Royal Army Medical Corps training pamphlet / War Office.

Date:
1944
Catalogue details

Licence: Public Domain Mark

Credit: Royal Army Medical Corps training pamphlet / War Office. Source: Wellcome Collection.

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    Muscles are fixed to bones in such a way that many different movements are possible. Fig. 13 shows the simple mechanical principle on which the elbow is bent or flexed by one muscle and straightened or extended by another. (When one of these muscles contracts, the other automatically relaxes). Besides bending and straightening, a turning movement (rotation) is eae ey TRICEPS x bending or straightening or FLEXING EXTENDING &» Fic. 13.—How THE Erspow JoINT 1s FLEXED BY THE BICEPS MUSCLE AND EXTENDED BY THE TRICEPS. also possible at the elbow and in many other joints, and by using the right muscles the arms can be drawn close to the hody or held away from it. In fact, thanks to the number and arrangement of its joints and muscles, the human body can perform with accuracy a very large variety of complicated movements. ; 36. Tendons.—In certain situations, such as the hands, ‘ these movements are facilitated by the formation of long leaders (tendons) through which the muscles exert their action from a distance. Sometimes these tendons run in grooves on the bone, which serve as bony pulleys, and often they lie in tendon sheaths containing fluid which prevents friction. Inflammation in tendon sheaths (known as tenosynovitis) is a not uncommon cause of pain in the wrist or ankle, and in such cases a finger placed over the painful spot can sometimes detect a grating caused by the tendon sticking to its sheath. 37. Muscular development.—Moderate exercise, together with good feeding, develops the muscles; disuse and poor feeding cause them to dwindle. . Great development of muscles is seen in persons who systematically exercise them. The effect of disuse in causing the dwindling or atrophy of muscles is particularly striking when a joint becomes very stiff or fixed ; the limb affected may decrease to half its proper breadth. When the nerves supplying muscles are damaged, the condition of the muscles thus rendered powerless can be preserved to a certain extent by massage and movement,