Handbook of the Hospital Corps, United States Navy, 1939 / published by the Bureau of Medicine and Surgery under the authority of the Secretary of the Navy.

Date:
1939
Catalogue details

Licence: Public Domain Mark

Credit: Handbook of the Hospital Corps, United States Navy, 1939 / published by the Bureau of Medicine and Surgery under the authority of the Secretary of the Navy. Source: Wellcome Collection.

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    it. The deep type is dense and tough and in addition to covering muscles, covers delicate and specialized structures such as organs and blood vessels. In many places sheets of it lie between adjacent groups of muscles thereby per- mitting the different groups to act independently and still remain in place. Each muscle has a nerve supply and it is usually through the action of its nerve that a muscle is brought into activity and its action coordinated with that of other muscles. Such a nerve is called a motor nerve and if one is destroyed by disease or injury the muscle usually becomes inactive and wastes away. In addition to the normal stimulation of muscles through their nerves, they may also be activated by mechanical, chemical, or electrical stimulation of the muscles themselves, and by the application of heat and cold. When a muscle contracts it uses a certain amount of energy to do a certain amount of work. In doing this work the protoplasm in the muscle cells breaks down and chemical waste products, which are toxic, are produced. If these waste products accumulate the phenomena of fatigue result, and in some cases muscular cramps may occur. To supply the energy required and restore the muscle protoplasm, carbohydrates are taken from the blood and oxidized in the muscle. During contraction, or work, carbon dioxide and water are formed by oxidation, and removed by the blood which also brings the oxygen necessary for the restoration of muscle protoplasm. In ordinary activities the blood Supply to muscles is increased, thereby increasing the supply of food materials, carrying away waste products more quickly, and enabling the muscles to build up and restore their efficiency. When muscle substance dies it becomes solid and rigid, and loses its power to react to stimulation. The stiffening and hardening of the muscles after death is due to this phenomenon, which is called rigor mortis. The muscles of the body are divided into the following groups: those of the head and face; of the neck; of the trunk, which is subdivided into those of chest, thorax, abdomen, back and perineum; those of the upper extremity ; and those of the lower extremity (fig. 20). The muscles of the head and face consist of numerous groups of small muscles which act in the movements of the eyes, the face, the scalp and assist in mastication, deglutition, talking and expression. The muscles of the neck move the head from side to side, backward and forward, and rotate it. Some of these muscles act as auxiliary muscles of respiration, assist in deglutition, in speaking, and in other complicated move- ments of the head and neck. The muscles of the back are divided into five layers, the superficial layer and four deep layers. They act on the spinal column to keep the trunk in an erect posture, and permit movements from side to side, forward and back- ward, and a moderate amount of turning. Those of the chest and thorax, including the diaphragm, the great muscle which separates the thoracic and the abdominal cavities, are chiefly respiratory muscles. -These muscles, with the exception of the diaphragm, assist in movements of the trunk, the neck and the upper extremities. The muscles of the abdomen are the ezternal oblique, the internal oblique, the rectus abdominis, and the transversus abdo- minis. The rectus abdominis is a paired muscle situated on each side of the median line of the abdomen within the fibrous aponeurosis of the oblique muscles. It extends from the symphysis pubis to the thoracic wall. These muscles form the sides and front of the abdominal wall. They assist in mictu- rition and defecation by compressing the abdominal viscerze. They also assist in respiration and emesis, flex the thorax on the pelvis and aid in lateral flexion and rotation of the spine.