The spinal cord is about 18 inches long and
extends from the base of the brain, down the middle of the back, to
about the waist. The nerves that lie within the spinal cord are upper
motor neurons (UMNs) and their function is to carry the messages back
and forth from the brain to the spinal nerves along the spinal tract.
The spinal nerves that branch out from the spinal cord to the other
parts of the body are called lower motor neurons (LMNs). These spinal
nerves exit and enter at each vertebral level and communicate with
specific areas of the body. The sensory portions of the LMN carry
messages about sensation from the skin and other body parts and organs
to the brain. The motor portions of the LMN send messages from the
brain to the various body parts to initiate actions such as muscle
movement.
The spinal cord is the major bundle of nerves that
carry nerve impulses to and from the brain to the rest of the body. The
brain and the spinal cord constitute the Central Nervous System. Motor
and sensory nerves outside the central nervous system constitute the
Peripheral Nervous System, and another diffuse system of nerves that
control involuntary functions such as blood pressure and temperature
regulation are the Sympathetic and Parasympathetic Nervous Systems.
The
spinal cord is surrounded by rings of bone called vertebra. These bones
constitute the spinal column (back bones). In general, the higher in
the spinal column the injury occurs, the more dysfunction a person will
experience. The vertebra are named according to their location. The
eight vertebra in the neck are called the Cervical Vertebra. The top
vertebra is called C-1, the next is C-2, etc. Cervical SCI's usually
cause loss of function in the arms and legs, resulting in quadriplegia.
The 12 vertebra in the chest are called the Thoracic Vertebra. The
first thoracic vertebra, T-1, is the vertebra where the top rib
attaches.
Injuries in the thoracic region usually affect the
chest and the legs and result in paraplegia. The vertebra in the lower
back between the thoracic vertebra, where the ribs attach, and the
pelvis (hip bone), are the Lumbar Vertebra. The sacral vertebra run
from the Pelvis to the end of the spinal column. Injuries to the five
Lumbar vertebra (L-1 thru L-5) and similarly to the five Sacral
Vertebra (S-1 thru S-5) generally result in some loss of functioning in
the hips and legs.
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