Spinal Cord Reflexes That Cause Muscle Spasm
In human beings, local muscle spasm is often observed. In many, if
not most, instances, localized pain is the cause of the local spasm.
Muscle Spasm Resulting from a Broken Bone. One type ofclinically
important spasm occurs in muscles that sur-round a broken bone. This results
from pain impulses initiated from the broken edges of the bone, which cause the
muscles that surround the area to contract tonically. Pain relief obtained by
injecting a local anes-thetic at the broken edges of the bone relieves the
spasm; a deep general anesthetic of the entire body, such as ether anesthesia,
also relieves the spasm. One of these two anesthetic procedures is often
necessary before the spasm can be overcome sufficiently for the two ends of the
bone to be set back into their appro-priate positions.
Abdominal Muscle Spasm in Peritonitis. Another type oflocal spasm
caused by cord reflexes is abdominal spasm resulting from irritation of the
parietal peritoneum by peritonitis. Here again, relief of the pain caused by
the peritonitis allows the spastic muscle to relax. The same type of spasm
often occurs during surgical operations; for instance, during abdominal
operations, pain im-pulses from the parietal peritoneum often cause the
abdominal muscles to contract extensively, sometimes extruding the intestines
through the surgical wound. For this reason, deep anesthesia is usually
required for intra-abdominal operations.
Muscle Cramps. Still another type of local
spasm is thetypical muscle cramp. Electromyographic studies indi-cate that the
cause of at least some muscle cramps is as follows: Any local irritating factor
or metabolic abnor-mality of a muscle, such as severe cold, lack of blood flow,
or overexercise, can elicit pain or other sensory signals transmitted from the
muscle to the spinal cord, which in turn cause reflex feedback muscle
contraction. The contraction is believed to stimulate the same sensory
receptors even more, which causes the spinal cord to increase the intensity of
contraction. Thus, pos-itive feedback develops, so that a small amount of
initial irritation causes more and more contraction until a full-blown muscle
cramp ensues.
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