runs straight down the middle of our body.

🎯 Exam Tip: Always mention that the axial skeleton includes the skull, vertebral column, and rib cage to show a complete understanding.

 

Question 2. Give an account of bones of human skull.
Answer: Skull is made up of 22 bones. It is located at the superior end of vertebral column. The bones of skull are joined by fixed or immovable joints except for jaw. Skull consists of cranium or brain box and facial bones. These bones provide a strong protective shield for our brain and support our facial features.
In simple words: The skull has 22 bones that protect our brain and shape our face. All of these bones are locked tightly in place, except for the lower jaw which moves so we can eat and talk.

🎯 Exam Tip: Do not forget to highlight that the lower jaw is the only movable bone in the skull, as this is a highly tested point in exams.

i. Cranium

It is made up of four median bones and two paired bones.

1. Frontal bone: It is median bone (unpaired) forming forehead, roof of orbit (eye socket) and the most anterior part of cranium. It is connected to two parietals, sphenoid and ethmoid bone.

2. Parietal bones: These paired bones form the roof of cranium and greater portion of sides of the cranium.

3. Temporal bones: These paired bones are situated laterally just above the ear on either side. Each temporal bone gives out zygomatic process that joins zygomatic bone to form zygomatic arch. Just at the base of zygomatic process is mandibular fossa, a depression for mandibles (lower jaw bone) that forms the only movable joint of the skull. This bone harbors the ear canal that directs sound waves into the ear. The processes of temporal bones provide points for attachment for various muscles of neck and tongue.

4. Occipital bone: It is a single bone present at the back of the head. It forms the posterior part and most of the base of cranium. The inferior part of this bone shows foramen magnum, the opening through which medulla oblongata connects with spinal cord. On the either sides of foramen magnum are two prominent protuberances called occipital condyles. These fit into the corresponding depressions present in 1^st vertebra.

5. Sphenoid bone: Median bone present at the base of the skull that articulates with all other cranial bones and holds them together. This butterfly shaped bone has a saddle shaped region called sella turcica. In this hypophyseal fossa, the pituitary gland is lodged.

6. Ethmoid bone: This median bone is spongy in appearance. It is located anterior to sphenoid and posterior to nasal bones. It contributes to formation of nasal septum and is major supporting structure of nasal cavity.

 

ii. Facial Bones

Fourteen facial bones give a characteristic shape to the face. The growth of face stops of the age of 16.

Following bones comprise the facial bones:

1. Nasals: These are paired bones that form the bridge of nose.

2. Maxillae: These form the upper jaw bones. They are paired bones that join with all facial bones except mandible. Upper row of teeth are lodged maxillae.

3. Palatines: These are paired bones forming the roof of buccal cavity or floor of the nasal cavity.

Lateral View of Skull (Diagram Labels):

• Frontal bone
• Sphenoid bone
• Nasal bone
• Ethmoid bone
• Lacrimal bone
• Zygomatic bone
• Maxilla
• Mandible
• Parietal bone
• Temporal bone
• Occipital bone
• Mastoid process

4. Zygomatic bones: They are commonly called as cheek bones.

5. Lacrimal bones: These are the smallest amongst the facial bones. These bones form the medial wall of each orbit. They have lacrimal fossa that houses lacrimal sacs. These sacs gather tears and send them to nasal cavity.

6. Inferior nasal conchae: They form the part of lateral wall of nasal cavity. They help to swirl and filter air before it passes to lungs.

7. Vomer: The median, roughly triangular bone that forms the inferior portion of nasal septum.

8. Mandible: This median bone forms the lower jaw. It is the largest and strongest facial bone. It is the only movable bone of skull. It has curved horizontal body and two perpendicular branches i.e. rami. These help in attachment of muscles. It has lower row of teeth lodged in it.

Think About It (Textbook Page No. 193)

 

Question 1. Did you ever feel tickling in muscles?
Answer: Yes, the tickling sensation in muscles can be felt and sometimes it is also accompanied by itching sensation. This mild irritation often triggers a natural urge to scratch or move the muscle.
In simple words: Yes, you can sometimes feel a tickling or itching feeling in your muscles. This is a normal sensation that makes you want to move or scratch.

🎯 Exam Tip: When answering experiential questions, state your observation clearly and briefly explain the physiological sensation associated with it.

Question 2. What is locomotion?
Answer: The change in locus of whole body of living organism from one place to another place is called locomotion. This active movement is essential for survival, finding food, and escaping danger.
In simple words: Locomotion is when a living thing moves its entire body from one place to another. It is how animals travel around.

🎯 Exam Tip: Remember to define locomotion as the movement of the entire organism from one location to another, rather than just the movement of individual body parts.

 

Question 3. State the four basic types of locomotory movements seen in animals.
Answer: The four basic types locomotory movements seen in animals are:
1. Amoeboid movement: It is performed by pseudopodia, e.g. leucocytes.
2. Ciliary movement: It is performed by cilia, e.g. ciliated epithelium. In Paramoecium, cilia help in passage of food through cytopharynx.
3. Whirling movement: It is performed by flagella, e.g. sperms.
4. Muscular movement: It is performed by muscles, with the help of bones and joints. These diverse mechanisms allow different organisms to adapt to their specific environments.
In simple words: Animals move in four main ways: using temporary body extensions, tiny hair-like structures, whip-like tails, or muscles and bones.

🎯 Exam Tip: Clearly list all four types with their respective structures (pseudopodia, cilia, flagella, muscles) and examples to score full marks.

 

Question 4

 

Question 1. Why do muscles show spasm after rigorous contraction?
Answer:
1. Rigorous contraction of muscles occurs during strenuous activities (swimming, running, cycling, aerobics, etc.)
2. Muscle contraction requires energy. Glucose in muscle cells breakdown during anerobic respiration resulting in accumulation of lactic acid.
3. This lactic acid buildup triggers muscle spasm around muscle cells. This temporary condition can be relieved by resting and stretching the affected muscle.
In simple words: When we exercise very hard, our muscles run out of oxygen and produce lactic acid. This buildup of acid causes the muscles to cramp up.

🎯 Exam Tip: Be sure to mention "anaerobic respiration" and "lactic acid accumulation" as these are the key scientific terms examiners look for.

 

Question 2. Why do we shiver during winter?
Answer:
1. Humans are homeotherms as they can regulate their body temperature with respect to the surrounding temperature. During winter, when temperature drops, involuntary muscle contractions occur to generate heat and maintain body temperature.
In simple words: Humans need to keep their body temperature steady. When it is cold, our muscles shake rapidly to produce heat and keep us warm.

🎯 Exam Tip: Use the term "homeotherms" and explain that shivering is a mechanism of heat generation through rapid, involuntary muscle contractions.

Can You Tell? (Textbook Page No. 194)

 

Question 1. Why are movement and locomotion necessary among animals?
Answer: Movement is one of the important characteristics of all the living organisms. Animals exhibit wide range of movements like rhythmic beating of heart, movement of diaphragm during respiration, ingestion of food, movement of eyeballs, etc. Locomotion results into change in place or location of an organism. Animals locomote in search of food, mate, shelter, breeding ground, while escaping from the enemy, etc. Thus, locomotion and movement are necessary to support the living of animals. These processes are fundamental for survival and adaptation in a dynamic environment.
In simple words: Animals need to move their body parts to perform daily functions like breathing and eating, and they need to travel from one place to another to find food and stay safe.

🎯 Exam Tip: Clearly distinguish between movement (local body actions) and locomotion (displacement of the whole body) to score full marks.

 

Question 2. All locomotions are movements but all movements are not locomotion. Justify
Answer: Locomotion occurs when body changes its position, however all movements may not result in locomotion. Thus, all locomotions are movements but all movements are not locomotion. For instance, waving a hand is a movement, but it does not change the organism's overall location.
In simple words: Every time you travel to a new place, you are moving your body. But you can also move your body, like blinking or waving, without actually traveling anywhere.

🎯 Exam Tip: Use a simple everyday example, like nodding your head versus walking, to make your justification clear and convincing.

 

Question 3. Kriti was diagnosed with knee tendon injury. She asked the doctor whether she will be able to walk due to the injury? If not then state the reason.
Answer: Knee tendon injury affects the ability to walk. Kriti may not be able to walk freely as the tendons attached to the bones help in the movement of the parts of skeleton. Without healthy tendons, the force generated by muscles cannot be efficiently transmitted to the bones to facilitate walking.
In simple words: Tendons act like strong ropes connecting muscles to bones. If the knee tendon is injured, the leg muscles cannot pull the bones properly to make her walk.

🎯 Exam Tip: Remember to define the role of tendons as connectors between muscles and bones when explaining movement injuries.

 

Question 4. What are antagonistic muscles? Explain with example.
Answer: Antagonistic muscles are pairs of muscles that act opposite to each other. When one muscle contracts, the other relaxes to produce movement. For example, the biceps and triceps in the upper arm work antagonistically; flexing the elbow requires the biceps to contract and the triceps to relax, while extending the elbow requires the triceps to contract and the biceps to relax. This coordinated action ensures smooth and controlled movement of the skeletal system.
In simple words: Antagonistic muscles work in pairs where one pulls while the other relaxes. A great example is your arm: when you bend your elbow, your biceps tighten and your triceps relax.

🎯 Exam Tip: Always use the biceps and triceps pair as your go-to example when explaining antagonistic muscle action.

 

Question 5. Describe the antagonistic muscles in detail.
Answer: Following are the important antagonistic muscles:
1. Flexor and extensor: Flexor muscle on contraction results into bending or flexion of joint, e.g. Biceps. Extensor muscle on contraction results in straightening or extension of a joint, e.g. Triceps. This coordinated action allows smooth movement of limbs.
2. Abductor and adductor: Abductor muscle moves a body part away from the body axis. e.g. Deltoid muscle of shoulder moves the arm away from the body. Adductor muscle moves a body part towards the body axis, e.g. Latissimus dorsi of shoulder moves the arm near the body.
3. Pronator and supinator: Pronator turns the palm downwards and supinator turns the palm upward.
4. Levator and depressor: Levator raises a body part and the depressors lower the body part.
5. Protractor and retractor: Protractor moves forward, whereas the retractor moves backward.
6. Sphincters: Circular muscles present in the inner walls of anus, stomach, etc., for closure and opening.
In simple words: Antagonistic muscles work in pairs where one muscle contracts to move a body part, and the other contracts to move it back. Examples include muscles that bend and straighten joints, or move limbs closer to and further from the body.

🎯 Exam Tip: Memorize at least three pairs of antagonistic muscles with their specific functions and examples, like flexor-extensor (biceps-triceps), to score full marks.

 

Question 6. Differentiate between:
(i) Flexor and extensor muscles
Answer:

Flexor Muscles	Extensor Muscles
These muscles contract to bend a joint (flexion).	These muscles contract to straighten or extend a joint (extension).
They bring the connected bones closer to each other.	They move the connected bones further apart from each other.
Example: Biceps of the upper arm.	Example: Triceps of the upper arm.

These opposing muscle groups work in perfect harmony to control joint mobility.
In simple words: Flexor muscles bend our joints (like folding your arm), while extensor muscles straighten them out (like stretching your arm).

🎯 Exam Tip: When writing differences, always present them in a tabular format with clear, corresponding points and include relevant examples for both.

Flexor Muscles		Extensor Muscles
a.	Flexor muscles contract and bring about the bending or flexion of joint.	a.	Extensor muscles contract and bring about the straightening or extension of joint.
b.	These muscles decrease the angle between the bones on two sides of a joint.	b.	These muscles increase the angle between the components of limb.
e.g.	Biceps	e.g.	Triceps

ii. Pronator and supinator: Pronator turns the palm downwards and supinator turns the palm upward.

Can You Recall? (Textbook Page No. 194)

 

Question 1. Comment on contraction of skeletal muscles.
Answer: Skeletal muscles show quick and strong voluntary contractions. They bring about voluntary movements of the body. This intricate process ensures that our muscles only contract when receiving a direct signal from the nervous system. For mechanism of muscle contraction:

When the muscles are relaxed, the active sites remain covered with tropomyosin and troponin complex. Due to this, myosin cannot interact with active site of actin and thus contraction cannot occur.

1. When an impulse (action potential) comes to muscle through motor end plate, it spreads throughout the sarcolemma of the myofibril.
2. The transverse tubules of sarcoplasmic reticulum release large number of \( \text{Ca}^{++} \) ions into sarcoplasm. These calcium ions interact with the troponin molecules and the interaction inactivates troponin-tropomyosin complex. This causes change in the structure of tropomyosin.
3. As a result, tropomyosin gets detached from the active site of actin (F actin) filament, exposing the active site for actin.
In simple words: Skeletal muscles move our body through voluntary actions. When a nerve signal reaches the muscle, it releases calcium ions which clear the path for muscle proteins to bind and pull together, causing contraction.

🎯 Exam Tip: Clearly outline the sequence of events starting from the nerve impulse to calcium release and finally the exposure of the actin active site to secure maximum marks.

Do You Know How (Textbook Page No. 195)

 

Question 1. Do skeletal muscles contract and bring about movement and locomotion?
Answer: When the muscles are relaxed, the active sites remain covered with tropomyosin and troponin complex. Due to this, myosin cannot interact with active site of actin and thus contraction cannot occur. This coordinated sequence of molecular interactions ensures precise control over muscle movements.
1. When an impulse (action potential) comes to muscle through motor end plate, it spreads throughout the sarcolemma of the myofibril.
2. The transverse tubules of sarcoplasmic reticulum release large number of \( \text{Ca}^{++} \) ions into sarcoplasm. These calcium ions interact with the troponin molecules and the interaction inactivates troponin-tropomyosin complex. This causes change in the structure of tropomyosin.
3. As a result, tropomyosin gets detached from the active site of actin (F actin) filament, exposing the active site for actin.
4. The myosin head cleaves the ATP to derive energy and gets attached to the uncovered active site of actin. This results into the formation of acto-myosin complex.
5. The myosin heads are now tilted backwards and pull the attached actin filament inwardly. This results in contraction of the muscle fibres.
In simple words: When a nerve signal reaches a muscle, it triggers the release of calcium. This calcium uncovers the binding sites on actin, allowing myosin heads to attach and pull, which shortens and contracts the muscle.

🎯 Exam Tip: Remember to list the steps of muscle contraction in chronological order, highlighting the role of calcium ions and ATP hydrolysis to score full marks.

 

Internet My Friend (Textbook Page No. 196)

 

Question 1. Collect information about ‘T’ tubules of sarcoplasmic reticulum.
Answer: 1. T tubules or the transverse tubules are invaginations of the sarcolemma penetrating into the myocyte interior, forming a highly branched and interconnected network. These tubules play a critical role in ensuring that the action potential reaches the deep interior of the muscle fiber simultaneously.
In simple words: T-tubules are like deep tunnels in a muscle cell that help electrical signals travel quickly from the outside to the inside so the whole muscle contracts at once.

🎯 Exam Tip: Clearly define T-tubules as extensions of the sarcolemma and emphasize their role in transmitting electrical impulses deep into the muscle cell.

Can You Tell? (Textbook Page No. 197)

 

Question 1. Explain the chemical changes taking place in muscle contraction.
Answer: The muscle undergoes various chemical changes during contraction, they are as follows:
1. A nerve impulse arrives at the motor nerve. The neurotransmitter – acetylcholine is released at the neuromuscular junction (N-M junction or motor endplate) enters into the sarcomere.
2. This leads to inflow of \( \text{Na}^+ \) inside the sarcomere and generates an action potential in the muscle fibre.
3. The action potential passes down the T tubules and activates calcium channels in the T tubular membrane. Activation of calcium channel allows calcium ions to pass into the sarcoplasm. These \( \text{Ca}^{++} \) ions binds to the specific sites on troponin of actin filaments and a conformational change occurs in the troponin – tropomyosin complex, thereby removing the masking of active sites for myosin on the actin filament.
4. In the myosin head, the enzyme ATPase gets activated in the presence of \( \text{Ca}^{++} \) and converts ATP into ADP and inorganic phosphate.
5. This energy from ATP hydrolysis is utilized by myosin bridges or myosin heads to bind with active sites of actin and form actomyosin complex pulling the actin filaments towards the centre of sarcomere. The myosin heads are now tilted backwards and pull the attached actin filament inwardly towards them. The actin filament slides over mysosin and contraction occurs. This sliding filament mechanism is the fundamental basis of muscle shortening.
6. Also, the ADP needs to be converted back to ATP immediately as they required for muscular contraction, This is achieved in the muscles by the
In simple words: Muscle contraction starts when a nerve signal releases calcium inside the muscle cell. This calcium unlocks the muscle fibers, allowing them to link up and use energy from ATP to slide past each other and shorten the muscle.

🎯 Exam Tip: Clearly list the sequential steps of muscle contraction, highlighting the roles of calcium ions, ATP hydrolysis, and the formation of the actomyosin complex to secure full marks.

 

Question 2. Why are muscle rich in creatine phosphate?
Answer:
1. Creatine phosphate or phosphocreatine is formed from ATP, when the muscle is in relaxed state. It is a phosphorylated form of creatine.
2. Muscle cells contain creatine phosphate which acts as energy reserve as this high energy compound acts as a phosphate donor for ATP formation. This reserve ensures that muscles do not easily run out of energy during sudden bursts of activity.
3. ATP acts as an immediate source of energy for contraction
In simple words: Muscles store creatine phosphate as a backup battery. When muscles work hard and run out of quick energy (ATP), this backup helps recreate ATP very fast so the muscles can keep moving.

🎯 Exam Tip: Remember to highlight that creatine phosphate acts as a "phosphate donor" to quickly regenerate ATP during muscle activity.

 

Question 3. Explain the mechanism of muscle contraction and relaxation.
Answer:
Mechanism of muscle contraction:
When the muscles are relaxed, the active sites remain covered with tropomyosin and troponin complex. Due to this, myosin cannot interact with active site of actin and thus contraction cannot occur. This resting state is crucial for preventing unwanted muscle tension.
1. When an impulse (action potential) comes to muscle through motor end plate, it spreads throughout the sarcolemma of the myofibril.
2. The transverse tubules of sarcoplasmic reticulum release large number of \( \text{Ca}^{++} \) ions into sarcoplasm. These calcium ions interact with the troponin molecules and the interaction inactivates troponin-tropomyosin complex. This causes change in the structure of tropomyosin.
3. As a result, tropomyosin gets detached from the active site of actin (F actin) filament, exposing the active site for actin.
In simple words: When a nerve signal tells a muscle to move, calcium ions are released inside the muscle cells. These calcium ions unlock the blocked active sites on the muscle fibers, allowing the contraction process to begin.

🎯 Exam Tip: Clearly describe the role of calcium ions (\( \text{Ca}^{++} \)) in binding to troponin, as this is the key trigger that unmasks the active sites on actin.

4. The myosin head cleaves the ATP to derive energy and gets attached to the uncovered active site of actin. This results into the formation of actomyosin complex.

5. The myosin heads are now tilted backwards and pull the attached actin filament inwardly. This results in contraction of the muscle fibres.

Muscle Relaxation: During relaxation, all the events occur in reverse direction as that of muscle contraction.

1. When the stimulation is terminated, the actomyosin complex is broken down and myosin head gets detached from actin filaments. This process utilizes ATP.
2. Also, the \( \text{Ca}^{++} \) ions are pumped back into the sarcoplasmic reticulum. This process too is an energy dependent process and utilizes ATP.
3. As a result, the troponin-tropomyosin complex is restored again which covers the active sites of actin filament, due to disappearance of the \( \text{Ca}^{++} \) ions. The interaction between actin and myosin ceases and the actin filaments return back to their original position.
4. This results in muscle relaxation.

Diagram: Relaxation and Contraction of Muscle

• Sarcomere
• Thick filament (myosin filament)
• Thin filament (actin filament)
• Process: Relaxation and contraction of muscle

 

Question 4. What do you understand by muscle twitch?
Answer: Single muscle twitch: A single muscle twitch is a rapid, involuntary contraction followed by the relaxation of a muscle fiber in response to a single stimulus. This physiological response can be recorded on a kymograph to study the mechanical properties of muscle contraction. It typically consists of three distinct phases: the latent period, the contraction phase, and the relaxation phase.
In simple words: A muscle twitch is a quick, single contraction and relaxation of a muscle when it receives a single electrical signal from a nerve.

🎯 Exam Tip: To score full marks, remember to mention the three phases of a muscle twitch: the latent period, contraction phase, and relaxation phase.

Single Muscle Twitch

It is a muscle contraction initiated by a single brief-stimulation. It occurs in 3 stages: a latent period of no contraction, a contraction period and a relaxation period.

• The involuntary contraction of muscle fibers is known as muscle twitch.
• Muscle twitch is also known as fasciculation.
• It is caused due accumulation of lactic acid in muscles.

Do You Know How (Textbook Page No. 198)

 

Question 1. Exoskeletal components change from lower to higher group of animals. These include chitinous structures, nails, horns, hooves, scales, hair, shell, plates, fur, muscular foot, tube feet, etc.
Answer: This statement highlights the evolutionary diversity of exoskeletons, which adapt to meet the specific survival and locomotor needs of different animal groups. As animals evolved, their outer coverings became more specialized to support complex movements.
In simple words: Different animals have different outer coverings—like shells on snails or hooves on horses—that have evolved to help them survive and move in their environments.

🎯 Exam Tip: Be prepared to identify which group of animals possesses which type of exoskeleton (e.g., chitin in insects, shells in molluscs).

 

Question 1. Do you know any of these exoskeletal structures help in movement and locomotion?
Answer: Nails, hooves, scales, plates, muscular foot and tube feet help in movement and locomotion. These structures provide the necessary support and leverage for animals to move.
In simple words: Yes, parts like nails, hooves, scales, and tube feet help different animals grip the ground and move around.

🎯 Exam Tip: Remember to list specific examples like tube feet (for starfish) and muscular foot (for snails) to show a clear understanding of different animal groups.

 

Question 2. How do scales and plates help in movement and locomotion?
Answer: Scales and plates in reptiles like snakes provide grip to move on rough edgy surfaces. They act as contact points that prevent slipping during locomotion.
In simple words: Scales and plates act like the tread on shoes, helping reptiles grip the ground so they can slide forward without slipping.

🎯 Exam Tip: Mentioning reptiles, specifically snakes, as an example helps illustrate how scales function as friction-generating structures.

 

Question 3. Are scales of a fish and that of snake similar?
Answer: Fishes have dermal scales (bony scales), whereas reptiles like snakes have epidermal scales or scutes (horny, tough extensions of outer layer of skin i.e., stratum corneum). This structural difference reflects their adaptation to aquatic versus terrestrial environments.
In simple words: No, they are different. Fish scales grow from the inner layer of skin (dermal), while snake scales are tough outer skin layers (epidermal) that protect them from drying out.

🎯 Exam Tip: Clearly distinguish between 'dermal' (for fish) and 'epidermal' (for snakes) to secure full marks on this comparison.

 

Question 4. Find out more information about exoskeletal structures and their role in movement and locomotion.
Answer: Exoskeletal structures like the chitinous cuticle in insects provide attachment points for muscles, enabling precise movements. In molluscs, the shell protects the body while the muscular foot facilitates crawling. These diverse structures are essential for protection, support, and locomotion across various species.
In simple words: Outer skeletons, like insect shells or crab claws, give muscles a solid place to pull against, which allows these animals to walk, jump, or swim.

🎯 Exam Tip: Use examples like insects (chitinous exoskeleton) and crabs to explain how rigid outer coverings work with muscles to produce movement.

 

Question 2. Name the tissues that form the structural framework of the body.
Answer: Cartilage and bone. These specialized connective tissues work together to support the body's weight.
In simple words: Cartilage and bone are the two main tough tissues that make up our body's inner frame, giving us shape and support.

🎯 Exam Tip: Remember that bone is hard and rigid, while cartilage is flexible and acts as a cushion between joints.

 

Do You Remember? (Textbook Page No. 198)

 

Question 1. What are the components of skeletal system?
Answer: The components of skeletal system are bones, tendons, ligaments and joint. Together, they form a highly coordinated network that allows for smooth bodily movements.
In simple words: Our skeletal system is not just made of bones; it also includes the joints where bones meet, and the tough cords (tendons and ligaments) that tie everything together.

🎯 Exam Tip: Do not forget to list all four components—bones, joints, ligaments, and tendons—to secure full marks.

 

Question 2. What type of bones are present in our body?
Answer: Long bones, short bones, flat bones, irregular bones and sesamoid bones. Each of these categories is structurally adapted to perform specific mechanical functions.
In simple words: Our body has five different shapes of bones: long ones like in our arms, short ones in our wrists, flat ones like our ribs, odd-shaped irregular ones, and tiny seed-like sesamoid bones.

🎯 Exam Tip: Memorize the five types of bones by associating each with a specific example from the human body.

 

Question 3. How do bones help in various ways?
Answer:
1. Bones form the framework of our body and thus provide shape to the body.
2. They protect vital organs thus help in the smooth functioning of body.
3. The joints between the bones help in movement and locomotion.
4. They provide firm surface for attachment of muscles.
5. They are reservoirs of calcium and form important site for hemopoiesis. This production of blood cells is vital for sustaining life.
In simple words: Bones do many jobs: they give our body its shape, protect soft organs like the brain and heart, help us move, hold our muscles, and even make new blood cells.

🎯 Exam Tip: When listing the functions of bones, make sure to mention 'hemopoiesis' (blood cell production) as it is a key scientific term examiners look for.

Use Your Brain Power. (Textbook Page No. 198)

 

Question 1. Can you compare bone, muscle and joint which help in locomotion with any simple machines you have studied earlier?
Answer: Bone, muscle and joint can be compared to the simple machines called levers. Joints act as fulcrum, respective muscle generates the force required to move the bone associated with joint. This biological system works efficiently to allow a wide range of movements.
In simple words: Our bones, muscles, and joints work together just like levers (like a seesaw) to help us move, where the joint is the pivot point and the muscle provides the force.

🎯 Exam Tip: Remember to clearly identify the joint as the fulcrum, the muscle as the source of effort, and the bone as the lever arm to get full marks.

 

Question 2. Explain the three types of lever found in human body.
Answer: The three types of lever are as follows:
1. Class I lever: The joint between the first vertebra and occipital condyle of skull is an example of Class I lever. The force is directed towards the joints (fulcrum); contraction of back muscle provides force while the part of head that is raised acts as resistance. (Arrangement: Resistance — Fulcrum — Effort)
2. Class II lever: Human body raised on toes is an example of Class II lever. Toe acts as fulcrum, contracting calf muscles provide the force while raised body acts as resistance. (Arrangement: Effort — Resistance — Fulcrum)
3. Class III lever: Flexion of forearm at elbow exhibit lever of class III. Elbow joint acts as fulcrum and radius, ulna provides resistance. Contracting bicep muscles provides force for the movement. (Arrangement: Resistance — Effort — Fulcrum) Understanding these levers helps us appreciate how our musculoskeletal system optimizes force and movement.
In simple words: The human body uses three types of levers: Class I (like nodding your head, with the pivot in the middle), Class II (like standing on your toes, with the weight in the middle), and Class III (like bending your arm, with the muscle force in the middle).

🎯 Exam Tip: Draw simple line diagrams showing the relative positions of Fulcrum (F), Resistance (R), and Effort (E) for each class of lever to secure maximum marks.

 

Use Your Brain Power. (Textbook Page No. 199)

 

Question 1. Why are long bones slightly bent and not straight?
Answer:
1. Long bones include tibia, fibula, femur, humerus, radius, ulna, etc.
2. They have greater length than width. They consist of a shaft and variable number of epiphysis.
3. They are slightly bent or curved to absorb the stress of the body’s weight and evenly distribute the body weight at several different points. This structural curvature acts like a natural shock absorber for our daily movements.
4. If long bones were straight, the weight of the body would be unevenly distributed and the bone would fracture more easily.
In simple words: Long bones are slightly curved so they can support our body weight without breaking. If they were completely straight, they would snap easily under pressure.

🎯 Exam Tip: Mention both weight distribution and shock absorption to secure full marks in this question.

 

Identify and Label (Textbook Page No. 199)

 

Question 1. Identify the different bones.
Answer: The different bones of the human skeleton shown in the diagram are:
• Cranium
• Clavicle
• Scapula
• Sternum
• Ribs
• Humerus
• Vertebral column
• Pelvic girdle
• Ulna
• Radius
• Carpals
• Metacarpals
• Phalanges
• Femur
• Patella
• Tibia
• Fibula
• Tarsals
• Metatarsals
These bones work together to provide structure, protection, and mobility to the human body.
In simple words: The human skeleton is made up of many different bones, like the skull (cranium), ribs, spine (vertebral column), and leg bones (femur, tibia, fibula), which protect our organs and help us move.

🎯 Exam Tip: Practice labeling the major bones like the femur, humerus, and cranium, as these are frequently asked in exams.

Identify and Label (Textbook Page No. 200)

 

Question 1. Name A, B, C and D from the given figure and discuss in group.
Answer:
A – Coronal suture
B – Sagittal suture
C – Lambdoidal suture
D – Lateral / Squamous suture

The skull has many sutures (type of immovable joints) present, out of which four prominent ones are:
1. Coronal suture: Joins frontal bone with parietals.
2. Sagittal suture: Joins two parietal bones.
3. Lambdiodal suture: Joins two parietal bones with occipital bone.
4. Lateral/squamous sutures: Joins parietal and temporal bones on lateral side. These specialized joints ensure that the delicate brain tissue remains securely protected within the cranial cavity.
In simple words: Sutures are tight, immovable joints that lock the bones of our skull together like puzzle pieces to protect our brain.

🎯 Exam Tip: Remember the specific bones joined by each suture, as examiners often ask which bones are connected by the coronal or sagittal sutures.

 

Can You Tell? (Textbook Page No. 201)

 

Question 1. Give schematic plan of human skeleton.
Answer: The human skeleton consists of 206 bones and is broadly divided into two main parts:
1. Axial Skeleton (80 bones): It forms the central axis of the body and includes the skull, vertebral column, ribs, and sternum.
2. Appendicular Skeleton (126 bones): It includes the bones of the limbs (arms and legs) and the pectoral and pelvic girdles that connect them to the axial skeleton. This structural division allows for both excellent protection of vital organs and a wide range of body movements.
In simple words: The human skeleton is divided into the axial skeleton, which forms the central core like the skull and spine, and the appendicular skeleton, which includes our arms, legs, and shoulder/hip joints.

🎯 Exam Tip: Memorize the total bone counts for both the axial (80) and appendicular (126) skeletons, as these numbers are frequently asked in multiple-choice questions.

 

Question 1. Give schematic plan of human skeleton.
Answer:
The human skeletal system consists of 206 bones and is divided as follows:
• Human Skeletal System (206)
    • Axial Skeleton (80)
        • Skull (22)
            - Cranium (8) [Median (4): Frontal (1), Occipital (1), Sphenoid (1), Ethmoid (1); Paired (2): Parietal (2), Temporal (2)]
            - Facial bones (14) [Nasal bones (2), Maxillae (2), Zygomatic (2), Mandible (1), Lacrimal bones (2), Palatines (2), Inferior nasal conchae (2), Vomer (1)]
        • Ear ossicles 2 × (3)
        • Hyoid (1)
        • Vertebral Column (26) [Cervical (7), Thoracic (12), Lumbar (5), Sacrum (1-fused), Coccyx (1-fused)]
        • Thoracic cage (25)
            - Ribs (24) [True ribs (7 pairs), Vertebrochondral / False ribs (\(8^{th}\), \(9^{th}\) and \(10^{th}\) pairs of ribs), Floating ribs (\(11^{th}\) and \(12^{th}\) pair)]
            - Sternum (1)
    • Appendicular Skeleton (126)
        • Bones of Limbs (120)
            - Forelimbs (Each 30) [Humerus (1), Radius (1), Ulna (1), Carpals (8), Metacarpals (5), Phalanges (14)]
            - Hind limbs (Each 30) [Femur (1), Patella (1), Tibia (1), Fibula (1), Tarsals (7), Metatarsals (5), Phalanges (14)]
        • Girdles (6)
            - Pectoral (4) [Scapula (2), Clavicle (2)]
            - Pelvic (2) [Coxal bone / Hip bones (2) (Made up by fusion of Ilium, Ischium, Pubis)]
In simple words: The human skeleton is divided into two main parts: the axial skeleton (80 bones) which forms the central axis of the body like the skull and spine, and the appendicular skeleton (126 bones) which includes our limbs and girdles.

🎯 Exam Tip: Memorize the division of bones into Axial (80) and Appendicular (126) groups, as this classification is frequently asked in exams along with the counts of specific bones like cranial and facial bones.

[Note: Numbers in the bracket indicate the number of bones.]

Can You Tell? (Textbook Page No. 201)

 

Question 1. Enlist the bones of cranium.
Answer: Cranium: It is made up of four median bones and two paired bones, which together form a protective helmet for the brain. These bones are tightly fused together in adults to ensure maximum structural integrity.
1. Frontal bone: It is median bone (unpaired) forming forehead, roof of orbit (eye socket) and the most anterior part of cranium. It is connected to two parietals, sphenoid and ethmoid bone.
2. Parietal bones: These paired bones form the roof of cranium and greater portion of sides of the cranium.
3. Temporal bones: These paired bones are situated laterally just above the ear on either side. Each temporal bone gives out zygomatic process that joins zygomatic bone to form zygomatic arch. Just at the base of zygomatic process is mandibular fossa, a depression for mandibles (lower jaw bone) that forms the only movable joint of the skull. This bone harbors the ear canal that directs sound waves into the ear. The processes of temporal bones provide points for attachment for various muscles of neck and tongue.
4. Occipital bone: It is a single bone present at the back of the head. It forms the posterior part and most of the base of cranium. The inferior part of this bone shows foramen magnum, the opening through which medulla oblongata connects with spinal cord. On the either sides of foramen magnum are two prominent protuberances called occipital condyles. These fit into the corresponding depressions present in 1st vertebra.
5. Sphenoid bone: Median bone present at the base of the skull that articulates with all other cranial bones and holds them together. This butterfly shaped bone has a saddle shaped region called sella turcica. In this hypophyseal fossa, the pituitary gland is lodged.
6. Ethmoid bone: This median bone is spongy in appearance. It is located anterior to sphenoid and posterior to nasal bones. It contributes to formation of nasal septum and is major supporting structure of nasal cavity.
In simple words: The cranium is the bony case that protects our brain. It is made of six different types of bones (some single, some in pairs) that fit together like a puzzle to form the skull.

🎯 Exam Tip: Clearly distinguish between paired (parietal, temporal) and unpaired (frontal, occipital, sphenoid, ethmoid) bones, and mention key landmarks like the foramen magnum and sella turcica to score full marks.

 

Question 1. Write a note on structure and function of skull.
Answer:
i. Structure of skull:
Skull is made up of 22 bones. It is located at the superior end of vertebral column. The bones of skull are joined by fixed or immovable joints except for jaw. These bones provide essential protection for the brain and support the sensory organs of the face.
Skull consists of cranium or brain box and facial bones.

i. Cranium: It is made up of four median bones and two paired bones.
1. Frontal bone: It is median bone (unpaired) forming forehead, roof of orbit (eye socket) and the most anterior part of cranium. It is connected to two parietals, sphenoid and ethmoid bone.
2. Parietal bones: These paired bones form the roof of cranium and greater portion of sides of the cranium.
3. Temporal bones: These paired bones are situated laterally just above the ear on either side. Each temporal bone gives out zygomatic process that joins zygomatic bone to form zygomatic arch. Just at the base of zygomatic process is mandibular fossa, a depression for mandibles (lower jaw bone) that forms the only movable joint of the skull. This bone harbors the ear canal that directs sound waves into the ear. The processes of temporal bones provide points for attachment for various muscles of neck and tongue.
4. Occipital bone: It is a single bone present at the back of the head. It forms the posterior part and most of the base of cranium. The inferior part of this bone shows foramen magnum, the opening through which medulla oblongata connects with spinal cord. On the either sides of foramen magnum are two prominent protuberances called occipital condyles. These fit into the corresponding depressions present in 1^st vertebra.
5. Sphenoid bone: Median bone present at the base of the skull that articulates with all other cranial bones and holds them together. This butterfly shaped bone has a saddle shaped region called sella turcica. In this hypophyseal fossa, the pituitary gland is lodged.
6. Ethmoid bone: This median bone is spongy in appearance. It is located anterior to sphenoid and posterior to nasal bones. It contributes to formation of nasal septum and is major supporting structure of nasal cavity.
In simple words: The skull is made of 22 bones that protect our brain and form our face. Except for the lower jaw, all these bones are tightly locked together and cannot move.

🎯 Exam Tip: Remember that the skull has 22 bones in total, divided into cranial and facial bones, and only the lower jaw (mandible) is movable. Mentioning the 'foramen magnum' and 'sella turcica' will help you secure full marks.

Facial Bones

Fourteen facial bones give a characteristic shape to the face. The growth of face stops of the age of 16.
Following bones comprise the facial bones:

1. Nasals: These are paired bones that form the bridge of nose.
2. Maxillae: These form the upper jaw bones. They are paired bones that join with all facial bones except mandible. Upper row of teeth are lodged maxillae.

Lateral View of Skull (Diagram Labels)

• Frontal bone
• Sphenoid bone
• Nasal bone
• Ethmoid bone
• Lacrimal bone
• Zygomatic bone
• Maxilla
• Mandible
• Parietal bone
• Temporal bone
• Occipital bone
• Mastoid process

3. Palatines: These are paired bones forming the roof of buccal cavity or floor of the nasal cavity.
4. Zygomatic bones: They are commonly called as cheek bones.
5. Lacrimal bones: These are the smallest amongst the facial bones. These bones form the medial wall of each orbit. They have lacrimal fossa that houses lacrimal sacs. These sacs gather tears and send them to nasal cavity.
6. Inferior nasal conchae: They form the part of lateral wall of nasal cavity. They help to swirl and filter air before it passes to lungs.
7. Vomer: The median, roughly triangular bone that forms the inferior portion of nasal septum.
8. Mandible: This median bone forms the lower jaw. It is the largest and strongest facial bone. It is the only movable bone of skull. It has curved horizontal body and two perpendicular branches i.e. rami. These help in attachment of muscles. It has lower row of teeth lodged in it.

 

Functions of Skull

Internet My Friend (Textbook Page No. 201)

 

Question 1. Cleft palate and cleft lip
Answer:
1. Cleft palate and cleft lip are the birth defects that occur when a baby’s lip or mouth does not develop properly.
2. Cleft palate happens when the tissue that forms the roof of the mouth does not join together completely during pregnancy.
3. Cleft lip happens when the tissue that makes up the lip does not join completely before birth. This leads to formation of an opening in the upper lip. These conditions can usually be corrected with surgery early in a child's life.
In simple words: Cleft lip and cleft palate are openings or splits in the upper lip or the roof of the mouth that happen when a baby is growing before birth.

🎯 Exam Tip: Clearly distinguish between cleft lip (affecting the lip) and cleft palate (affecting the roof of the mouth) to score full marks.

Can You Tell? (Textbook Page No. 202)

 

Question 1. Why skull is important for us? Enlist few reasons.
Answer:
Functions of skull:
1. It protects the brain.
2. It provides sockets for ear, nasal chamber and eyes.
3. Mandible bone of the skull helps in opening and closing of the mouth. Additionally, it gives shape and structure to our face.
In simple words: The skull is like a hard helmet that protects our brain and holds our eyes, ears, and nose in place while helping us chew.

🎯 Exam Tip: Remember to mention the mandible (lower jaw) as the only movable bone in the skull that helps in chewing and speaking.

Internet My Friend (Textbook Page No. 202)

 

Question 1. Find out information about sinuses present in skull, functions of skull and disorder
Answer: Sinuses are air-filled cavities located within the bones of the skull, specifically around the nasal cavity.
Functions of sinuses:
1. They decrease the weight of the skull.
2. They help in resonating the voice.
3. They produce mucus that moisturizes the nasal passages.
Disorders of sinuses:
1. Sinusitis: Inflammation or infection of the sinuses, causing congestion and pain. Proper hydration and steam inhalation can often help relieve mild sinus congestion.
In simple words: Sinuses are hollow spaces in our skull bones that make our head lighter and help clear our nasal passages.

🎯 Exam Tip: When writing about sinuses, highlight their main function of reducing skull weight and the common disorder called sinusitis.

Question. Write a note on 'sinusitis'.
Answer: Sinuses are the hollow cavities present in the skull. They humidify the air we breathe. These air-filled spaces also help in reducing the overall weight of the skull so we can hold our head up easily.
(i) The four types of sinuses present in the skull:
• Frontal sinuses: They are located above each eye. There are right and left frontal sinuses.
• Maxillary sinuses: They are the largest among all sinuses, located just behind the cheekbones near to upper jaws.
• Sphenoid sinuses: These are present just behind the nose.
• Ethmoid sinuses: These are present between the eyes.
(ii) Functions of skull:
• It protects the brain.
• It provides sockets for ear, nasal chamber and eyes.
• Mandible bone of the skull helps in opening and closing of the mouth.
(iii) Sinusitis: It is the inflammation of tissue lining the sinuses. Healthy sinuses when get blocked with mucus and germs causing infection which may lead to sinusitis. [Students are expected to find more information about sinusitis, using the internet.]
In simple words: Sinuses are empty spaces in our skull bones that moisten the air we breathe. If these spaces get blocked by mucus and germs, they get swollen and infected, which is called sinusitis.

🎯 Exam Tip: Memorize the locations of the four types of sinuses (frontal, maxillary, sphenoid, and ethmoid) as they are frequently asked in diagram-based or short-answer questions.

 

Something Interesting (Textbook Page No. 202)

 

Question 1. If police suspect strangulation, they carefully inspect hyoid bone and cartilage of larynx. These get fractured during strangulation. Various such investigations are done in case of suspicious death of an individual where ossification of sutures in skull, width of pelvic girdle, etc. are examined to find out approximate age of victim or gender of victim, etc. You may find out information about forensic science.
Answer: Forensic science is the application of scientific knowledge and methodology to criminal and civil laws, mainly during criminal investigation. Forensic scientists analyze physical evidence from crime scenes to help solve crimes. Forensic anthropologists and pathologists use skeletal remains to determine vital details about a deceased individual:
• Hyoid Bone and Larynx Cartilage: A fractured hyoid bone or thyroid cartilage strongly indicates manual strangulation or hanging, as these delicate structures in the neck easily break under external pressure.
• Sutures of the Skull: The joints (sutures) between skull bones gradually fuse (ossify) as a person grows older. By examining the extent of this fusion, forensic experts can estimate the approximate age of the victim at the time of death.
• Pelvic Girdle: The pelvis is the most reliable skeletal indicator of biological sex. Females have a wider, shallower pelvic cavity and a broader sciatic notch to facilitate childbirth, whereas males have a narrower, deeper pelvis.
• Forensic Odontology: Examination of dental remains helps in identifying individuals when other body parts are damaged beyond recognition, as teeth are highly resistant to decay.
Forensic scientists use these skeletal clues to reconstruct the biological profile of an unidentified individual.
In simple words: Forensic science uses scientific methods to solve crimes. By studying bones like the skull, pelvis, and neck bones, experts can find out how a person died, how old they were, and whether they were male or female.

🎯 Exam Tip: When writing about forensic science, highlight key skeletal indicators like the hyoid bone for strangulation, skull sutures for age estimation, and the pelvic girdle for gender determination to score full marks.

Forensic science is an application of science which is used in the matter of criminal determination and civil law. It is generally used in investigation of crimes. Forensic scientists collect, preserve and analyze the evidence during the course of investigation.

[Students are expected to find more information about forensic science on internet.]

Try This (Textbook Page No. 202)

 

Question 1. Feel your spine (vertebral column). Is it straight or curved?
Answer: Our spine shows four slight curves which are visible when viewed from the sides. These curves help us maintain balance while standing upright.
In simple words: Our spine is not perfectly straight like a ruler. It has four gentle curves that help us stand, walk, and balance easily.

🎯 Exam Tip: Remember that the human spine has four distinct curves, which are essential for maintaining an upright posture and balance.

 

Question 2. Find information about slipped disc. (Textbook page no.202)
Answer:
1. The bones of vertebral column are supported by the intervertebral discs.
2. These intervertebral discs act as shock absorbers due to which they are constantly compressed.
3. The disc consists of two parts – soft gelatinous inner part (nucleus pulposus) and tough outer ring.
If the ligaments of the intervertebral discs become injured, the pressure developed in the nucleus pulposus protrudes posteriorly or into one of the adjacent vertebrae. This is known as slipped disc. This condition can cause severe pain and limit movement.
[Students are expected to find more information using the internet.]
In simple words: The spine has soft cushions called discs between the bones. If these cushions get damaged or slip out of place, they press on nearby nerves and cause pain, which is called a slipped disc.

🎯 Exam Tip: Clearly define the role of intervertebral discs as shock absorbers and explain how injury to ligaments leads to a slipped disc.

Can You Tell? (Textbook Page No. 204)

 

Question 1. Write a note on curvatures of vertebral column and mention their importance.
Answer:
1. The four curvatures in human spine are cervical, lumbar, thoracic and sacral curvatures.
2. These natural curves make the spine highly flexible and strong, allowing it to support the weight of our entire upper body.
3. They act as natural shock absorbers when we walk, run, or jump, protecting the brain and spinal cord from sudden impacts.
In simple words: The four curves in our spine act like a spring. They help absorb shocks when we move and help us keep our balance while standing.

🎯 Exam Tip: List all four curvatures (cervical, thoracic, lumbar, sacral) and highlight their role in shock absorption and balance to score full marks.

 

Question 2. Explain the structure of typical vertebra.
Answer:
1. Each vertebra has prominent central body called centrum, which serves as the primary weight-bearing component.
2. The centra of human vertebrae are flat in anterio-posterior aspect. Thus, human vertebrae are amphiplatyan.
3. From the either side of the centrum are two thick short processes which unite to form an arch like structure called neural arch, posterior to centrum.
4. Neural arch forms vertebral foramen which surrounds the spinal cord.
5. Vertebral foramina of all vertebrae form a continuous ‘neural canal’. Spinal cord along with blood vessels and protective fatty covering passes through neural canal.
6. The point where two processes of centrum meet, the neural arch is drawn into a spinous process called neural spine.
In simple words: A typical vertebra consists of a main central body called the centrum and a bony arch called the neural arch. This arch forms a protective canal through which the spinal cord safely passes.

🎯 Exam Tip: When describing the structure of a vertebra, remember to highlight the role of the neural canal in protecting the spinal cord, as this is a key functional feature examiners look for.

Basic Plan of Vertebra (Diagram Labels)

• Spinous process (spine)
• Transverse process
• Lamina
• Pedicle
• Neural arch
• Vertebral foramen (neural canal)
• Centrum (body)
• Superior articular process
• Inferior articular process

Structure of Vertebra (Continued)

• 7. From the base of neural arch, two articulating processes called zygapophyses are given out on either side. The anterior is called superior zygapophyses and posterior called inferior zygapophyses.
• 8. In a stack of vertebrae, inferior zygapophyses of one vertebra articulates with superior zygapophyses of next vertebra. This allows slight movement of vertebrae without allowing them to fall.
• 9. At the junction of zygapophyses, a small opening is formed on either side of vertebra called intervertebral foramen that allows passage of spinal nerve.
• 10. From the base of neural arch, lateral processes are given out called transverse processes. Neural arch, neural spine and transverse processes are meant for attachment of muscles.

 

Question 2. How will you identify a thoracic vertebra?
Answer: Thoracic vertebrae can be identified on the basis of centrum, as the centrum of the thoracic vertebrae is heart shaped. This distinct anatomical shape helps differentiate it from other types of vertebrae.
In simple words: You can easily identify a thoracic vertebra because its main central part is shaped like a heart.

🎯 Exam Tip: Always highlight the "heart-shaped centrum" as the primary identifying feature of a thoracic vertebra to score full marks.

Can You Recall? (Textbook Page No. 206)

 

Question 1. How does humerus form ball and socket joint? Where is it located?
Answer: The rounded head of the humerus fits into the cup-like glenoid cavity of the pectoral girdle to form a highly movable ball and socket joint. This joint is located at the shoulder region, connecting the upper arm to the shoulder blade.
In simple words: The round top of your upper arm bone fits into a bowl-like socket in your shoulder, allowing you to swing your arm around in many directions.

🎯 Exam Tip: Be sure to mention both the "head of the humerus" and the "glenoid cavity of the pectoral girdle" to accurately describe how this joint is formed.

The head of humerus fits into the glenoid cavity of scapula and forms ball and socket joint. It is located in shoulder and hips.

Can You Tell? (Textbook Page No. 208)

 

Question 1. Differentiate between the skeleton of palm and foot.
Answer:

	Skeleton of palm	Skeleton of foot
a.	It consists of metacarpals and phalanges	It consists of metatarsals and phalanges
b.	Saddle joints and condyloid joints are in the palm.	Condyloid or saddle joints are not present the foot.

In simple words: The palm has metacarpals and flexible saddle joints that let us move our thumb, while the foot has metatarsals and lacks these highly flexible joints to keep our footing stable.

🎯 Exam Tip: Use a neat table to present differences clearly, highlighting key anatomical terms like metacarpals for hands and metatarsals for feet.

 

Question 2. Explain the longest bone in human body.
Answer: Femur: The thigh bone is the longest bone in the body. The head is joined to shaft at an angle by a short neck. It forms ball and socket joint with acetabulum cavity of coxal bone. The lower one third region of shaft is triangular flattened area called popliteal surface. Distal end has two condyles that articulate with tibia and fibula. This strong bone supports our entire body weight when we stand or run.

Parts of the Femur Bone:

• Greater trochanter
• Head
• Neck
• Lesser trochanter
• Shaft
• Lateral condyle
• Medial condyle

In simple words: The femur is our thigh bone, which is the longest and strongest bone in our body. It connects to our hip at the top and our knee at the bottom to help us walk and run.

🎯 Exam Tip: Remember to mention both the proximal end (head and neck forming the hip joint) and the distal end (condyles forming the knee joint) to get full marks.

Internet My Friend. (Textbook Page No. 212)

 

Question 1. Find out information about types of fractures and how they heal.
Answer: Fractures can be of various types such as simple (closed) where the bone breaks but doesn't pierce the skin, compound (open) where the bone pierces the skin, greenstick (partial fracture), and comminuted (bone breaks into multiple pieces). They heal through a natural process of bone remodeling, which begins with blood clotting (hematoma formation), followed by the growth of a soft cartilage callus, then a hard bony callus, and finally reshaping by specialized bone cells. This amazing self-repair mechanism ensures the bone regains its original strength over time.
In simple words: A fracture is a broken bone. The body heals it by first forming a blood clot around the break, turning it into soft cartilage, replacing it with hard bone, and finally smoothing it out.

🎯 Exam Tip: Clearly list the main types of fractures (like simple and compound) and outline the healing stages sequentially from hematoma to remodeling.

p>Fractures

• 1. Fractures are classified based on their severity, shape or position of the fracture line or the physician who first described them.
• 2. Types of fractures:
  • 1. Open fractures: The broken ends of the bone protrude through skin.
  • 2. Comminuted fractures: The bone is splintered, crushed or broken into pieces at the site of impact and smaller bone fragments lie between the two main fragments.
  • 3. Greenstick fractures: A partial fracture in which one side of the bone is broken and the other side bends.
  • 4. Impacted fractures: One end of the fractured bone is forcefully driven into the inferior of the other.
  • 5. Pott fractures: Fracture of the distal end lateral leg bone with serious injury of the distal tibial articulation.
  • 6. Codes fractures: Fracture of the distal end of the lateral forearm in which the distal fragment is displaced posteriorly.
• 3. A fractured bone heals in four phases viz, reactive phase, fibrocartilaginous formation phase, bony callus formation phase and bone remodeling phase.

[Source: Tortora, G., Derrickson, B. Principles of Anatomy and Physiology. 15^th Edition]

[Students are expected to find out more information about healing of fractures using the internet.]

Do You Remember? (Textbook Page No. 208)

 

Question 1. What are joints? What are the types?
Answer:
i. A point where two or more bones get articulated is called joint or articulation or athrosis. They are classified based on degree of flexibility or movement they permit into lastly synovial or freely movable or diarthroses type of joints. These connections are essential for both stability and skeletal movement.
ii. Synarthroses / fibrous joints / movable joints: In this joint, the articulating bones are held together by means of fibrous connective tissue. Bones do not exhibit movement. Hence, it is immovable or fixed.
In simple words: A joint is a place in the body where two or more bones meet. Some joints are completely fixed and cannot move, while others allow our skeleton to bend and move around.

🎯 Exam Tip: When defining joints, always mention their classification based on mobility (immovable, slightly movable, and freely movable) to secure full marks.

type of joint. Synarthroses are further classified into sutures, syndesmoses and gomphoses.

• Sutures: It is composed of thin layer of a dense fibrous connective tissue. Sutures are places of growth. They remain open till growth is complete. On completion of growth, they tend to ossify. Sutures may permit some moulding during childhood. Sutures are further classified into butt joint, scarf joint, lap joint and serrate joint.
• Syndesmoses: It is present where there is greater distance between articulating bones. At such locations, fibrous connective tissue is arranged as a sheet or bundle, e.g. Distal tibiofibular joint, interosseous membrane between tibia and fibula and that between radius and ulna.
• Gomphoses: In this type of joint, a cone shaped bone fits into a socket provided by other bone, e. g. Tooth and jaw bones.

Diagram Labels:

• Syndesmoses: Fibula, Tibia, Interosseous ligament, Ulna, Radius
• Gomphoses: Socket, Gomphosis, Periodontal ligament, Root of tooth

 

Iii. Cartilaginous / Slightly Movable Joints / Amphiarthroses

These joints are neither fixed nor freely movable. Articulating bones are held together by hyaline or fibrocartilages. They are further classified as:

• Synchondroses: The two bones are held together by hyaline cartilage. They are meant for growth. On completion of growth, the joint gets ossified, e.g. Epiphyseal plate found between epiphysis and diaphysis of a long bone, Rib – Sternum junction.
• Symphysis: In this type of joint, broad flat disc of fibrocartilage connects two bones. It occurs in mid-line of the body. e.g. Intervertebral discs, manubrium

 

Question 1. Explain Synchondroses with examples.
Answer: Synchondroses are a type of cartilaginous joint where the bones are joined by hyaline cartilage. Examples include the epiphyseal plates (found between the epiphysis and diaphysis of growing long bones), joints between ribs and sternum, and the pubic symphysis.

Diagram Labels for Synchondroses:

• Epiphyseal plates
• Epiphysis
• Diaphysis

In simple words: Synchondroses are joints made of cartilage that connect different parts of a bone or different bones, like the temporary growth plates in growing children.

🎯 Exam Tip: Always mention the epiphyseal plate as a key example of synchondrosis and note that it eventually ossifies (turns to bone) as a person matures.

 

Question 2. Describe the characteristics and structure of Synovial joints (freely movable joints / diarthroses).
Answer: Synovial joints (freely movable joints / diarthroses) are characterized by the following features:
1. It is characterized by presence of a space called synovial cavity between articulating bones that renders free movement at the joint.
2. The articulating surfaces of bones at a synovial joint are covered by a layer of hyaline cartilage. It reduces friction during movement and helps to absorb shock.
3. Synovial cavity is lined by synovial membrane that forms synovial capsule. Synovial membrane secretes synovial fluid.
4. Synovial fluid is a clear, viscous, straw coloured fluid similar to lymph. It is viscous due to hyaluronic acid. The synovial fluid also contains nutrients, mucous and phagocytic cells to remove microbes. Synovial fluid lubricates the joint, absorbs shocks, nourishes the hyaline cartilage and removes waste materials from hyaline cartilage cells (as cartilage is avascular). Phagocytic cells destroy microbes and cellular debris formed by wear and tear of the joint.

Diagram Labels for Synovial Joint:

• Ligament
• Bone
• Synovial cavity (contains synovial fluid)
• Articular (hyaline) cartilage
• Fibrous layer
• Synovial membrane
• Articular capsule

In simple words: Synovial joints are freely movable joints where bones are separated by a fluid-filled cavity. The synovial fluid acts as a lubricant to make movements smooth and painless.

🎯 Exam Tip: Clearly state the functions of synovial fluid—lubrication, shock absorption, and nourishment of cartilage—to score full marks in descriptive questions.

5. If the joint is immobile for a while, the synovial fluid becomes viscous and as joint movement starts, it becomes less viscous.

6. The joint is provided with capsular ligament and numerous accessory ligaments. The fibrous capsule is attached to periosteum of articulating bones. The ligament helps in avoiding dislocation of joint.

 

g. The types of synovial joints are on follows:

1. Pivot joint: In this type of joint, the rounded or pointed surface of one bone articulates with a ring formed partly by another bone and partly by the ligament. Rotation only around its own longitudinal axis is possible. e.g. in joint between atlas and axis vertebrae, head turns side ways to form ‘NO’ joint.

Diagram Labels:

• Odontoid process
• Transverse ligament
• Atlas
• Axis
• Pivot joint

 

2. Ball and socket joint: The ball like surface of one bone fits into cup like depression of another bone forming a movable joint. Multi-axial movements are possible. This type of joint allows movements along all three axes and in all directions. e.g. Shoulder and hip joint.

Diagram Labels:

• Pelvis
• Cartilage
• Head of femur
• Neck of femur
• Ball and socket joint

 

3. Hinge joint: In a hinge joint, convex surface of one bone fits into concave surface of another bone. In most hinge joints one bone remains stationary and other moves. The angular opening and closing motion (like hinge) is possible. In this joint only mono-axial movement takes place like flexion and extension. e.g. Elbow

🎯 Exam Tip: Be prepared to identify and label the parts of the pivot joint (like the atlas and axis) and the ball and socket joint (like the head of the femur and pelvis) as these diagrams are highly important for practical and theory exams.

... and knee joint.

Hinge Joint Diagram Labels:

• Humerus
• Tricep
• Cartilage
• Bicep
• Joint capsule (with synovial fluid)
• Radius
• Ulna

4. Condyloid Joint

It is an ellipsoid joint. The convex oval shaped projection of one bone fits into oval shaped depression in another bone. It is a biaxial joint because it permits movement along two axes viz, flexion, extension, abduction, adduction and circumduction is possible. e.g. Metacarpophalangeal joint.

Condyloid Joint Diagram Labels:

• Radius
• Ulna
• Articular cartilage
• Synovial membrane
• Ligament
• Synovial cavity
• Carpals

5. Gliding Joint

It is a planar joint, where the articulating surfaces of bones are flat or slightly curved. These joints are non-axial because the motion they allow does not occur along an axis or a plane. e.g. Intercarpal and intertarsal joints.

Saddle Joint

This joint is a characteristic of Homo sapiens. Here the articular surface of one bone is saddle-shaped and that of other bone fits into saddle (each bone forming this joint have both concave and convex areas). It is a modified condyloid joint in which movement is somewhat more free. It is a biaxial joint that allows flexion, extension, abduction, adduction and circumduction. e.g.

Carpometacarpellar Joint Between Carpal (Trapezium) and Metacarpal of Thumb

Imagine (Textbook Page No. 208)

 

Question 1. If your elbow joint would be a fixed type of joint and joint between teeth and gum would be freely movable.
Answer:
1. If the elbow joint would be fixed the flexion and extension of the forearm won’t be possible. Also, rotation of the forearm and wrist would not be not possible.
2. Gomphoses is the type of joint that holds the teeth in the jaw bone. If this joint would be freely movable, we would not be able to chew and all our teeth would fall out. This highlights how the structure of each joint is perfectly adapted to its specific function in our body.
In simple words: If our elbow couldn't move, we wouldn't be able to bend or rotate our arms, and if our teeth joints were loose, our teeth would simply fall out when we try to eat.

🎯 Exam Tip: Clearly distinguish between the functions of fixed joints and movable joints to score full marks.

Use Your Brain Power (Textbook Page No. 210)

 

Question 1. Why are warming up rounds essential before regular exercise?
Answer:
1. Warming up before exercise stimulates the production and secretion of synovial fluid which reduces the stress on joints during exercise.
2. Also, if a joint is immobile for a while, the synovial fluid becomes viscous and as joint movement starts, it becomes less viscous.
3. Warming up increases the blood circulation, loosening the joints and increasing the blood flow. It also prepares the muscles for physical activity. This gradual preparation helps prevent sudden injuries and muscle strains.
In simple words: Warming up helps lubricate our joints and increases blood flow, making our body flexible and ready for hard exercise.

🎯 Exam Tip: Mention the role of synovial fluid and blood circulation when explaining the importance of warming up.

Can You Tell? (Textbook Page No. 211)

 

Question 1. Classify various types of joints found in human body. Present the information in the form of chart. Give example of each type.
Answer:
i. A point where two or more bones get articulated is called joint or articulation or athrosis. They are classified based on degree of flexibility or movement they permit into lastly synovial or freely movable or diarthroses type of joints. This classification helps us understand how different parts of our skeleton move.
ii. Synarthroses / fibrous joints / immovable joints:
In this joint, the articulating bones are held together by means of fibrous connective tissue. Bones do not exhibit movement. Hence, it is immovable or fixed type of joint. Synarthroses are further classified into sutures, syndesmoses and gomphoses.
1. Sutures: It is composed of thin layer of a dense fibrous connective tissue. Sutures are places of growth. They remain open till growth is complete. On completion of growth, they tend to ossify. Sutures may permit some moulding during childhood. Sutures are further classified into butt joint, scarf joint, lap joint and serrate joint.
2. Syndesmoses: It is present where there is greater distance between articulating bones. At such locations, fibrous connective tissue is arranged as a sheet or bundle, e.g. Distal tibiofibular joint, interosseous membrane between tibia and fibula and that between radius and ulna.
3. Gomphoses: In this type of joint, a cone shaped bone fits into a socket provided by other bone,
In simple words: Joints are the places where our bones meet. Immovable joints, like the sutures in our skull, are packed tightly with tough fibers so that the bones cannot move at all, protecting our vital organs.

🎯 Exam Tip: To score full marks, clearly define synarthroses as immovable joints and list all three sub-types (sutures, syndesmoses, and gomphoses) with their specific examples.

e. g. Tooth and jaw bones.

Diagram: Fibrous Joints (Syndesmoses and Gomphoses)

• Syndesmoses: Fibula, Tibia, Interosseous ligament, Ulna, Radius
• Gomphoses: Socket, Gomphosis, Periodontal ligament, Root of tooth

 

iii. Cartilaginous / Slightly Movable Joints / Amphiarthroses:

These joints are neither fixed nor freely movable. Articulating bones are held together by hyaline or fibrocartilages. They are further classified as:

• Synchondroses: The two bones are held together by hyaline cartilage. They are meant for growth. On completion of growth, the joint gets ossified, e.g. Epiphyseal plate found between epiphysis and diaphysis of a long bone, Rib – Sternum junction.
• Symphysis: In this type of joint, broad flat disc of fibrocartilage connects two bones. It occurs in mid-line of the body. e.g. Intervertebral discs, manubrium and sternum, pubic symphysis.

Diagram: Synchondroses

• Epiphyseal plates
• Epiphysis
• Diaphysis

 

iv. Synovial Joints / Freely Movable Joints / Diarthroses:

1. It is characterized by presence of a space called synovial cavity between articulating bones that renders free movement at the joint.
2. The articulating surfaces of bones at a synovial joint are covered by a layer of hyaline cartilage. It reduces friction during movement and helps to

Structure and Types of Synovial Joints

Synovial Joint Diagram Labels:

• Ligament
• Bone
• Synovial cavity (contains synovial fluid)
• Articular (hyaline) cartilage
• Articular capsule:
  • Fibrous layer
  • Synovial membrane

 

Structure of Synovial Joint

3. Synovial cavity is lined by synovial membrane that forms synovial capsule. Synovial membrane secretes synovial fluid.

4. Synovial fluid is a clear, viscous, straw coloured fluid similar to lymph. It is viscous due to hyaluronic acid. The synovial fluid also contains nutrients, mucous and phagocytic cells to remove microbes.
Synovial fluid lubricates the joint, absorbs shocks, nourishes the hyaline cartilage and removes waste materials from hyaline cartilage cells (as cartilage is avascular). Phagocytic cells destroy microbes and cellular debris formed by wear and tear of the joint.

5. If the joint is immobile for a while, the synovial fluid becomes viscous and as joint movement starts, it becomes less viscous.

6. The joint is provided with capsular ligament and numerous accessory ligaments. The fibrous capsule is attached to periosteum of articulating bones. The ligament helps in avoiding dislocation of joint.

 

Types of Synovial Joints

g. The types of synovial joints are on follows:

1. Pivot joint: In this type of joint, the rounded or pointed surface of one bone articulates with a ring formed partly by another bone and partly by the ligament. Rotation only around its own longitudinal axis is possible. e.g. in joint between

1. Pivot Joint

Atlas and axis vertebrae, head turns side ways to form ‘NO’ joint.

Diagram Labels:

• Odontoid process
• Transverse ligament
• Atlas
• Axis
• Pivot joint

🎯 Exam Tip: Remember that the pivot joint allows for rotational movement, such as turning your head from side to side to say 'no'.

 

2. Ball and Socket Joint

The ball like surface of one bone fits into cup like depression of another bone forming a movable joint. Multi-axial movements are possible. This type of joint allows movements along all three axes and in all directions. e.g. Shoulder and hip joint.

Diagram Labels:

• Pelvis
• Cartilage
• Head of femur
• Neck of femur
• Ball and socket joint

🎯 Exam Tip: Always mention 'multi-axial movements' and 'all directions' when describing a ball and socket joint to score full marks.

 

3. Hinge Joint

In a hinge joint, convex surface of one bone fits into concave surface of another bone. In most hinge joints one bone remains stationary and other moves. The angular opening and closing motion (like hinge) is possible. In this joint only mono-axial movement takes place like flexion and extension. e.g. Elbow and knee joint.

Diagram Labels:

• Humerus
• Tricep
• Cartilage
• Bicep
• Joint capsule (with synovial fluid)
• Radius
• Ulna
• Hinge joint

🎯 Exam Tip: Clearly state that hinge joints allow only 'mono-axial' (one direction) movement, similar to the opening and closing of a door.

4. Condyloid Joint

It is an ellipsoid joint. The convex oval shaped projection of one bone fits into oval shaped depression in another bone. It is a biaxial joint because it permits movement along two axes viz, flexion, extension, abduction, adduction and circumduction is possible. e.g. Metacarpophalangeal joint.

Condyloid Joint Between Radius and Carpals (Diagram Labels):

• Radius
• Ulna
• Articular cartilage
• Synovial membrane
• Ligament
• Synovial cavity
• Carpals

 

5. Gliding Joint

It is a planar joint, where the articulating surfaces of bones are flat or slightly curved. These joints are non-axial because the motion they allow does not occur along an axis or a plane. e.g. Intercarpal and intertarsal joints.

 

Saddle Joint

This joint is a characteristic of Homo sapiens. Here the articular surface of one bone is saddle-shaped and that of other bone fits into saddle (each bone forming this joint have both concave and convex areas). It is a modified condyloid joint in which movement is somewhat more free. It is a biaxial joint that allows flexion, extension, abduction, adduction and circumduction. e.g. Carpometacarpellar joint between carpal (trapezium) and metacarpal of thumb.

Saddle Joint (Diagram Labels):

• Carpal (Trapezium)
• 1st Metacarpal

 

[Students are expected to prepare a chart on their own.]

 

Can You Tell? (Textbook Page No. 211)

 

Question 1. Human beings can hold an object in a better manner than monkeys. Why?
Answer:
1. Humans and monkeys both have five fingers including thumb, however humans can hold an object in better manner than monkeys because humans have highly developed opposable thumbs. The opposable thumb allows better grip. This unique anatomical feature gives humans a significant evolutionary advantage in tool-handling.
2. The saddle joint in thumb allows free and independent movement to the thumb the carpometacarpellar joint between carpal (trapezium) and metacarpal of thumb makes the thumb opposable. It allows biaxial movements, i.e. flexion - extension and adduction - abduction but not rotation.
[Note: Gorillas, chimpanzees, orangutans and some other variants of apes have opposable thumb.]
In simple words: Humans can grip things much better than monkeys because we have highly developed opposable thumbs. This thumb is supported by a special saddle joint that lets it move freely in different directions to hold objects tightly.

🎯 Exam Tip: Clearly mention the term 'opposable thumb' and the 'saddle joint' as these are key anatomical terms examiners look for.

 

Internet My Friend (Textbook Page No. 211)

 

Question 92. Now a days we hear from many elderly people that they are undergoing knee replacement surgery. Find out why one has to undergo knee replacement; how it is carried out and how it can be prevented.
Answer:
Knee replacement is done in following cases:
1. Osteoarthritis: The cartilage in the knee undergoes degradation. It is caused by many factors such as muscle weakness, aging, obesity, etc.
2. Rheumatoid arthritis: It is characterised by inflammation of the synovial membrane, where it starts secreting excess of synovial fluid in the joint. This fluid exerts extensive pressure on the joint and causes severe pain.
3. Post-traumatic arthritis: This is caused due to breakage of ligament or cartilage. The breakage can be due to severe injury or accident. It causes severe pain and requires knee replacement.
4. Procedure: The procedure involves removal of the damaged cartilage or ligament and replaces it with artificial implant made up of either metal, plastic or both. Regular low-impact exercise and maintaining a healthy weight can significantly help in preventing joint degeneration.
In simple words: People get knee replacements when their knee joints are badly damaged by aging, arthritis, or injuries, causing severe pain. During the surgery, doctors replace the worn-out joint parts with artificial ones made of metal or plastic.

🎯 Exam Tip: When explaining knee replacement, list the three types of arthritis clearly and briefly describe the surgical procedure to secure full marks.

Find Out (Textbook Page No. 212)

 

Question 1. You must have heard of Sachin Tendulkar suffering from ‘tennis elbow’, a cricketer suffering from a disorder named after another game. Can common people too suffer from this disorder? Find out more information about this disorder.
Answer: Yes, common people can also suffer from this disorder.
1. Tennis elbow is caused due to inflammation of tendon which joins muscles of forearm to the bone of upper arm (humerus). It is known as lateral epicondylitis.
2. It causes severe pain in the elbow. It occurs due to extensive repetitive movement of hand. This damages the tendon and increases the tenderness of the elbow joint.
3. This disorder develops not only in athletes but also in other common people whose job involves extensive movement of hand such as carpenter, painter, plumber, etc.
In simple words: Tennis elbow is a painful swelling of the tendons in the elbow caused by repeating the same hand movements over and over. Anyone whose job or hobby involves repetitive arm motions can get it, not just tennis players.

🎯 Exam Tip: Remember to mention the scientific name 'lateral epicondylitis' and list everyday professions like carpentry or painting to show that non-athletes are also affected.

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