Bones are the scaffolding on which the rest of the body hangs.
Together with cartilage, joints and muscles, they make up the musculoskeletal system.
The system is held together, giving shape to the body, by bands of fibrous tissue called
ligaments and tendons.
There are 206 bones, nearly 700 muscles, and about 250 joints in the human body.
Bones have an outer lining called periosteum, which contains many blood vessels,
nerves and lymphatic spaces. In the hollow interior of the bones is found bone marrow,
which is the principal blood forming organ. Muscles are the flesh of the body,
making up about 40 percent of its total weight. Their particular function is to move themselves
and move other parts of the body.
Skeleton: The human skeleton (Fig. 12) is made up of the skull (8 cranial and 14 facial bones),
the spinal column (7 Cervical vertebrae, 12 Thoracic vertebrae, 5 Lumber vertebrae, Sacrum
and Coccyx), the sternum (breastbone), the thorax (12 pairs of ribs), the pelvic girdle,
and the Limb(hand-humerus, radius, ulna, carpus and phalanges of toe).
Joints occur where the bones of the body fit together.
These are of three kinds :
1:- Immovable, like the joints between the bones of the skull
2:- Slightly movable, like the articulations of the vertebrae of the spine
3:- Freely movable, in certain directions, like the shoulder, elbow, wrist, finger
hip, knee, ankle and toe joints. The freely movable joints are of different mechanical types,
reflecting the movements required by them. Knees, fingers, wrist and toes, for example have
hinge joints. The hip and shoulder joints are of the ball and socket type.
Muscles: The function of the muscle cells is to contract in response to nervous stimuli.
The energy for this contraction is supplied by carbohydrates. The cycle of chemical operations
which bring about muscular contraction is extremely complex, the resulting mechanical
chains of which muscle protein is made up. Part of the energy of muscular activity is
dissipated as heat. The mechanical efficiency of muscle is about 25 percent.
|
