NEET Biology Locomotion and Movement Notes

NEET Biology notes on Chapter 20 Locomotion and Movement cover movement and locomotion in animals, the structure of skeletal muscle fibre, the sliding filament theory of muscle contraction, muscle disorders, the human endoskeleton with the vertebral column and girdles, human joints as levers and common bone and joint disorders, with worked Check Point answers for revision.

CHAPTER 20: LOCOMOTION AND MOVEMENT

At a Glance

• Muscular tissue
• Structure of striated (skeletal) muscle
• Muscle contraction
• Osteology
• Human endoskeleton
  • Axial skeleton
  • Vertebral column
  • Sternum
  • Ribs
  • Appendicular skeleton
  • Arms
  • Legs
• Joints
• Human joints as levers
• Bones disorders

While going through the chapter pay special attention to the following:

Terms and Definitions: 1. Sarcomere 2. Muscle tetanus 3. Dicondylic skull 4. Sesamoid bone

Differences: 1. Movement and locomotion 2. Adductor muscles and abductor muscles 3. A-band and I-band 4. Red muscle fibres and white muscle fibres 5. Procoelous and heterocoelous centrum 6. Fibrous joint and cartilaginous joint

Joints: 1. Ball and socket joint 2. Pivotal joint 3. Immovable joint 4. Atlanto-occipital joint 5. Elbow joint as lever

Structures: 1. Muscle fasciculus 2. Cardiac muscle fibres 3. Shoulder girdle 4. Axis vertebra

Common names: 1. Calf muscles 2. Collar bone 3. Wish bone 4. Innominate bone 5. Cheek bone 6. Tongue bone 7. Wrist bones 8. Heel bone

Numbers: 1. Vertebrae in adults 2. Floating ribs 3. Skull bones 4. Ankle bones 5. Limb bones

Disorders: 1. Rheumatoidal arthritis 2. Sprain 3. Osteoporosis

Introduction

Movement is the characteristic of all living beings. Movement can occur at the cellular level, the organ level, or as movement of the entire body. The movement of the entire body is called locomotion.
Amoeba and Entamoeba move with the help of pseudopodia. Paramecium moves by cilia. The movement of sperms occurs by a flagellum (an enlarged version of a cilium) or a tail. The movement of macrophages and leucocytes (WBCs) are cellular movements in higher animals.
The movement of body parts, called kinesiology, includes the movement of jaws, eyeballs, gut (peristalsis), heart, lungs (breathing), limbs and appendages.
Locomotion enables animals to shift the entire body from one place to another, as in running, jumping, crawling, flying and swimming. Plants do not show locomotion (except a few lower plants), but they move body parts by phototropism or geotropism.

Advantages of Locomotion

1. Procuring nutrition.
2. Avoiding unfavourable conditions.
3. Finding shelter.
4. Defending against predators.
5. Searching for mating partners.

Locomotory Structures in Different Animal Groups

Porifera: the animals are sessile and have no locomotory structures. Only the larvae are free swimming.
Coelenterata: tentacles are present for movement. The epidermis and gastrodermis have epithelio-muscular and endothelio-muscular cells for locomotory movements, such as somersaulting and looping.
Annelida: longitudinal and circular muscles are differentiated. The animal moves with the help of parapodia (in Nereis) or setae (in earthworm). The locomotory structure in leech is the posterior sucker. The coelomic fluid acts as a hydrostatic skeleton.
Arthropoda: jointed appendages are used for locomotion. The chitin forms the exoskeleton and provides support to the muscles.
Mollusca: the foot is used for locomotion.
Echinodermata: the water vascular system (ambulacral system) is used for locomotion through tube feet.
Vertebrata: locomotion is carried out by skeletal muscles associated with the endoskeleton of the limbs.

Check Point 1

1. What are the locomotory structures in the following animals? (i) Entamoeba (ii) Paramecium (iii) Jelly fish (iv) Nereis (v) Euglena (vi) Earthworm (vii) Snail (viii) Planaria (ix) Sepia (x) Sea star

Answer:
(i) Entamoeba: pseudopodia.
(ii) Paramecium: cilia.
(iii) Jelly fish: tentacles and epitheliomuscular cells of the body wall.
(iv) Nereis: parapodia.
(v) Euglena: flagellum.
(vi) Earthworm: setae.
(vii) Snail: muscular foot.
(viii) Planaria: cilia on the epidermis, together with body muscles.
(ix) Sepia: fins and a muscular funnel for jet propulsion.
(x) Sea star: tube feet of the water vascular system.

Teacher's Note:
a) Protists use pseudopodia, cilia or flagella, while animals with a coelom use muscles and body appendages.
b) The jet propulsion of Sepia and the tube feet of the sea star are common examples in NEET questions.

Structure of Biceps (Skeletal) Muscle

The outermost connective tissue covering of a muscle is called epimysium, which surrounds many bundles of muscle fibres. Each bundle of muscle fibres, called a fasciculus, is surrounded by a connective tissue covering called perimysium. Inside each fasciculus, each muscle fibre is surrounded by a connective tissue covering called endomysium.

Structure of Muscle Fibre

In ordinary light, alternate dark and light transverse bands appear in the muscle fibrils. The dark band is about 1.5 µ wide and the light band is about 0.8 µ wide.
In polarised light, the dark band is anisotropic and is called the A-band, whereas the light band is isotropic and is called the I-band.
The A-band in the centre contains an outer H-band and an inner M-band.
The I-band in the centre contains a zig-zag line or band, called the Z-band or Krause membrane.
The distance between two adjacent Z-bands (Krause membranes) is called a sarcomere.
The sarcomere is the functional unit of muscular tissue. It includes one A-band and two halves of the I-band.

[Figure 20.1: Detailed structure of a muscle fibre, showing the striations, myofibrils, nucleus, Z-band or Krause membrane, I-band, H-band, M-band, A-band, sarcomere and thick and thin filaments.]

Labels in Fig. 20.1 (from top to bottom): muscle fibre with striation, myofibril and nucleus; one sarcomere of a myofibril with the A band and I band marked; sarcomere enlarged between two Z-bands (Z-band or Krause membrane) showing thick filament, thin filaments, I-Band, M-Band, H-Band and A-Band.

A-band

It contains both thick and thin protein filaments. Thick filaments have a larger diameter than thin filaments but are fewer in number. The H-band contains thick filaments only. The M-band, in the centre of the H-band, also contains thick filaments and is prominent because of their thickening.

I-band

It contains thin filaments only. These filaments have a smaller diameter than thick filaments but are more numerous.

Thick Filaments

Thick filaments contain myosin protein and are also called myosin filaments. Myosin is a contractile protein.
Each myosin molecule contains six polypeptide chains: two heavy chains and four light chains.
Both heavy chains are spirally twisted to form a double helical structure. One end of each heavy chain is folded to form a globular (tertiary) structure called the myosin head. Each molecule therefore has two heads. The rest of the double helical structure is called the tail. The four light chains are part of the heads, two in each head.
Albert Szent-Gyorgyi used trypsin to digest the myosin molecule into two parts: the anterior part with the heads, called heavy meromyosin (HMM), and the posterior part, called light meromyosin (LMM).
The heads of myosin act as hooks, forming cross-bridges with the active sites of actin. Each head also acts as an ATPase in the presence of Mg²⁺.
Thick filaments are present in the A-band only.

[Figure 20.2: Actin and myosin filaments. (1) Thick filament: myosin molecules with heads, tails and light chains; digestion by trypsin gives light meromyosin (LMM) and heavy meromyosin (HMM). (2) Thin filament: G-actin monomers forming F-actin, with tropomyosin, troponin, actin binding sites, ATP-binding site and cross-arm sites.]

Thin Filaments

Thin filaments contain mainly actin protein, so they are called actin filaments. They also contain troponin and tropomyosin proteins.
The ratio between actin (~ 20%) and myosin (~ 55%) in muscles is 1:3.
Thin filaments are present in both the A-band and the I-band.
Actin is a fibrous protein and is of two types:
1. G-actin (globular actin): a monomer.
2. F-actin (fibrous actin): a polymer that takes part in the contraction process.
Troponin is a complex globular protein. It covers the active sites on tropomyosin. It has a high affinity for calcium. When Ca²⁺ binds to troponin, the active sites of the actin filament are exposed.
Tropomyosin is a fibrous, rod-shaped protein. It forms a double helix, and its two helical strands are coiled around F-actin.

Muscle Contraction

Huxley and Huxley (1954) described the sliding filament theory of muscle contraction. The main steps are:
1. In skeletal muscles, the nerve impulse reaches the neuromotor junction (motor end plate) and spreads through the T-tubule system. Two such systems are present in the muscle fibres of higher vertebrates and one in the fibres of lower vertebrates, such as the frog. The T-tubule system lies on either side of the sarcomere in the first case, and in the centre of the sarcomere in the second case.
2. At the neuromotor junction, acetylcholine, a common neurotransmitter, is released.
3. Acetylcholine stimulates the sarcoplasmic reticulum (a modified endoplasmic reticulum) to release calcium ions.
4. Calcium binds to specific sites on troponin.
5. The conformation of troponin, which has a high affinity for Ca²⁺, changes, and the active sites on actin are exposed.
6. The heads of the myosin filaments attach to the active sites, forming cross-bridges.
7. Because of cross-bridge formation, the thin filaments slide between the thick filaments, and the I-band becomes shorter.
8. Sliding continues, the H-band disappears, and later the I-band also disappears.
9. All sarcomeres show similar changes, and the whole muscle contracts.

[Figure 20.3: Diagrammatic representation of muscle contraction. (A) Cross-bridge formation between the myosin heads (HMM) and actin filaments, between Z-bands and across the M-band. (B) Sliding of actin filaments over myosin filaments, with the Z-bands moving closer together.]

Energy Metabolism

During aerobic conditions, muscle glycogen changes into glucose and then into pyruvic acid, which enters the Krebs cycle to release energy in the form of ATP. The ATP produced causes muscle contraction and is itself changed into ADP. Creatine phosphate (CP) changes ADP back into ATP: ADP + creatine phosphate → ATP + creatine.
During anaerobic respiration, muscle glycogen passes through glucose and pyruvic acid and changes into lactic acid. The lactic acid accumulates in muscles and produces muscle fatigue. The lactic acid passes through the blood to the liver. One-fifth of it is converted into CO₂ and H₂O, and four-fifths is changed into glucose, which returns to the muscles as muscle glycogen. This cycle, which describes the fate of lactic acid in the liver, is known as the Cori and Cori cycle.

[Figure 20.4: Cori and Cori cycle (lactic acid cycle). Muscle glycogen gives glucose and pyruvate in the muscle, which gives lactate; lactate passes through the blood to the liver, where four-fifths forms glucose and liver glycogen and one-fifth is oxidised to CO₂ and H₂O.]

Single Twitch and Tetanus

A single contraction of a muscle fibre is called a muscle twitch. A sustained contraction of the muscle is called muscle tetanus. Most of our day-to-day activities are due to muscle tetanus.

Check Point 2

1. Fill in the blanks, each with a suitable word or statement. (i) The structural and functional unit of muscles are ........ and ........ (ii) ........ are the proteins of thin filaments of muscle fibril. (iii) Krause membrane is present in the centre of ........ band. (iv) ........ band contains both thick and thin filaments. (v) The head of ........ protein also acts as ATPase. (vi) ........ of thin filaments has high affinity for Ca⁺⁺. (vii) The accumulation of ........ causes fatigue in muscles. (viii) Cori and Cori cycle is related to the fate of ........ (ix) ........ (neurotransmitter) is released at neuromotor junction. (x) The sustained contraction in muscles is called ........

Answer:
(i) Myofibril and sarcomere (the sarcomere is the functional unit, and the myofibril is the structural unit).
(ii) Troponin and tropomyosin.
(iii) I-band.
(iv) A-band.
(v) Myosin.
(vi) Troponin.
(vii) Lactic acid.
(viii) Lactic acid.
(ix) Acetylcholine.
(x) Muscle tetanus.

Teacher's Note:
a) Troponin is the protein that binds calcium and exposes the actin active sites.
b) Lactic acid causes fatigue, and the Cori cycle removes it from the muscle.

Muscular Disorders

1. Muscular dystrophy: The most common form is Duchenne muscular dystrophy. It is a genetic disorder. Its gene, dystrophin, is present on the X chromosome, and it is the longest gene (2,400 kbp) of the human genome. It causes degeneration of skeletal muscles, with weakness of muscles, loss of mobility and lack of coordination. There is no specific cure.
2. Myasthenia gravis: It is a chronic autoimmune disease that breaks down the neuromuscular junction, so the brain loses control over muscles. The synaptic cleft is widened, and the amount of acetylcholine and the number of receptors at the motor end plate decrease, so impulses are not transmitted effectively. It causes weakening of muscles, fatigue and later paralysis. Symptoms include drooping eyelids, difficulty in swallowing, muscle fatigue, difficult breathing and inability to control facial expressions. It can be controlled by medication or surgery.
3. Tetany: It is caused by low calcium concentration in the blood (hypocalcaemia), usually due to hyposecretion of PTH. It causes spasmic (sudden) contraction of muscles. Muscle tetany is different from muscle tetanus, which is a sustained contraction, and from bacterial tetanus (lock-jaw), which is caused by infection with Clostridium tetani.
4. Cramps: These are painful involuntary contractions of skeletal muscles, caused by salt imbalance, fatigue, stress or poor posture. They usually occur in the calf or thigh muscles, or in the hands, where they are called writer's cramps. A spasm is a sustained involuntary contraction of muscles.
5. Cerebral palsy: It is one of the most common congenital disorders. It affects the muscular system, so body posture, balance and motor functions are affected. Brain damage before or during birth causes loss of muscle tone, which makes routine physical tasks difficult for children.
6. Fatigue: It is tiredness due to prolonged muscular activity. It occurs due to dehydration (loss of water and salts) or the accumulation of metabolic wastes, such as lactic acid.

Human Endoskeleton

The total number of bones in an adult human endoskeleton is 206. It has two major parts:
1. Axial skeleton (forming the body axis): 80 bones.
2. Appendicular skeleton: 126 bones.

[Figure 20.5: Diagrammatic representation of the number of bones in the human skeleton, showing 80 axial and 126 appendicular bones.]

Axial Skeleton (80 bones)

It includes the skull (28), hyoid (1), vertebral column (26), sternum (1) and ribs (24).

Skull (28 bones)

Cranium (8 bones): frontal (1), parietal (2), temporal (2), occipital (1), ethmoid (1) and sphenoid (1).
Face (14 bones): maxilla (2), mandible (1), zygomatic (2), nasal (2), lacrimal (2), palatine (2), inferior conchae or turbinals (2) and vomer (1).
Ear (6 bones, 3 in each ear): malleus, incus and stapes in each ear.
The occipital bone contains the foramen magnum, through which the brain continues as the spinal cord. There are two occipital condyles, one on each side of the foramen magnum. Such a skull is called dicondylic. Mammals, and also amphibians such as the frog, have a dicondylic skull. The skulls of fishes, reptiles and birds are monocondylic, with a single occipital condyle on the ventral side of the foramen magnum.
The mandible is the only movable bone of the skull.
The zygomatic arch, also known as the cheek bone, is formed in the rabbit by a process of the squamosal, a complete jugal and a process of the maxilla. Its presence is a characteristic of all mammals.

[Figure 20.7: Bones of the skull, including frontal, parietal, sphenoid, temporal, ethmoid, nasal, lacrimal, zygomatic, maxilla, occipital, mastoid process and mandible, with the lambdoidal suture.]

Hyoid bone

It is also called the tongue bone. It is U-shaped and does not articulate with any other bone. It lies in the throat. Including it in the skull gives 28 + 1 = 29 skull bones.

Vertebral Column

The backbone has 26 vertebrae in adults and 33 in children. A typical vertebra has an amphiplatyan (acoelous) centrum, two transverse processes, a neural arch with a neural canal for the spinal cord, and a neural spine on the dorsal side. The articulating surfaces are called the prezygapophyses (anterior) and postzygapophyses (posterior).
Between adjacent vertebrae are tough intervertebral discs of fibrous cartilage. These discs provide flexibility. The central part of each disc is soft and is called the nucleus pulposus.

[Figure 20.8: Typical vertebra, showing the transverse process, neural spine, neural canal, articulating surface and centrum.]

Types of Centra (Connecting Concept)

The centrum is the solid part of the vertebra and develops from the embryonic notochord. The main types are:
1. Procoelous: concave in front and generally convex behind, as in the vertebrae of amphibians and reptiles.
2. Amphicoelous: concave on both surfaces, as in the vertebrae of fishes and the 8th vertebra of the frog.
3. Heterocoelous (saddle-shaped): each surface has a pair of concave and convex surfaces, as in the vertebrae of birds.
4. Acoelous: no concavity on either side, as in the 9th vertebra of the frog. It has a double convexity at the back.
In mammalian vertebrae, both surfaces of the centrum are flat. Such a centrum is better called amphiplatyan.

[Figure 20.9: Different types of centra: procoelous, amphicoelous, heterocoelous and amphiplatyan, with anterior and posterior surfaces labelled.]

Vertebral Column in Humans

Region, number in child and number in adult:
Cervical (neck): 7 in both.
Thoracic (chest): 12 in both.
Lumbar (abdomen): 5 in both.
Sacral (hip): 5 in child, fused into 1 (sacrum) in adult.
Caudal (tail): 4 in child, fused into 1 (coccyx) in adult.
Total: 33 in child and 26 in adult.
Vertebral formula: child C7 T12 L5 S5 Cd4; adult C7 T12 L5 S(1) Cd(1).

[Figure 20.10: The vertebral column, lateral view, showing 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, the sacrum and the coccyx.]

Cervical vertebrae (7)

Seven cervical vertebrae are a characteristic of mammals. The exceptions are sea cows (manatees), which have 6 to 9 neck vertebrae. The peculiar feature of cervical vertebrae is the foramen transversarium (vertebro-arterial canal) in the transverse processes, which carries the cervical arteries.
1st cervical vertebra, the atlas: transverse processes and neural spine reduced, centrum reduced, prezygapophyses absent. It has two facets that form the atlanto-occipital joint with the two occipital condyles of the skull. It has a foramen for the vertebral artery.
2nd cervical vertebra, the axis: the odontoid process (dens) projects from the anterior side of the centrum and forms a pivotal joint that lets the skull rotate. Both pairs of zygapophyses are present.
3rd to 7th cervical vertebrae: typical cervical vertebrae.

[Figure 20.11: Atlas, showing facets for the occipital condyles and the foramen for the vertebral artery.]

[Figure 20.12: Axis, showing the odontoid process, the facet for the atlas, the transverse process, the foramen for the vertebral artery and the body.]

Thoracic vertebrae (12)

These are the 8th to 19th vertebrae. Each has two pairs of facets for the attachment of ribs. Anterior thoracic vertebrae have longer neural spines, and posterior thoracic vertebrae have shorter ones.

[Figure 20.13: Thoracic vertebra, showing the neural spine, transverse process, facets for rib articulation, vertebral foramen and centrum.]

Lumbar vertebrae (5)

These are the 20th to 24th vertebrae. They are the biggest vertebrae of the backbone. Ribs are not attached to them, so there are no rib facets. They have extra articulating surfaces, the metapophyses (anterior) and anapophyses (posterior), for better movement.

[Figure 20.14: Lumbar vertebra, showing the neural spine, transverse process, articular processes, vertebral foramen and centrum.]

Sacral vertebrae (5, fused into the sacrum)

The 5 sacral vertebrae, the 25th vertebrae, are fused into one sacrum in adults. There are four pairs of foramina. A large facet on each side articulates with the ilium of the hip girdle.

Caudal vertebrae (4, fused into the coccyx)

The 4 caudal vertebrae, the 26th vertebrae, are fused into one coccyx in adults. Because humans have no tail, the coccyx is vestigial. Its transverse processes are rudimentary or absent.

[Figure 20.15: Sacrum (S1 to S5) and coccyx (C1 to C4), showing the foramina for nerves and the articulating surfaces.]

Sternum

The sternum (1 bone) is the breastbone. It is single and has three parts: the manubrium, the body of the sternum and the xiphoid process. The xiphoid process gives attachment to the diaphragm.

Ribs (12 pairs)

The ribs are attached dorsally to the vertebral column and ventrally to the sternum.
1. True ribs: 7 pairs (1st to 7th), attached directly to the sternum through intercostal cartilages.
2. False ribs: 3 pairs (8th to 10th), attached indirectly to the sternum through the intercostal cartilage of the 7th rib. They are also called vertebrochondral ribs.
3. Floating ribs: 2 pairs (11th and 12th), not attached to the sternum.

All ribs of mammals are double-headed (bicephalic), with a capitulum and a tuberculum attached to the thoracic vertebrae. In birds the ribs are also double-headed, but they have an uncinate process as well. In reptiles the ribs are single-headed. In frogs the ribs are absent.

[Figure 20.16: Sternum and ribs, showing the clavicle, manubrium, body of sternum, xiphoid process, costal cartilages and ribs 11 and 12.]

Appendicular Skeleton (126 bones)

It includes the bones of the pectoral and pelvic girdles and the bones of the arms and legs.
Pectoral girdle: 4 bones (2 + 2).
Arms: 60 bones (30 + 30).
Pelvic girdle: 2 bones (1 + 1).
Legs: 60 bones (30 + 30).

Pectoral (shoulder) girdle

Each half of the pectoral girdle has two bones, the clavicle (collar bone) and the scapula. The acromion process is a spine on the scapula for articulation with the clavicle. The scapula, called the universal bone of the pectoral girdle, has a glenoid cavity for the articulation of the humerus. The coracoid process is also formed from the scapula.

[Figure 20.17: Pectoral girdle (half), showing the spine, acromion process, coracoid process and glenoid cavity of the scapula.]

Arms (30 bones in each arm)

Upper arm: 1 bone, the humerus.
Lower arm: 2 bones, the radius and ulna.
Wrist: 8 carpal bones, 4 in each row.
Palm: 5 metacarpal bones.
Fingers: 14 phalanges.

Humerus

The head of the humerus articulates in the glenoid cavity of the pectoral girdle. A deltoid ridge in the middle of the humerus gives attachment to the biceps muscles. There is a bicipital groove. The distal end of the humerus articulates with the radius and ulna to form the elbow.

Radius and ulna

The radius lies towards the body axis and is shorter than the ulna. The ulna forms the olecranon process of the elbow. The radius and ulna together form the sigmoid notch at their proximal end.

Carpals

The carpals form two rows. The proximal row contains the scaphoid, lunate, triquetral and pisiform. The distal row contains the trapezium, trapezoid, capitate and hamate.

[Figure 20.18: Bones of the hand, showing the carpals, metacarpals (I to V), and proximal, middle and distal phalanges.]

Connecting Concept

In birds, the clavicles and the interclavicle are fused to form a fork-shaped bone called the furcula, or wishbone (bone of merry thoughts).

Pelvic (hip) girdle

Each half of the pelvic girdle is called the innominate bone (os innominatum) or coxal bone. It is formed by the fusion of three bones: the ilium, ischium and pubis. The obturator foramen is formed by the ischium and pubis. The acetabulum (cavity) is formed by all three bones, and the head of the femur articulates in it. The two innominate bones are joined at the pubis by fibrous cartilage, the pubic symphysis.

[Figure 20.19: Pelvic girdle (half), showing the ilium with iliac crest, acetabulum, ischium with ischial tuberosity, pubis, obturator foramen and pubic symphysis.]

Legs (30 bones in each leg)

Thigh: 1 bone, the femur.
Knee cap: 1 bone, the patella.
Shank: 2 bones, the tibia and fibula.
Ankle: 7 tarsal bones.
Sole: 5 metatarsal bones.
Toes: 14 phalanges.

Femur

The femur is the strongest, heaviest and longest bone of the human skeleton. Its head articulates in the acetabulum of the pelvic girdle. Two prominent processes, the trochanters, are present in the head region for muscle attachment.

Patella

The patella is a sesamoid bone formed by the ossification of a tendon.

Tibia and fibula

The tibia is stronger, whereas the fibula is a weak bone. In the frog, the tibia and fibula are fused to form the tibio-fibula, which is the longest bone of the frog's body.

Tarsals

The tarsals form three rows: 2 (talus and calcaneum) + 2 (navicular and cuboid) + 3 (cuneiform). The calcaneum is the longest tarsal and forms the heel of the foot.

[Figure 20.20: Bones of the foot, showing the talus, calcaneus, navicular, cuboid, three cuneiforms, five metatarsals and fourteen phalanges.]

Check Point 3

1. Match the structures of Column A with the name of the bones in Column B: Column A: (1) Acromian process (2) Deltoid ridge (3) Xiphoid process (4) Obturator foramen (5) Olecranon process. Column B: (a) Ulna (b) Femur (c) Coracoid (d) Scapula (e) Ribs (f) Sternum (g) Pelvic girdle (h) Humerus.

Answer:
(1) Acromian process: (d) Scapula.
(2) Deltoid ridge: (h) Humerus.
(3) Xiphoid process: (f) Sternum.
(4) Obturator foramen: (g) Pelvic girdle.
(5) Olecranon process: (a) Ulna.

Teacher's Note:
a) Options (b) femur, (c) coracoid and (e) ribs are distractors, because the coracoid belongs to the scapula and the femur is not part of either girdle in this match.
b) The olecranon process is the upper end of the ulna that forms the elbow.

Joints

Joints are of three types:
1. Fibrous (fixed) joints.
2. Cartilaginous (imperfect) joints.
3. Synovial (perfect) joints.

[Figure 20.21: (A) Fibrous joint, with fibrous connective tissue between the cranial bones. (B) Cartilaginous joint, with fibrous cartilage (intervertebral disc) between centra. (C) Synovial joint, with hyaline cartilage, synovial cavity containing synovial fluid, fibrous capsule, synovial membrane and periosteum.]

1. Fibrous joints (fixed or immovable, synarthroses): Fibrous connective tissue is present between the two bones. These joints are immovable. Examples are the joints of the cranial bones and the joints between the teeth and the jaw bones.
2. Cartilaginous joints (imperfect, amphiarthroses): Fibrocartilage is present between the two bones. These joints permit limited movement. Examples are the joints between mammalian vertebrae (through the intervertebral discs) and the pubic symphysis between the two innominate bones.
3. Synovial joints (perfect, diarthroses): Synovial fluid is present between the articulating bones. The bones have hyaline or articular cartilage. The synovial fluid is enclosed in the synovial membrane, in the synovial cavity.

Types of synovial joints

(i) Ball and socket joint: examples are the shoulder joint, the hip joint, and the joint between the incus and stapes of the ear. In the shoulder joint, the head of the humerus (ball) articulates in the glenoid cavity (socket). In the hip joint, the head of the femur (ball) articulates in the acetabulum (socket).
(ii) Hinge joint: examples are the elbow, knee and ankle joints, interphalangeal joints, and the joint between the malleus and incus of the ear. The elbow joint is formed between the humerus and the sigmoid notch of the radius and ulna. The knee joint is formed between the femur and the tibia-fibula. The ankle joint is formed between the tibia-fibula and the talus.
(iii) Saddle (condyloid) joint: examples are the wrist joint, the temporomandibular joint, the thumb joint, and the joint between the metacarpals and phalanges. This joint is also ball-and-socket type, but both the ball and socket are poorly developed, so free movement is not possible.
(iv) Pivotal joint: examples are the skull joint (not cranial joint) between the odontoid process of the axis vertebra and the atlas/skull, and the joint between the radius and ulna. At the radius and ulna, one end of the radius rotates around the ulna.
(v) Gliding (sliding) joint: examples are the intercarpal and intertarsal joints, the sternoclavicular joint, and the joint between the pre- and postzygapophyses of adjacent vertebrae.

Human Joints as Levers

1. Class I lever: example is the atlanto-occipital joint (up-and-down movement of the head). The skull acts as the weight (resistance), the joint acts as the fulcrum, and the effort is made by the neck muscles at the other end.
2. Class II lever: example is the toe joint, when the body rests on the toes. The weight of the body (resistance) lies in the centre.
3. Class III lever: example is the elbow joint. The effort, from the muscles that bend the forearm, lies in the centre.

[Figure 20.22: Types of levers, Class I, Class II and Class III, in the human skeleton, showing the fulcrum, effort and resistance, with the gastrocnemius and biceps muscles and the neck muscles marked.]

Bone and Joint Disorders

1. Osteoporosis: It is caused by hormonal imbalance, mainly of PTH or sex hormones, or by prolonged steroid treatment. It is an ageing disorder that makes bones porous and fragile.
2. Arthritis (joint disorders):
(i) Gout: salts of uric acid (sodium urate) are deposited in the joints, making movement stiff and painful. It is generally hereditary, as a sex-influenced, autosomal trait.
(ii) Osteoarthritis: an old-age disorder in which the hyaline cartilage is eroded.
(iii) Rheumatoid arthritis: an autoimmune disorder characterised by the presence of rheumatoid factor (immunoglobulin IgM). The synovial membrane becomes inflamed, and the amount of synovial fluid increases, causing pressure and pain. The thickened synovial membrane secretes abnormal granules, called pannus, which erode the cartilage. The fibrous tissue may ossify and make the joints immovable.
3. Fracture: a break in a bone, partial or complete. Types:
(i) Simple or closed: the broken ends do not protrude through the skin.
(ii) Compound or open: the broken ends pierce through the skin.
(iii) Transverse: the fracture is at right angles to the length of the bone.
(iv) Spiral: the fracture is spiral, or the bone is twisted.
(v) Greenstick: a partial fracture in which one side of the bone bends and the other side breaks. It occurs only in children.

Check Point 4

1. Write the type of joints against the name of the bones/bone parts. (i) Metacarpal and phalanges (ii) Humerus and radius-ulna (iii) Femur and acetabulum cavity (iv) Two pubis bones of pelvic girdle (v) Tibio-fibula and tarsals

Answer:
(i) Saddle (condyloid) joint.
(ii) Hinge joint (elbow joint).
(iii) Ball and socket joint.
(iv) Cartilaginous joint (pubic symphysis, amphiarthrosis).
(v) Hinge joint (ankle joint).

Teacher's Note:
a) Ball and socket joints allow movement in many directions, while hinge joints allow movement in one plane.
b) The pubic symphysis is a cartilaginous joint because it has fibrocartilage between the bones.

Check Point 5

1. Answer the following: (i) Which type of arthritis is an autoimmune disorder? (ii) In which disorder do the bones become porous and fragile? (iii) What is the difference between simple and compound fracture? (iv) What type of joint is present in cranial bones? (v) Which type of lever does the elbow joint represent? (vi) What is the difference between fibrous joint and fibrous cartilage joint? (vii) Which process of axis vertebrum forms the pivotal joint? (viii) What is the other name for cartilaginous joints? (ix) Which tarsal forms the heel of the foot? (x) In which type of arthritis do sodium urate crystals get deposited?

Answer:
(i) Rheumatoid arthritis.
(ii) Osteoporosis.
(iii) In a simple (closed) fracture, the broken ends do not protrude through the skin. In a compound (open) fracture, the broken ends pierce through the skin.
(iv) Fibrous (immovable) joints.
(v) Class III lever.
(vi) In a fibrous joint, fibrous connective tissue lies between the bones and the joint is immovable. In a fibrous cartilage joint, fibrocartilage lies between the bones and the joint permits limited movement.
(vii) The odontoid process (dens).
(viii) Amphiarthroses, or imperfect joints.
(ix) The calcaneum (calcaneus).
(x) Gout.

Teacher's Note:
a) Rheumatoid arthritis is autoimmune because the immune system attacks the synovial membrane.
b) The odontoid process of the axis forms the pivot on which the skull rotates.