Trauma and disorders of the spinal cord
While extremely flexible, the spinal cord is exceptionally sensitive to direct pressure. Localized damage to the cord or its roots results in some sort of functional loss, either paralysis, loss of motor function, or paresthesias, loss of sensory function. Severe damage results in flaccid paralysis wherein the skeletal muscles served by the cord lose their connection to the brain, rendering them unable to move, voluntarily or involuntarily. This always results in muscular atrophy. When only upper motor neurons of the primary motor cortex are damaged, spastic paralysis occurs. This means that the spinal motor neurons remain intact and the muscles, as a result, are simulated irregularly by spinal reflexes. Their movements are no longer subject to voluntary control, however, causing permanent shortening.
Transection of the spinal cord at any level results in total motor and sensory loss to regions inferior to the damage. Paraplegia is the result of damage to the thoracic section of the spinal cord; quadriplegia, the cervical section. Spinal shock occurs after traumatic spinal cord injury. It is a period of functional loss following the injury. The loss of function is identical to that of paralysis, but function usually returns within 48 hours. If not, the damage is likely permanent.
Transection of the spinal cord at any level results in total motor and sensory loss to regions inferior to the damage. Paraplegia is the result of damage to the thoracic section of the spinal cord; quadriplegia, the cervical section. Spinal shock occurs after traumatic spinal cord injury. It is a period of functional loss following the injury. The loss of function is identical to that of paralysis, but function usually returns within 48 hours. If not, the damage is likely permanent.
poliomyelitis
Poliomyelitis is caused by destruction of ventral horn motor neurons by the poliovirus. It results in paralysis and muscular atrophy, sometimes causing death if the paralysis affects the medulla oblongata.
Recently, many survivors of the polio epidemic of the 1940s and 1950s have begun exhibiting postpolio syndrome, which eventually results in progressive muscular weakness and atrophy. The cause is believed to be that they, like everyone else, are losing neurons throughout life. However, most people have enough neurons that those nearby the ones lost can be recruited to compensate. These survivors have already recruited all remaining neurons as a result of the damage from the poliovirus and have no more to call upon.
Recently, many survivors of the polio epidemic of the 1940s and 1950s have begun exhibiting postpolio syndrome, which eventually results in progressive muscular weakness and atrophy. The cause is believed to be that they, like everyone else, are losing neurons throughout life. However, most people have enough neurons that those nearby the ones lost can be recruited to compensate. These survivors have already recruited all remaining neurons as a result of the damage from the poliovirus and have no more to call upon.
Amyotrophic lateral sclerosis
Commonly known as Lou Gehrig's disease, amyotrophic lateral sclerosis is a neuromuscular condition thich involves destruction of ventral horn motor neurons and fibers of the pyramidal tracts. Eventually, the victim loses the ability to speak, swallow, and breathe. The cause is unknown, but an unusually high number of patients appear to have excess extracellular glutamate. It is believed that motor neurons are killed as a result of glutamate excitotoxicity. The only known treatment is the drug Riluzole, which prolongs the life of the patient by apparently inhibiting glutamate release.