Download Nervous System - Fuller Anatomy

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Spinal Cord and Nerves
Adult spinal cord is 18 inches long and 14 mm
Spinal cord does not continue in length with
the vertebrae; stops at L1 and L2
Entire spinal cord can be divided into 31
segments on the basis of the origins of the
spinal nerves
Amount of gray matter is
greatest in those areas
that deal with sensory
and motor neuron control
of the limbs.
Inferior to the lumbar the
spinal cord becomes
tapered and conical. This
region ends in branching
off of the nerves in an
area called the cauda
equina (horse’s tail).
Every spinal segment is associated with a pair of dorsal
root ganglia. The ganglia contain the cell bodies of
sensory neurons. The axons of the neurons make up the
dorsal roots. Ventral roots contain axons of motor
neurons. The sensory and motor roots are bound together
into a single spinal nerve.
Dorsal root
Ventral root
Spinal nerves are classified as mixed nerves –
contain both afferent (sensory) and efferent
(motor) fibers.
 Spinal cord continues to enlarge and elongate
until an individual is 4 years old.
 After that time vertebral column continues to
grow, but spinal cord does not. Vertebra growth
moves the intervertebral foramen and nerves
further from their original positions, thus
elongating the dorsal and ventral roots.
Spinal meninges is a series of specialized
membranes surrounding the spinal cord to
provide protection (shock absorption)
Consists of three layers:
(1) dura mater
(2) arachnoid
(3) pia mater
These layers are continuous with the cranial
meninges that surround the brain.
Pia mater
Dura mater
Between the dura mater and
the walls of the vertebral canal
lies the epidural space, a region
with loose connective tissue
and adipose
 Anesthetics are often injected
into the epidural space. The
drug should only affect spinal
nerves in the area of the
injection. Result is an epidural
block-temporary sensory loss or
motor paralysis (depending on
anesthetic) used to control pain
during childbirth.
A narrow region between the arachnoid and the
pia mater is called the subarachnoid space that is
filled with cerebrospinal fluid (CSF). The
withdrawal of the CSF occurs in a procedure called
a spinal tap. Spinal taps are done to diagnose CNS
infection, severe back pain, disc problems, and
some types of strokes.
Every segment of
the spinal cord is
attached to a pair
of spinal nerves.
A series of
connective tissue
layers surrounds
each spinal nerve
and continues
along its
Epineurium surrounds
several bundles of
Perineurium surrounds
a fascicle
surrounds individual
myelin sheaths and
A reflex is a rapid,
automatic response
to a specific stimuli.
Most reflexes occur
in the spinal cord
rather than the brain
for faster response
time. The wiring of a
single reflex is called
a reflex arc.