Nervous System Part 6
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Transcript Nervous System Part 6
Chapter 7 – Part 6
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 Matter
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
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)
Anatomy of Spinal Nerves
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
Autonomic Nervous System
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)