b. Fatigue. Oxygen is used by the mitochondria of the muscle to produce
energy in the form of ATP.
(1) As a muscle is used, its oxygen supply becomes depleted. Naturally, this
depletion occurs more quickly in white striated muscle fibers than it does in red striated
muscle fibers. With continued exercise, however, the oxygen becomes depleted in both
types of fibers.
(2) However, ATP can still be formed, but much less efficiently, in a
sequence which is anaerobic (without oxygen). In this anaerobic sequence, the glucose
is only partially decomposed. The ultimate product of the anaerobic sequence is lactic
(3) Lactic acid accumulates in the sarcoplasm of the muscle fibers. As this
occurs, the muscle becomes stiffer and is no longer able to function well. This condition
is called fatigue. An oxygen debt has been built up during the anaerobic production of
ATP. This debt must be paid (the muscle must become replenished with oxygen)
before the muscle will be able to function properly again.
c. Tonus. Tonus is a state of semicontraction of the musculature of the body.
The degree of tonus varies considerably with the state of health and exercise of the
individual. Tonus serves to remove the slack from the skeletal muscles so they can act
immediately when called upon. Also, at the joints, tonus serves to keep the opposing
surfaces of the bones close together. This helps to prevent injury to the articular
cartilages during muscular contractions.
5-14. WOUND HEALING IN SKELETAL MUSCLES
After a skeletal muscle is injured, the wound area undergoes a specific series of
a. Special body cells collect in the area and remove dead and dying tissue. At
the margins of the wound, the healthy striated muscle fibers dedifferentiate (lose their
special character and become more simple in structure).
b. If damaged tissue and foreign materials have been properly removed
(debridement) and if the edges of the live muscle tissue are closely fitted to each other,
the regenerating muscle fibers will actually join and produce a whole muscle again.
c. If a great amount of muscle tissue is missing, a defect will remain in the
muscle. Some physicians have developed the "minced muscle" technique, used to
replace these defects.