Peripheral
Nervous
System
PNS consists of nerves that branch out from
the CNS and connect to other body parts.
•
Somatic (outer; voluntary) nerves that connect CNS to skin
and skeletal muscles for
conscious movement and
sensory input.
•
Autonomic (visceral; involuntary)
– connect CNS to visceral
organs (heart, stomach,
intestines, other glands) for
unconscious activities.
Receptors
• External receptors (exteroceptors)
– Sensitive to stimuli outside the body. Found at or
near body surface (e.g. touch, pressure, pain).
• Internal receptors (interoceptors)
– Receive stimuli arising from internal viscera (e.g. GI
tract, bladder, lungs).
• Proprioreceptors
– Measures the degree of stretch of locomotor organs,
sending positional information to the CNS.
Components
• Nerves – most are mixed
nerves with both sensory
and motor fibers.
– Cranial nerves (12 pair)
attached to brain
– Spinal nerves (31 pair)
attached to the spinal
cord.
• Ganglia
– Aggregation of nerve cell
bodies
Cranial Nerves
•
•
•
12 pair, numbered I-XII from rostral (superior) to caudal (inferior).
First 2 from forebrain, the rest from the brain stem.
All serve the neck and head, except the vagus (thoracic and abdomen).
Cranial nerves S=sensor M=motor B=both(mixed)
I
II
III
IV
V
Name
Olfactory
Optic
Oculomotor
Trochlear
Trigeminal
S,M, or B
S
S
M
M
B
VI Abducent
VII Facial
M
B
VIII Vestibulocochlear
IX Glossopharyngeal
S
B
X
Vagus
B
XI
Accessory
M
XII Hypoglossal
M
Function
smell
vision
eye muscles
eye muscles
S- face & scalp
M- muscles of mastication
eye muscles
S- tongue & taste
M- facial muscles
hearing & equilibrium
S- tongue & taste
General sensation of pharynx
M- pharyngeal muscles(swallowing)
S- visceral sensation
M- visceral movement
swallowing, head & shoulder
movement
tongue- speech & swallowing
Extra credit – 5 pts., you come up with an original saying. If you and a friend
work on it together and it is too similar……..
I
II
III
IV
V
Name
Olfactory
Optic
Oculomotor
Trochlear
Trigeminal
On
Old
Olympos’
Towering
Top
VI Abducent
VII Facial
A
Fin
VIII Vestibulocochlear
IX Glossopharyngeal
And (V?)
German
X
Vagus
Viewed
XI
Accessory
A
XII Hypoglossal
Hop
S=sensor
M=motor
B=both(mixed)
Spinal Nerves
• 31 pairs, each exits spinal
cord between vertebrae
(except C1 which is above),
inferior to vertebra of same
number.
• Mixed nerves (sensory and
motor) that provide two way
communications between
spinal cord and arms, legs and
trunk.
Spinal Nerves
• Mixed – motor and sensory
– Afferent – carry sensory
info to spinal cord (CNS)
from receptors.
– Efferent – carry motor info
out to effector organs
• Somatic – skeletal muscles
• ANS – smooth muscle, glands
Roots and Branches
•
Each nerve emerges by 2 short roots in spinal column.
– Dorsal (sensory) – note dorsal root ganglion contains cell bodies of
sensory neurons which conduct impulses inward from peripheral body.
– Ventral (motor) – consists of axons from motor neurons whose cell
bodies are located in gray matter of spinal cord.
•
Roots unite to form spinal nerve proper which passes through intervertebral
formamen and the splits into branches.
• Spinal nerve splits just lateral to intervertebral foramen.
• Dorsal ramus (posterior branch); nerve turns posteriorly and innervates
muscles and skin of back.
• Ventral ramus (anterior branch); main portion continues anteriorly to
supply muscles and skin on front and sides of trunk and limbs.
•
Rami communicantes (communicating rami of ANS)
– Serves sympathetic motor nerves.
•
Rami communicantes consist of preganglionic, postganglionic and
sensory axons.
The ANS always displays two neurons in the motor pathway from CNS to the
effector organ.
- This contrasts with the situation in the somatic-efferent system where
there is one neuron in the path from CNS to a skeletal muscle effector.
The two ANS neurons are designated the pre- and post-ganglionic neurons.
Nervous System
Afferent Division
(sensory division)
Efferent Division
(motor division)
Autonomic
Sympathetic
“Stress”
Somatic
Parasympathetic
“Calm”
1. Preganglionic (pre-g) neurons and their axons (fibers)
- Cell body located in the CNS, originates in lateral horn.
- its axon may reach most, or only part, of the distance to target organ it
projects to through ventral root,
- and synapses on, the postganglionic neuron in chain ganglia
2. Postganglionic (post-g) neurons and fibers
- the cell body is located in an autonomic ganglion (motor ganglion)
- its axon may be relatively short, or long
- it projects to, and synapses on, a visceral effector organ
•
Rami communicantes (communicating rami of ANS)
– Rami communicantes consist of preganglionic, postganglionic and sensory
axons.
•
White rami communicantes consist of the many myelinated pre-g fibers
leaving their spinal nerve. Gray rami communicantes consists of many
non-myelinated post-g fibers returning to each mixed spinal nerve.
Reflex Arc
Five essential components: 1) receptor, 2) afferent neuron, 3) interneuron,
4) efferent neuron and 5) effector organ.
Plexuses
• Ventral rami of
spinal nerves
combine to form
complex networks
called plexuses.
Plexuses
• Each terminal branch
of plexus contains
fibers from several
different spinal nerves
• Each muscle in a limb
receives nerve fibers
from more than one
spinal nerve.
Innervation of Skin
• Dermatomes - each pair of spinal nerves supplies a
particular area of body skin.
• Dermatome map help localize sites of injury to dorsal
roots (sensory) of the spinal cord.
Autonomic Nervous System
And Visceral Sensory Neurons
ANS consists of motor neurons that serve:
• Cardiac muscle
• Smooth muscle
– Viscera – respiratory, digestive, excretory and genital organs
– Blood vessels
• Glands
– Adrenal gland
Comparison of Somatic Motor Nerves and ANS Motor Nerves
Somatic
vs.
ANS
1. Voluntary control
Involuntary control
2. Innervates skeletal muscle
Innervates cardiac and
smooth muscle, and glands
2 neurons (pre and post
synaptic)
½ myelinated:
presynaptic thinly myelinated
post synaptic nonmyelinated
3. One neuron (CNS to skeletal muscle)
4. Myelinated
Sympathetic vs. Parasympathetic
• The 2 ANS divisions generally act as antagonists,
one will activate, the other inhibit most organs.
• Sympathetic (norepinephrine) speeds up heart.
• Parasympathetic (acetylcholine) will slow it down.
• Both systems are usually operating with one
exerting more influence depending upon the
situation.
Parasympathetic Division
• Preserves normal resting functions. Protects and
preserves resources. Most active under ordinary,
restful (calm) conditions.
• Postganglionic membrane secretes acetylcholine.
• Terminal ganglia are located near visceral organ (not in
chain ganglia), so postganglionic fibers are short.
Craniosacral Out Flow
• Cranial Parasympathetic Outflow
– Innervates head, neck , thorax, most of
abdomen
• Sacral Parasympathetic Outflow
– Innervates abdomen (distal colon) and
pelvic organs (bladder, reproductive
organs)
Sympathetic Division
• More extensive than parasympathetic system. Supplies visceral
organs and superficial ‘visceral’ structures (sweat glands, arrector
pili muscles, smooth muscles of blood vessels).
• Stress division.
• Postganglionic fibers secrete norepinephrine.
• Terminal ganglia near spinal cord, post-g long.
• Axons branch profusely.
Thoracolumbar
Outflow
• Spinal nerve outflow
• Sympathetic trunk
(sympathetic chain),
formed by paired ganglia
• Preganglionic cell bodies
lie in lateral horn of
spinal gray matter.
Other ganglia are nearer
to the effector organ.