Amazing Facts

The spinal cord

The spinal cord travels down from the brain
through the center of the spine. All communication between the body and
the brain travels through the spinal cord. The brain and the spinal
cord together make up the central nervous system (CNS). In a
cross-section of the spinal cord you would see that in the middle,
there is a dark, butterfly shaped region called the gray matter.
Surrounding the gray matter is the white matter.

The gray matter contains all of the nerve cell bodies. These nerves
cells include motor neurons and interneurons. Motor neurons are
involved with directing movement. Each motor neuron does this job by
sending a single long projection (axon) out into the periphery to
direct the activity of muscle fibers. Interneurons are contained
entirely within the CNS. They function by conveying messages between
other neurons. Sensory neurons are a third type of nerve cell. These
neurons have their cell bodies outside the spinal cord, but they send
processes into the spinal cord to communicate important sensory
information such as temperature, pressure, and pain.

The white matter is comprised of nerve fiber
tracts. These tracts are of two basic types. Ascending fiber tracts
travel up to the brain to convey sensory information. Descending tracts
travel down from the brain to convey motor signals. These tracts are
necessary for normal sensation and movement throughout the body. Damage
to the spinal cord at any level tends to cause loss of sensation
(anesthesia), and loss of movement (paralysis) below the level of the
injury. Oftentimes, these problems are permanent because spinal cord
neurons are unable to regenerate if they are damaged.

There are 31 pairs of spinal nerves that branch off from the spinal
cord. One pair of these nerves leaves the spine at every level from the
first cervical vertebrae to the coccyx. The spinal cord itself ends at
the level of the first or second lumbar vertebrae, but the spinal
nerves continue to travel downward so that one pair leaves at each
level of the spine. The tangle of nerves below the end of the spinal
cord is called the cauda equina or "horse's tail."

Related Tags: Brain  Human  Body  
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