Injuries to the spinal cord may be caused indirectly, as by a blow to the head or a fall, or they may be caused by forces applied directly to the cord. The consequences depend on the amount of damage the cord sustains and where damage occurs.

Normal spinal reflexes depend on two-way communication between the spinal cord and the brain. Injuring nerve pathways depresses the cord's reflex activities in sites below the injury. At the same time, sensations and muscular tone in the parts the affected fibers innervate lessen. This condition, spinal shock, may last for days or weeks, although normal reflex activity may return eventually. However, if nerve fibers are severed, some of the cord's functions are likely to be permanently lost.

Less severe injuries to the spinal cord, as from a blow to the head, whiplash in an automobile accident, or rupture of an intervertebral disk, compress or distort the cord. Pain, weakness, and muscular atrophy in the regions the damaged nerve fibers supply often accompany such injuries.

Among the more common causes of severe direct injury to the spinal cord are gunshot wounds, stabbings, and fractures or dislocations of vertebrae during vehicular accidents. Regardless of the cause, if nerve fibers in ascending tracts are cut, sensations arising from receptors below the level of the injury are lost. If descending tracts are damaged, the result is a loss of motor functions.

For example, if the right lateral corticospinal tract is severed in the neck near the first cervical vertebra, control of the voluntary muscles in the right upper and lower limbs is lost, paralyzing them (hemiplegia). Problems of the this type in fibers of the descending tracts produce upper motor neuron syndrome, characterized by spastic paralysis in which muscle tone increases, with very little atrophy of the muscles. However, uncoordinated reflex activity (hyperreflexia) usually occurs, during which the flexor and extensor muscles of affected limbs alternately spasm.

Injury to motor neurons or their fibers in the horns of the spinal cord results in lower motor neuron syndrome. It is characterized by flaccid paralysis, a total loss of muscle tone and reflex activity, and the muscles atrophy.

Copyright ©1998 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use and Privacy Policy.
McGraw-Hill Higher Education is one of the many fine businesses of The McGraw-Hill Companies.
For further information about this site contact mhhe_webmaster@mcgraw-hill.com.