women who have had one child with spina bifida
are more likely to have others. Researchers are
not certain whether the connection is genetic or
environmental.
See also BIRTH DEFECTS; NEURAL TUBE DEFECTS; PRE-
NATAL CARE.
spinal cord The largest NERVE in the body,
extending from the base of the BRAIN (medulla
oblongata) through the spinal canal to the second
lumbar vertebra. The average adult spinal cord is
16 to 20 inches long and about the thickness of a
man’s thumb. The outer structure of the spinal
cord is white matter (myelinated neuronal axons);
the inner structure is gray matter (NEURONcell
bodies). The inner gray matter is roughly the
shape of an H, with the horns extending to the
roots of the 31 pairs of SPINAL NERVESthat branch
from the spinal cord.
The spinal cord is the primary neurologic con-
duit between the body and the brain. It transmits
motor nerve impulses from the brain to the body
and sensory nerve impulses from the body to the
brain. The spinal cord also has rudimentary filter-
ing and control functions, responding to certain
kinds of nerve impulses, and serves as the center
for reflexes related to urination, defecation, and
MUSCLEstretch (essential for movement and bal-
ance).
The spinal column, a sequence of joined verte-
brae, encloses and protects the spinal cord. CARTI-
LAGEcushions between each vertebra (vertebral
disks) allow the spine to flex and twist without
jeopardizing the spinal cord. Significant trauma,
such as may occur in an automobile accident, can
compress, bruise, or sever the spinal cord. Such
injuries cause paralysis. A severed spinal cord can-
not regenerate, though sometimes partial to full
function returns with release of the source of
compression or after HEALINGof a bruise. Tumors
may also compress the spinal cord.
For further discussion of the spinal cord within
the context of the structures and functions of the
nervous system, please see the overview section
“The Nervous System.”
See also HERNIATED NUCLEUS PULPOSUS; MOTOR
VEHICLE ACCIDENTS; NEUROFIBROMATOSIS; REFLEX;
SPINAL CORD INJURY.
spinal cord injury Traumatic damage to the
SPINAL CORD, usually the result of a blow to the
spine or sudden, forceful twisting. MOTOR VEHICLE
ACCIDENTS account for 40 percent and VIOLENCE
(gunshot and knife wounds) accounts for 25 per-
cent of spinal cord injuries in the United States.
Other common causes are diving into shallow
water, sports-related injuries, and significant falls.
More than 80 percent of those who experience
spinal cord injuries are men, more than half of
whom are under age 30.SPINAL CORDinjury is a medical emer-
gency that requires immediate treat-
ment at a neurologic trauma center. It is
critical that only properly trained med-
ical personnel attempt to move some-
one who may have suffered a spinal
cord injury.Such injuries typically cause the vertebrae to
compress the spinal cord, damaging the long
axons that make up the spinal cord’s white matter.
The axons are the fibers that extend from neurons
in the BRAINand brainstem. This type of injury,
which neurologists classify as incomplete, permits
some NERVEimpulses to travel the spinal cord and
is sometimes recoverable. Much less commonly,
trauma partially or completely severs the spinal
cord. A complete spinal cord injury exists when
no nerve impulses can travel through or around
the point of trauma. Circumstances that increase
the damage include bleeding, which can increase
pressure and/or directly damage neurons, and a
surge of neurotransmitters, notably glutamate, at
the site of the injury, which overwhelms and kills
neurons.Symptoms and Diagnostic Path
The primary symptom of spinal cord injury is
immediate PARALYSIS below the point of trauma.
When the injury is high on the spinal cord, above
the lumbar vertebrae, the paralysis may affect the
DIAPHRAGMand muscles of the chest, preventing
the mechanics of BREATHING from taking place.
Injury at the cervical level is most severe; injury at
the C1 or C2 level is usually not survivable
because this is the level of neurologic functionsspinal cord injury 283