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1. Describe the functional anatomy of the spinal cord using the following terms: white matter, gray matter,
tracts, roots, and spinal nerves.
The spinal cord is the means by which motor and sensory information travels between the brain and
the remainder of the body. The white matter contains tracts consisting of ascending (sensory) or
motor (descending) axons. The white matter surrounds the butterfly-shaped gray matter containing
the cell bodies of neurons organized into sensory (dorsal horn) and motor (ventral horn) segments.
The spinal cord is connected to the rest of the body through roots that enter and exit the cord.
Sensory information enters the cord through dorsal roots while motor fibers exit the cord via ventral
roots. The dorsal and ventral roots fuse outside of the cord to form spinal nerves. The spinal nerves
then travel to a particular region of the body, carrying motor information to and sensory information
from that region.
2. Define the terms reflex and spinal reflex, and identify the components of a reflex arc.
A reflex is a rapid, automatic response to a change in the internal or external environment.
A reflex arc has the following five components: (i) a receptor that detects a change in the internal or
external environment (i.e., a stimulus), (ii) a sensory neuron, (iii) an information processing center
located in the gray matter of the brain or spinal cord, (iv) a motor neuron, and (v) an effector that
effects a response to the stimulus.
A spinal reflex is any reflex action in which the spinal cord is the site of information processing. In
spinal reflexes, the sensory neuron is typically unipolar in structure, with its cell body located in the
dorsal root ganglion, its dendritic process modified into the receptor, and its axonal process entering
the spinal cord via the dorsal root. Also, the cell body of the motor neuron is located in the ventral
horn of the gray matter with its axon leaving the cord via the ventral root.
3. Define the term spinal cord injury (SCI) and state its prevalence.
A spinal cord injury (SCI) is any injury to the spinal cord that results in an alteration, either
temporary or permanent, in its motor, sensory, or autonomic function. Often it is due to either a
bruise (contusion), a partial tear, or complete tear (called a transection) of the spinal cord.
About 11,000 people a year suffer a SCI. More than half of all SCIs occur among young people
between the ages of 16 and 30 years. The majority of SCI victims (82%) are male.
4. Define the terms neurological level, tetraplegia, and paraplegic.
The term neurological level (or neurological level of injury) refers to the lowest segment of the spinal
cord with normal sensory and motor function on both sides of the body. The segments at which
normal function is found often differ on sides of the body in terms of sensory and motor testing.
Tetraplegia is defined as loss of motor and sensory function at or above the C8 neurological level,
with loss of function in the arms as well as the trunk, legs, and pelvic organs.
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