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Chapter 7 – Part 5
The Nervous System
Spinal Cord
 Extends from the medulla
oblongata to the region of
T12
 Below T12 is the cauda
equina (a collection of
spinal nerves)
 Enlargements occur in the
cervical and lumbar
regions
 Where the nerves serving
the upper and lower limbs
arise and leave the cord
Spinal Cord
 Provides a two-way
conduction pathway to
and from the brain.
 It is a major reflex
center (the spinal
reflexes are completed
as this level)
 Cushioned and
protected by meninges
Spinal Cord
 There is no possibility of
damaging the cord
beyond L3
 The meningeal sac
inferior to that point
provides a nearly ideal
spot for removing CSF
for testing.
 31 pairs of spinal nerves
Spinal Cord Anatomy
 Exterior white mater
 Composed of myelinated conduction
tracts
Spinal Cord Anatomy
 Internal gray matter
 Composed mostly of cell bodies
 Looks like a butterfly or the letter H
Spinal Cord Anatomy
• Interior Gray Matter
• Posterior (dorsal) horns – two posterior
projections
• Anterior (ventral) horns – two anterior
projections
Spinal Cord Anatomy
• Central canal
• Contains cerebrospinal fluid
• Surrounded by gray matter
Spinal Cord Anatomy
 Nerves leave at the level of each
vertebrae
 The dorsal and ventral roots fuse to
form the spinal nerves
 Dorsal root
 The fibers of sensory neurons enter the cord
here
 Ventral root
 The axons of motor neurons exit the spinal
cord here
Peripheral Nervous System
 Nerve = bundle of neuron fibers found
outside the CNS
 Neuron fibers are bundled by
connective tissue
Structure of a Nerve
 Endoneurium
surrounds each fiber
 Groups of fibers are
bound into fascicles
by perineurium
 Fascicles are bound
together by
epineurium
Cranial Nerves
 12 pairs of
nerves that
mostly serve
the head and
neck
 Numbered in
order, front to
back
 Most are
mixed nerves,
but three are
sensory only
Spinal Nerves
 There is a pair of spinal nerves at the
level of each vertebrae for a total of 31
pairs
 Spinal nerves are formed by the
combination of the ventral and dorsal
roots of the spinal cord
 Spinal nerves are named for the region
from which they arise
Spinal Nerves
Anatomy of Spinal Nerves
 Spinal nerves divide soon
after leaving the spinal
cord (each spinal nerve is
only about ½ inch long)
 The rami, contain both
motor and sensory fibers.
1. Dorsal rami – serve
the skin and muscles of
the posterior trunk
2. Ventral rami – serve
the limbs, the
intercostal muscles,
and the skin and
muscles of the anterior
and lateral trunk
Examples of Nerve Distribution
Figure 7.23
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.66
Autonomic Nervous System
 The involuntary branch of the nervous
system
 Consists of only motor nerves
 Divided into two divisions
1. Sympathetic division
2. Parasympathetic division
Autonomic Nervous System
 Body organs served
by the autonomic
nervous system
receive fibers from
both divisions.
 When both divisions
serve the same
organ, they cause
antagonistic effects.
Autonomic Functioning
 Sympathetic – “fight-or-flight”
 Response to unusual stimulus
 Takes over to increase activities
 Increases heart rate, blood pressure, blood
glucose levels, dilates the bronchioles of the
lungs, and dilates the pupils
 Remember as the “E” division = exercise,
excitement, emergency, and embarrassment
Autonomic Functioning
 Sympathetic – “fight-or-flight”
 The effects of sympathetic nervous system
activation continue for several minutes
until its hormones are
destroyed by the liver.
 Helps explain why we
need time to “calm
down” after an
extremely stressful
situation.
Autonomic Functioning
 Parasympathetic –
housekeeping activites
 “Resting and digesting” system
 Chiefly concerned with promoting normal
digestion and elimination of feces and urine
and with conserving body energy
 Heart rate, blood pressure, and respiratory rates
are at low normal levels; pupils are constricted;
skin is warm; digestive tract is actively digesting
food
 Remember as the “D” division - digestion,
defecation, and diuresis (urination)