Human skeleton, muscles, movement and posture. Part two. (1951)

g/b instructional presents muscles movement and posture the body is able to move its bony framework the skeleton contains a large number of slightly and freely movable joints movements of the body are brought about by the action of muscles the muscles which move the bones lie under the skin and form the flesh of the body these muscles are attached to the bones above then below the joint but live freely over the joint itself some muscles are attached to the bones by means of strong cords of white fibrous tissue called tendons these take up less room and concentrate the pull on a particular area of the bone these muscles are the three which act mainly on the elbow joint the biceps and brachialis muscles in front of the joint contract that is shortened to bend the elbow and raise the forearm the triceps muscle at the back of the limb contracts to straighten the forearm noticed that while the muscles in front are contracting that is shortening the back muscle must relax that is lengthen and that's when the back muscle is contracting the front muscles must relax all movements of the body are brought about by the contraction of the muscle or group of muscles with the corresponding relaxation of another muscle or group of muscles the relaxing muscle exerts a slight pull which studies the contracting muscle one group of muscles the muscles of restoration is continuously active alternately contracting and relaxing in order to breathe in the chest is enlarged and air passes down into the lungs in order to breathe out the chest returns to its original size and air is driven out of the lungs the inflation and deflation of the lungs depend on these movements of the Forex which alter its size the movements are brought about by the muscles of restoration the chief muscle used in breathing is the diaphragm a dome-shaped sheet of muscle with a central portion of fibrous tissue at the back the diaphragm is attached to the spine and the 12th ribs at the sides to the ribs which form the lower edge of the 4x and at the front to the sternum the diaphragm separates for 4x from the abdomen additional breathing muscles are the intercostal muscles which join the lower border of each rib to the upper border of the rib below it in breathing in the diaphragm contracts and descends thus enlarging the 4x from above downwards in breathing out the diaphragm relaxes and rises to its original position in breathing in the intercostal muscles also contract swinging the ribs upwards and outwards the sternum being carried forwards this enlarges the thorax from back to front and from side to side in breathing out both the intercostal muscles and the diaphragm relax the ribs and the diaphragm returning to their original positions here the same movements of the diaphragm and ribs are seen by means of x-rays notice the beating heart on each side of it you can also see some of the vessels carrying blood to and from the lungs in breathing out slight contraction of the abdominal muscles helps the assent of the relaxing diaphragm in breathing in the abdominal muscles relaxed as the diaphragm descends in this side view you can see very clearly the upward and outward movement of the ribs as you breathe in muscles not only execute movements but hold the body or parts of it indefinite position the most important for human beings is the erect position because the body has weight it has a tendency to fall when standing upright opposite groups of muscles are in a state of slight contraction to hold the bones in the required position notice these opposing groups in the upper trunk lower trunk upper leg and lower leg if the bones are in a good balanced position the muscles have little work to do and so do not easily tire when the trunk is moved out of a vertical position much greater muscular contraction is necessary to pull it back again watch the strong contraction of the muscles as the plank is pulled into the upright position the balance of the body has to be maintained not only when standing still but also during movement balance is maintained by the action of opposing groups of muscles at each step the trunk is left unsupported on the side of the leg which is moving forwards the muscles of the standing leg which is bearing the weight of the body contract to hold the pelvis firmly and prevent the trunk from falling to the unsupported side the feet play an important part in posture and in movement they have to bear the weight of the body and must be strong and flexible the weight of the body is borne by the heels and the balls of the toes the foot is arched between these points ligaments and muscles keep the small bones of the feet in a good position and allow free movement the body whether it is moving or at rest is supported by a jointed framework of bones the skeleton movement of the bones at the joints and the maintenance of posture are brought about by the action of muscles