Class 7 Science Skeleton System Notes

Skeletal system consists of a framework of bones and a few cartilages. Bone and cartilage are specialised connective tissues. In human beings, this system is made up of 206 bones and a few cartilages. It is grouped into two principal divisions – the axial and the appendicular skeleton.

Axial skeleton:-

Axial skeleton comprises of 80 bones distributed along the main axis of the body. The skull, vertebral column, sternum and ribs constitute axial skeleton. The skull is composed of two sets of bones cranial and facial, that totals to 22 bones. Cranial bones are 8 in number. They form the hard protective outer covering, cranium. The facial region is made up of 14 skeletal elements which form the front part of the skull. A single U-shaped bone called hyoid is present at the base of the buccal cavity and it is also included in the skull. Each middle ear contains three tiny bones – Malleus, Incus and Stapes, collectively called Ear Ossicles. The skull region articulates with the superior region of the vertebral column with the help of two occipital condyles (dicondylic skull)

Our vertebral column is formed by 26 serially arranged units called vertebrae and is dorsally placed. It extends from the base of the skull and constitutes the main framework of the trunk. Each vertebra has a central hollow portion (neural canal) through which the spinal cord passes. First vertebra is the atlas and it articulates with the occipital condyles. The vertebral column is differentiated into cervical (7), thoracic (12), lumbar (5), sacral (1-fused) and coccygeal (1-fused) regions starting from the skull. The number of cervical vertebrae are seven in almost all mammals including human beings. The vertebral column protects the spinal cord, supports the head and serves as the point of attachment for the ribs and musculature of the back. Sternum is a flat bone on the ventral midline of thorax. There are 12 pairs of ribs. Each rib is a thin flat bone connecteddorsally to the vertebral column and ventrally to the sternum. It has two articulation surfaces on its dorsal end and is hence called bicephalic.First seven pairs of ribs are called true ribs.Dorsally,they are attached to the thoracic vertebrae and ventrally connected to the sternum withthe help of hyaline cartilage. The 8th, 9th and10th pairs of ribs do notarticulate directly with the sternum but join the seventh rib with the help by hyalin cartilage.Thes are called vertebrochondral (false) ribs. Last 2 pairs (11th and 12th) of ribs are not connected ventrally and are therefore, called floating ribs. Thoracic vertebrae, ribs and sternum together form the rib cage.

Appendicular skeleton:-
The bones of the l imbs along with their girdles constitute the appendicular skeleton. Each limb is made of 30 bones. The bones of the hand (fore limb) are humerus, radius and ulna, carpals (wrist bones – 8 in number), metacarpals (palm bones – 5 in number) and phalanges (digits – 14 in number) . Femur (thigh bone – the longest bone), tibia and fibula, tarsals (ankle bones 7 in number), metatarsals (5 in number) and phalanges (digits – 14 in number) are the bones of the legs (hind limb) . A cup shaped bone called patella cover the knee ventrally (knee cap).

Pectoral and Pelvic girdle bones help in the articulation of the upper and the lower limbs respectively with the axial skeleton. Each girdle is formed of two halves. Each half of pectoral girdle consists of a clavicle and a scapula

Scapula is a large triangular flat bone situated in the dorsal part of the thorax between the second and the seventh ribs. The dorsal, flat, triangular body of scapula has a slightly elevated ridge called the spine which projects as a flat, expanded process called the acromion. The clavicle articulates with this. Below the acromion is a depression called the glenoid cavity which articulates with the head of the humerus to form the shoulder joint. Each clavicle is a long slender bone with the curvatures. This bone is commonly called the collar bone Pelvic girdle consists of two coxal bones. Each coxal bone is formed by the fusion of three bones – ilium, ischium and pubis. At the point of fusion of the above bones is a cavity called acetabulum to which the thigh bone articulates. The two halves of the pelvic girdle meet ventrally to form the pubic symphysis containing fibrous cartilage

Joints:
Joints are points of contact between bones, or between bones and cartilages. Force generated by the muscles is used to carry out movement through joints, where the joint acts as a fulcrum. Joints have been classified into three major structural forms, namely, fibrous, cartilaginous and synovial.

Fibrous joints do not allow any movement. This type of joint is shown by the flat skull bones which fuse end-to-end with the help of dense fibrous connective tissues in the form of sutures, to form the cranium. In cartilaginous joints , the bones involved are joined together with the help of cartilages. The joint between the adjacent vertebrae in the vertebral column is of this pattern and it permits limited movements.

Synovial joints are characterised by the presence of a fluid filled synovial cavity between the articulating surfaces of the two bones. Such an arrangement allows considerable movement. These joints help in locomotion and many other movements. Ball and socket joint (between humerus and pectoral girdle). Hinge joint (knee joint), Pivot joint (between atlas and axis), Gliding joint (between the carpals) and Saddle joint (between carpal and metacarpal of thumb) are some examples

Question: Which of the following is an example of an immovable joint?
a) Bones in the wrist
b) Bones in the face
c) Bones in the upper part of the skull
d) Bones in the shoulder
Answer: c

Question: The vertebral column is composed of _ _ ring like bones –
a) 33
b) 37
c) 39
d) 43
Answer: a

Question: Acetabulum is present in _ _ joint –
a) Hip
b) Knee
c) Elbow
d) Shoulder
Answer: a

Question: Pelvic girdle is present in –
a) Shoulder bone
b) Humerus
c) Thigh
d) None of these
Answer: d

Question: Total number of bones present in human skeleton is –
a) 23
b) 206
c) 207
d) 205
Answer: b

Question: The ends of two bones are connected by –
a) Muscles
b) Ligaments
c) Tendons
d) Calcified
Answer: b

Question: The number of floating ribs, in the human body, is –
a) 6 pairs
b) 5 pairs
c) 3 pairs
d) 2 pairs
Answer: d

Question: Where is the funny bone situated?
a) Elbow
b) Knees
c) Feet
d) Neck
Answer: a

Question: The skull is made up of –
a) 18 bones
b) 22 bones
c) 24 bones
d) 5 bones
Answer: b

Question: The total number of canines in the permanent dental set of human is –
a) 12
b) 8
c) 6
d) 4
Answer: d

Question: Bones require –
a) Calcium
b) Protein
c) Carbohydrate
d) Fats
Answer: a

Question: Our chest is enclosed by –
a) 8 pairs of ribs
b) 10 pairs of ribs
c) 12 pairs of ribs
d) 14 pairs of ribs
Answer: c

Question: Creature which has maximum number of ribs is –
a) Snake
b) Cow
c) Man
d) Dog
Answer: a

Question: Longest bone in our body is –
a) Tibia
b) Femur
c) Radius
d) Humerus
Answer: b

Question: Appendicular skeleton includes all except –
a) Hind limbs
b) Forelimbs
c) Vertebral column
d) Pectoral and pelvic girdles
Answer: c

Question: Which of the following components is a part of the pectoral girdle?
a) Ilium
b) Sternum
c) Acetabulum
d) Glenoid cavity
Answer: d

Question: Cranium of human contains a total of –
a) 8 bones
b) 12 bones
c) 14 bones
d) 20 bones
Answer: a

Question: The number of ring shaped bones in the vertebral column is –
a) 30
b) 206
c) 33
d) 36
Answer: c

Question: In man, the coccygeal bone is found in –
a) Skull
b) Pelvic girdle
c) Pectoral girdle
d) Vertebral column
Answer: d

Question: A person is able to sit squatting on the ground because of the presence of –
a) Ball and socket joints at knees
b) Ball and socket joints at hips
c) Sliding joints at hips
d) Immovable joints at hips
Answer: b

Question: Ball and socket joint is found in –
a) Knee
b) Shoulder
c) Foot
d) Elbow
Answer: b

Question: Which of the following is an example of Hinge joint?
a) Hip joint
b) Shoulder joint
c) Joints between bones of the backbone
d) Knee joint
Answer: d

Question: Tendons join –
a) Muscles to muscles
b) Bones to muscles
c) Bones to bones
d) None of the above
Answer: b

Question: Human bones are made up of –
a) Calcium
b) Phosphorous
c) Calcium & Phosphorous
d) Calcium & Magnesium
Answer: c