The human body has been regarded as a machine which has to do certain kinds of work or perform certain functions. These functions are: (i) Motion and locomotion (ii) Nutrition, which includes the digestion of food, respiration or breathing, the circulation of the blood etc. (iii) Reproduction in order to prevent the human race from becoming extinct and (iv) Regulation of these various functions by the nervous system Even the minute creation of the universe, which are composed of single cells, possess these characters in a greater or less degree.
Cell is the name given to the ultimate unit of living matter It is small particle of semi fluid living substance, the outer surface of which may sometimes become sufficiently firm to form limiting membrane or cell-wall.
The Human skeleton:
Man; formed by bones, flesh, skin, nerves and tissues. Bones form the basis of human physical structure. This frame work of bones is called skeleton. It is like a net work of bones on which flesh and skin are mounted there are about 206 bones that form this framework. For the purpose of description the skeleton may be divided into three portions, namely the bead, trunk and limbs.
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The Head or Skull:
This is the upper most part of the human skeleton. The entire structure of the head is known as ‘Skull. It is composed c f 22 bones, of which the ace contains 14. The skull forms a cavity for the protection of the brain, which is the most important part of the nervous system
The Trunk:
The trunk or the middle part of the body is formed by the spine or backbone, the ribs, the east, bone and the bones of the hips which help to from cavity called the pelvis.
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The spine is composed of 26 irregular bones .As it is made up to small bones called vertebrae, it is known as vertebral column. The spine forms a strong pillar for the support of the head, on which heavy weights are sometimes carried.
The small bones of which the spine is made are kept together by means of structures called muscles and ligaments. The structure of the spine is framed in such a manner that it enables the person to walk, bend the bodies d maintain an erect posture. For the protection of an important part of the nervous system connected with the rain, the spinal cord is contained within it.
The Ribs:
The 12 pairs of ribs arranged on either side f the breast-bone and that portion of the spine to which he ribs are attached is known as thorax or chest cavity. Ribs are made of flat bone and they are bow like in shape, like the bones of the skull, the rib bones are also net solid, he first set of seven pairs are connected with the breast- one by means of long pieces of cartilage which are called rue ribs.
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The next three are attached to each other by similar means and indirectly to the breast-bone which are known as false ribs. The last two pairs do not have any attachment with the other ribs and are therefore called Free Floating ribs Thus the chest wall have been constructed to give the maximum protection to the important structures contained in the chest cavity, namely the heart, lungs and large blood vessels connected with them.
The Limbs:
Limbs are essential parts of the body. The limbs consist of the arms and legs, and are spoken of as the upper and lower limbs. Each upper limb includes the shoulder blade, collar bone, arm, fore arm and hand.
The lower limb includes the haunch-bone, thigh bone, knee-cap leg and foot. The shoulder possesses great freedom of movement. The arm however possesses still greater freedom of movement, because the head of the arm bone or Homeruns round and works in a cup-shaped socket in the shoulder blade, thus forming a ball and socket joint.
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Therefore arm contains two bones called Radius and Ulna which helps the muscles attached to them. The wrist consists of eight small bones arranged in two rows are called Carpal bones.
The palm has five bones called Metacarpal bones. The fingers have fourteen bones altogether, arm which the thumb has two and others three bones are known as Phalangeal bones.
The haunch-bones are the strongest bones of the body, and form with the Sacrum, a cavity ea led the Pelvis, which means a basin. The weight of the body is supported chiefly by the haunch-bones with the thigh bones have a close relationship.
The thigh has a single bone (Femur), which is the longest and thickest one in the body. The leg contains two bones. (Tibia and Fibula) and the foot twenty six of which seven are called 1 tarsal, five Metatarsal a fourteen Phalangeal bones respectively. The lower limbs are used for the purpose of locomotion.
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Muscles:
Muscles from the fleshy portion of the body. It is by means of the muscles that one is able to stand, walk, run life weights and perform most of the ordinary acts of life. The muscles are of two types voluntary and involuntary.
The muscles which are directly under the control of the will such as those of the arras and legs are voluntary and the muscles of the heart are involuntary. Without one’s knowledge the movements in to heart are performed and the muscles which perform them have accordingly been called involuntary muscles. But the muscles of respiration are not entirely involuntary. It can be controlled to certain extent.
The act of respiration therefore both voluntary and involuntary. By the regular exercise the muscles are increased in size, while excessive use or disuse has the opposite effect.