The spinal (or vertebral) column is composed of 33 bony
rings or vertebrae, named for the region of the spine in which they are located
and numbered cephalad to caudal: 7 cervical vertebrae (C1-7), 12 thoracic
vertebrae (T1-12), 5 lumbar vertebrae (L1-5), 5 vertebrae fused as the sacrum
(S1-5), and 4 coccygeal vertebrae.
The first cervical vertebra, C1, articulates with the
skull. The last vertebrae, in the sacrum, form the posterior wall of the
pelvis. Between the vertebrae are cartilaginous disks for cushioning. Along
the length of the spinal column are ligaments for support. Openings between
each bony segment, called foramina, allow the nerve roots to exit the spinal
The spinal cord extends from the base of the brain through
the spinal canal to the second lumbar vertebra (L2), with nerves exiting
the cord between each pair of vertebrae and continuing through the spinal
canal as the cauda equina. The spinal cord segments are numbered for the
level at which the nerve root exits the spinal column.
During an injury, the spinal column and the spinal cord
can be injured anywhere along their length. The majority of the damage to
the spinal cord occurs at the time of injury, but further damage can be caused
by improper handling of the unstable spine and by the disruption of the blood
supply, which can cause hypoxia and necrosis.
Immediately following SCI, spinal shock occurs in the
portion of the spinal cord that is injured and results in a complete loss
of all motor, sensory, reflex, and autonomic function below the level of
the injury. This loss is manifested in loss of bowel and bladder tone and
peripheral vascular tone, which result in bladder distention, paralytic ileus,
flaccid paralysis, and hypotension.
After a period that varies from hours to months, but
which usually lasts for 1 to 6 weeks, the spinal neurons gradually regain
their excitability and the period of spinal shock ends. The earliest indication
is the return of the perianal reflexes. The bulbocavernous reflex has returned
if a slight muscle contraction follows squeezing of the glans penis or pulling
the indwelling catheter. The anal flex has returned if there a puckering
of the anal sphincter following a digital examination of the rectum, insertion
of a rectal thermometer, or a scratching of the skin around the anal area.
The flaccid paralysis during spinal shock is replaced by spastic paralysis
The degree of neuron excitability that returns can be
greater than before the injury. Depending on the degree of spinal shock and
the completeness of the injury, either:
Transmission of impulses will resume, along with motor, sensory, reflex,
and autonomic activity below the level of the injury, or,
The isolated cord segment will develop its own reflex activity: minimal reflex
activity, flexor spasm activity, alternating flexor and extensor spasm
activities, and predominent extensor spasm activity
Spinal shock recovery can, therefore, be accompanied by complications such
as autonomic hyperreflexia, and
and autonomic dysfunctions.
Neurogenic shock is the temporary loss or disruption
of autonomic nervous system innervation below the level of injury, which
can cause orthostatic hypotension, bradycardia, lower than normal body
temperature, and loss of the ability to perspire. Orthostatic hypotension
is the rapid drop in blood pressure when an erect position is assumed, due
to inadequate blood supply to the brain, which can result in brain damage
or death. The systolic pressure can drop as low as 40 mm Hg, the diastolic
pressure can decrease to 0 mm Hg, and pooling of blood in the abdomen and
lower extremities can occur. Orthostatic hypotension is commonly seen in
patients with lesions above T7, and can result from even a slight raising
of the head of the bed for a patient with tetraplegia.