Birth injuries, dislocations, vertebral fractures, stabs, gunshot wounds, and pressure from tumors can all injure spinal nerves. Suddenly bending the neck, called whiplash, can compress the nerves of the cervical plexuses, causing persistent headache and pain in the neck and skin, which the cervical nerves supply. If a broken or dislocated vertebra severs or damages the phrenic nerves associated with the cervical plexuses, partial or complete paralysis of the diaphragm may result.
Intermittent or constant pain in the neck, shoulder, or upper limb may result from prolonged abduction of the upper limb, as in painting or typing. This is due to too much pressure on the brachial plexus. This condition, called thoracic outlet syndrome, may also result from a con genital skeletal malformation that compresses the plexus during upper limb and shoulder movements.
Degenerative changes may compress an intervertebral disk in the lumbar region, producing sciatica, which causes pain in the lower back and gluteal region that can radiate to the thigh, calf, ankle, and foot. Sciatica is most common in middle-aged people, particularly distance runners. It usually compresses spinal nerve roots between L2 and S1, some of which contain fibers of the sciatic nerve. Rest, drugs, or surgery are used to treat sciatica.
In carpal tunnel syndrome, repeated hand movements, such as typing, inflame the tendons that pass through the carpal tunnel, which is a space between bones in the wrist. The swollen tendons compress the median nerve in the wrist, causing pain to shoot up the upper limb. Surgery or avoiding repetitive hand movements can relieve symptoms. ■
An important exception to the usual arrangement of sympathetic fibers occurs in a set of preganglionic fibers that pass through the sympathetic ganglia and extend out to the medulla of each adrenal gland. These fibers terminate within the glands on special hormone-secreting cells that release norepinephrine (20%) and epinephrine (80%) when they are stimulated. Chapter 13 (p. 525) discusses the functions of the adrenal medulla and its hormones. Figure 11.39 shows the sympathetic division.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.