Transcript 5 PNS and ANS

Peripheral Nervous System (PNS)
Figure 12.16a
Structure of a
Nerve
Each neuron is surrounded
by a sheath called the
endoneurium. Some axons
have an additional sheath
called myelin.
A bundle of neurons travel
together in a fascicle, and
are surrounded by
perineurium.
A bundle of fascicles is
surrounded by epineurium
Figure 12.16a
Spinal Nerves Posterior View
Figure 14.9
Cut nerves
• If a small nerve is cut, it will regenerate
because where are the cell bodies? In the
posterior root ganglion (sensory) or
anterior horn (motor).
• Since the cell body is about a meter away,
axons can regrow.
• Large nerves are harder to regrow, but
you can still stitch the ends together at the
epineurium and perineurium, and you may
get healing.
Pinched nerves
• When a nerve gets pinched (e.g. herniated
disc), it damages the nerve by interfering
with its action potential, causing
weakness, pain, or paralysis.
Disruption of Blood Supply
• When a body part “falls asleep”, the region
has become ischemic, impairing the action
potential of the nerves. Unlike the CNS,
when blood is restored to the PNS, the
nerves recover. Damage to the CNS
tends to be permanent, but damage to the
PNS tends to heal.
DAMAGE TO THE
NERVOUS SYSTEM
• If a person has a spinal cord injury in their
cervical region, they could have
quadriplegia (arms and legs paralyzed).
• If a person has a spinal cord injury in their
thoracic region, they could have
paraplegia (just legs are paralyzed).
SOME CLINICALLY IMPORTANT
PERIPHERAL NERVES:
• Note: an epidural nerve block during child birth
will numb the mother from her navel to her
knees.
• PUDENDAL NERVE: this is the nerve that can
be anesthetized during childbirth as an
alternative to an epidural (a pudendal nerve
block is also called a saddle block because the
numb areas are where you would be touching a
saddle).
• PHRENIC NERVE: allows the diaphragm to
contract. If it gets severed, the person can no
longer breathe without assistance.
SENSORY NERVES
• These come out of the spinal cord and go
to specific regions of the body. Each
region of the body is innervated by spinal
nerves.
• For example, nerve C4 innervates region
C4 of the DERMATOME.
• It’s important to know these dermatome
regions (not for this class), especially
physical therapists and nurses.
Map of Dermatomes
Figure 14.17a
SENSORY NERVES
• If a patient has a shooting pain down the
anterior shin, what nerve is pinched? L5.
• Numbness in pinky and ring finger is what
nerve? C8.
• If a workman’s comp patient comes in saying his
whole hand is numb, no other symptoms, you
know he’s lying because the nerves don’t run
that way.
• They also don’t run transversely across the
body; they are on one side or the other.
Nerve Plexus
A PLEXUS is a network of nerves that
primarily serves the limbs. There are four
major plexi: cervical, brachial, lumbar, and
sacral.
1. CERVICAL PLEXUS comes out of the
neck and are cutaneous nerves (sensory
input of the skin) of the neck and back of
the head.
Cervical
Plexus
BRACHIAL PLEXUS
2. BRACHIAL PLEXUS
• This is the major group of nerves that supply the
upper limbs. It runs through the axilla.
• If a person leans their armpits on their crutches,
they can damage this plexus and lose the use of
their arms.
• The nerves in the brachial plexus change names
as they go to different regions in the arm.
The Brachial Plexus
Figure 14.12a
Axillary
Musculocutaneus
Major Nerves
of the Upper
Extremity
Axillary Nerve
• Deltoid
Musculocutaneus Nerve
• Supplies anterior muscles of the arm
Median Nerve
• Supplies no muscles of the arm
• Supplies anterior forearm (except flexor
carpi ulnaris)
• Carpal Tunnel Syndrome
– Hand of benediction
Carpel Tunnel Syndrome
• The median nerve travels under the
transverse carpal ligament.
• The nerve is pinched in carpal tunnel
syndrome.
Carpel Tunnel Syndrome
Carpel Tunnel Syndrome
MEDIAN NERVE
• This is the nerve that gets cut when people try to
slit their wrists.
• The arteries are so small in the wrist; people
rarely die from this type of suicide attempt.
However, they live with a lot of tissue damage.
They are not able to move the thumb towards
the little finger, so it is hard to pick up small
objects. This is called “ape hand”.
Ulnar Nerve
• Supplies flexor carpi ulnaris
• “Funny Bone”
• Damage can cause claw hand; cannot
adduct or abduct fingers
Radial Nerve
• Supplies muscles on the
posterior arm and forearm
• Damage can cause wrist drop
Carpel Tunnel
Syndrome
Axillary, Radial,
Ulnar, Median Nerves
Figure 14.4
Brachial Plexus
• Damage to Brachial Plexus
– Klumpke’s paralysis (brachial plexus damaged
during birth)
– Acquired Brachial Plexus injuries
• Crutch paralysis (total upper extremity paralysis)
• Claw Hand / Ape hand
• Hand of benediction
• Wrist Drop (Waiter’s Hand)
LUMBAR PLEXUS
3. LUMBAR PLEXUS
• FEMORAL NERVE is the main nerve to
the anterior thigh.
Lumbo-Sacral Plexus
• Lumbar:
– Femoral nerve
• Sacral:
– Sciatic nerve
The Lumbar Plexus
Figure 14.15
Sacral Plexus
4. SACRAL PLEXUS are spinal nerves from L4-S5
• Some of the fibers from the lumbar plexus mix with the
sacral plexus, so these are often referred to together as
the lumbosacral plexus.
• SCIATIC NERVE is the largest branch of the sacral
plexus and the largest nerve in the body; it leaves the
pelvis through the sciatic notch.
• A short, thick muscle (Piriformis muscle) covers the
sciatic notch, and when it contracts, it can pinch the
sciatic nerve, causing a type of sciatica (sciatic nerve
irritation) known as piriformis syndrome.
• This can be alleviated by stretching exercises. However,
sciatica can also be caused if there is a herniated lumbar
disc, in which case stretching exercises make it worse.
The Sacral Plexus
Figure 14.16a, c
Obturator
Femoral
Nerves of the
Lower
Extremity
The sciatic nerve supplies
the back of the thigh, then
branches out into the
TIBIAL and FIBULAR
(peroneal) nerves, which
supply the leg and foot.
The fibular nerve
branches into superficial
and deep.
Lower Extremity Nerves
Obturator Nerve
Supplies adductor muscles
Sciatic Nerve
Supplies back of thigh, leg and foot
Femoral Nerve
Supplies anterior Thigh
Tibial Nerve
Supplies posterior leg and foot
Common Fibular Nerve
Superficial branch
Supplies lateral side of leg
Deep branch
Supplies anterior leg
Injury causes “Foot Drop”
Tibial Nerve
• Sometimes a small branch of the tibial nerve in
the foot gets pinched between the metatarsal
heads, and the irritation causes nerve swelling
and pain.
• It is called a neuroma (“nerve tumor”) and
manifests as pain in the ball of the foot, made
worse with high heels.
• An injury to the fibular nerve may result in “foot
drop”, where the foot cannot be dorsiflexed.
AUTONOMIC NERVOUS SYSTEM
• We don’t have voluntary control over these
nerves.
• They are involved digestion, blood flow,
urination, defecation, glandular secretion.
• Therefore, the ANS supplies the glands,
smooth muscle, and cardiac muscle, but
NOT the skeletal muscle.
• For this reason, the ANS is also called the
general visceral motor system.
Sympathetic Division of the ANS
Figure 15.7
ANS
• All of the neurons of the ANS are motor neurons
(there are no sensory neurons in the ANS).
• The ANS differs from the CNS reflex arc
because the ANS has two lower motor neurons
in the periphery (the cell body of one is in the
spinal cord and the cell body of the other is in
the periphery), whereas the CNS has one lower
motor neuron, and its cell body is within the
spinal cord, not in the periphery.
ANS
• The ANS neuron comes from the spinal cord
and synapses on the cell body of another
neuron, which then synapses on the target
(gland, blood vessel, etc).
Ganglia
• The area where the two neurons come
together is the AUTONOMIC GANGLIA.
• The first neuron is the PRE-GANGLIONIC
NEURON.
• The second neuron is the POSTGANGLIONIC NEURON.
• Some of these ganglia (those in the
sympathetic division of the ANS) are lined up
along the vertebral column, called a structure
called the sympathetic trunk ganglia.
ANS
• The ANS motor unit is characterized by
having more than one lower motor neuron,
the axons may be myelinated or
unmyelinated, conduction is slow, and the
axons are thin.
• The ANS has two divisions:
sympathetic and parasympathetic.
ANS has TWO lower motor neurons
Preganglionic
neuron
CNS has just one lower
motor neuron
Post-ganglionic
neuron
Ganglion (where the cell
bodies of the postganglionic neurons are)
SYMPATHETIC DIVISION
• ↑heart rate and blood pressure,
• ↑metabolic activity (increased blood
glucose),
• decreased peristalsis (decreased food
digestion)
• dilation of bronchioles
• control of blood flow to the skin
• sweating
Sympathetic Division
• E.g. when running, ↑heart rate =
sympathetic.
• When hot  sweat = sympathetic.
• The term “Fight or Flight” is inaccurate; it
refers to the ↑ heart rate, etc, but the
sympathetic division is also active when
relaxing on a nice beach with a cool drink
on a hot day, because whenever you’re
sweating, that’s the sympathetic division.
ANATOMY OF THE
SYMPATHETIC DIVISION
• The sympathetic neurons exit the spinal cord
at the thorax and lumbar regions.
• The axons of most pre-ganglionic neurons in the
sympathetic division are fairly short, and they
synapse quickly on a ganglia.
• All these ganglia together are the
SYMPATHETIC TRUNK (CHAIN) GANGLIA.
• Therefore, the postganglionic cell bodies of
the sympathetic nervous system are in the
chain ganglia.
• There are also nerves that connect the ganglia
to each other.
Sympathetic Trunk Ganglia
Figure 15.8
Sympathetic Division
In Sympathetic division,
preganglionic axons are
SHORT because they
terminate in ganglia that
are close to the spinal
cord
That means the postganglionic axons are
LONG, because they have
to reach all the way to the
target muscle.
Sympathetic Division
• The axons of POST-GANGLIONIC NERVES are
very long, and go to the target organs.
• Some pre-ganglionic neurons bypass the
sympathetic chain ganglia and go directly to the
abdomen.
• They create a group of ganglia in the abdomen
called the SOLAR PLEXUS (“sun”). When you
get punched in the abdomen, you are punched
in the solar plexus, and get the wind knocked out
of you.
PARASYMPATHETIC DIVISION
• Unlike the sympathetic division, the axons of the
preganglionic neurons of the parasympathetic
division are long, and the axons of the
postganglionic neurons are short.
• The nerve cell bodies (peripheral ganglia) of
the parasympathetic division are closer to
the organs being innervated than in the
sympathetic division.
• In fact, the cell bodies are either next to or
inside of the target organs. Therefore, they
have short post-ganglionic fibers.
Parasympathetic Division
In the Parasympathetic
division, preganglionic
axons are LONG
because they terminate
in ganglia that are close
to the target organ
That means the postganglionic axons are
SHORT
PARASYMPATHETIC DIVISION
• Involved in vegetative activities, such as
digestion, urination, defecation
• Has postganglionic cell bodies in terminal
ganglia, located either near or within target
organs
• Has both preganglionic and postganglionic
neurons that secrete acetylcholine
• Has preganglionic cell bodies located in the
cranial and sacral areas.
Parasympathetic Division
• The function of this division is often antagonistic
(opposite) of the sympathetic, but actually, they
work together.
• The parasympathetic division inhibits cardiac
contraction, so there is: ↓heart rate, constricts
bronchioles, activates digestive system, and
causes salivation, urination, and defecation.
• When you are lounging on the beach, the heart
rate decreases (parasympathetic), but the sweat
increases (sympathetic).
Vagus Nerve
• The parasympathetic neurons come out of
either the brain or the sacral region of the
spinal cord.
• The majority of the parasympathetic
outflow from the head is by the vagus
nerve.
Vasovagal Syncope (Fainting)
• The most common type of fainting.
• After a stressful trigger, the parasympathetic nervous
system is enhanced by the Vagus nerve.
• The heart rate speeds up, then suddenly drops.
• Then the blood pressure drops.
• Unconsciousness results.
• Treatment: elevate the legs above the heart for a few
minutes, and make sure the airway remains open.
• A cold, wet cloth on the forehead and back of the neck
may make the person feel better as they recover.
Path of the Vagus Nerve
Figure 15.6
Reynaud's Phenomenon
• Autonomic nervous system is
hyperactive in the ANS
neurons that innervate the
walls of blood vessels.
• It causes spasms of peripheral
blood vessels, cuts off some
blood supply, and causes the
fingers and toes to be white or
blue.
• Emotional stress and being
cold tend to trigger the
discoloration.
VISCERAL (“organ”) SENSES
• A visceral nerve innervates involuntary effectors
(smooth muscles in organs).
• A somatic motor nerve innervates voluntary
effectors (skeletal muscle).
– (don’t confuse this with a somatic sensory nerve for
the sense of touch; sensory nerves are not part of the
ANS)
VISCERAL (“organ”) SENSES
• Internal organs also have sensory nerves that
tell you when you have eaten enough or your
bladder is full. These are not part of the ANS
because they are sensory.
• Not all organs have sensory nerves, for
instance, you can’t feel when you have high
blood pressure.
• You can also have visceral reflexes, which
trigger the parasympathetic system to contract
the bladder when full, etc.
• Reflexes are hard to localize.
Referred Pain
• Pain in an organ may not be where the organ is.
• Heart pain usually manifests in the left side of
chest, the left shoulder, arm, but not the heart.
• This is REFERRED PAIN.
• Pain in the lungs usually shows up as neck pain.
• These areas of referred pain are important to
know, but not for this class.
A Map of Referred Pain
Figure 15.15
Caffeine
• With frequent use, tolerance to many of
the effects of caffeine will develop. At
doses of 600 milligrams (about six cups of
coffee) or more daily, caffeine can cause
nervousness, sweating, tenseness, upset
stomach, anxiety, and insomnia. It can
also prevent clear thinking and increase
the side effects of certain medications.
This level of caffeine intake represents a
significant health risk.
Caffeine
• Caffeine can be mildly addictive. Even
when moderate amounts of caffeine are
withdrawn for 18 to 24 hours, one may feel
symptoms such as headache, fatigue,
irritability, depression, and poor
concentration. The symptoms peak within
24 to 48 hours and progressively decrease
over the course of a week. To minimize
withdrawal symptoms, experts recommend
reducing caffeine intake gradually.
Caffeine
• At levels over 200 milligrams per day, caffeine
may delay conception and doubles the risk of
miscarriages and low birth weight babies.
• Caffeine and tannin in tea decreases iron and
protein absorption, and is especially dangerous
during pregnancy.
• Caffeine taken during pregnancy is thought to
increase the probability of a child contracting
diabetes.
• Because children have developing nervous
systems, it is important to moderate their
caffeine consumption.
Caffeine
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Expresso: 502 mg
Jolt Energy: 280 mg
Coffee: 85 mg
Red Bull: 80 mg
Mountain Dew: 55 mg
Green tea: 50 mg
Tea: 47 mg
Coke: 37 mg
Dark Chocolate (1.5 oz): 20 mg
Milk Chocolate (1.5 oz): 9 mg
Hot Chocolate: 5 mg
Root Beer, Ginger ale, Lemon-Lime: 0 mg
Symptoms of Excess Caffeine
• nervousness
• anxiety
• irritability
• agitation
• tremors
• insomnia
• depression
headache
upset stomach
GI irritation
heartburn
diarrhea
fatigue
dizziness
increased heart rate
irregular heartbeat
elevated BP
increased cholesterol
nutritional deficiencies
poor concentration
bed wetting
Caffeine Withdrawal Symptoms
•
•
•
•
•
•
•
headache
craving
irritability
insomnia
fatigue
depression
apathy
constipation
runny nose
anxiety
nausea
nervousness
vomiting
shakiness
cramps
dizziness
ears ringing
drowsiness
hot and cold
inability to concentrate
The Autonomic Nervous System
Def: The ANS consists of all visceral motor
neurons innervating smooth muscle, cardiac
muscle and glands.
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Sympathetic and Parasympathetic
Divisions of the ANS
• How they are similar:
– Both divisions are part of
the ANS
– Both have effects on
smooth muscle, cardiac
muscle and glands
• How they differ:
– Stimulation of effectors by
each system vary from one
body system to another.
Effects may be stimulatory
or inhibitory.
– Location
– Length of pre and
postganglionic fiber
– Neurotransmitters used
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Comparison of ANS and Somatic Motor
Pathways
• Somatics
– Single neuron from spinal
cord to effector
– One neuron innervates the
effector cell
– NTS is acetylcholine (ACh)
• Autonomics
– Two neurons relay
(ganglion) to effector
– Dual innervation of
effectors
– NTS at ganglia (ACh); NTS
at effector can be ACh or
norepinephrine
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Location and neurotransmitters
used by Sympathetic/Parasymp
adrenergic receptors
sympathetic
preganglionic neuron
postganglionic neuron
parasympathetic
nicotinic receptors
muscarinic receptors
Characteristics of Sympathetic and
Parasympathetic Function
•
Post-ganglionic sympathetic nerves release
norepinephrine at their nerve endings
– these nerves are called adrenergic nerves
•
Pre and post-ganglionic parasympathetic
nerves release acetylcholine at their nerve
endings (Nitric oxide- corpora cavernosa)
– these nerves are called cholinergic nerves
•
EXCEPTION FOR SYMPATHETIC:
– Cholinergic: mACH; used in body wall.
– Vasodilation of vessels in brain and
skeletal muscle
– Piloerector muscles
– Sweat glands
– Nitric oxide: vasodilation of vessels in
brain, skeletal muscle
Sympathetic
Nervous System
“Thoracolumbar”
When active?
Length of pre and
postganglionic
nerve?
Location of cell
bodies of
preganglionic nerve?
Location of cell
bodies of
postganglionic
nerve?
Neurotransmitters
released?
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Adrenal medulla

Figure 60-1;
Guyton & Hall
Parasympathetic
Nervous System
“cranio-sacral”
Parasympathetic nerves originate
from cranial nerves III, VII, IX, and X
and the sacral spinal cord.
occulomotor nerve - fibers to
the pupillary sphincters and
ciliary muscle
facial nerve - fibers to lacrimal
and submandibular gland
glossopharyngeal nerve - fibers
to parotid gland
vagus nerve - motor inputs to
visceral organs
sacral segments - fibers to
descending colon, rectum,
bladder and genitalia
Figure 60-3;
Guyton & Hall
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Effects of the ANS on the Organs
• eye
– sympathetic --pupillary dilation
(alpha 1 receptor)
– parasympathetic--pupillary
constriction and
accommodation (focusing) of
the lens (mACh receptor)
• glands of the body
– parasympathetic stimulate the
nasal, lacrimal, salivary, and
G.I. glands (mACh receptor)
– sympathetic stimulates the
sweat glands (mACh receptor)
Effect of the Autonomic Nervous
System on the Organs
• G.I. tract
– parasympathetic stimulates overall
activity including G.I. smooth muscle
– sympathetic has very little effect
• heart
– sympathetic increases the rate and
contractility
– parasympathetic decreases heart rate
• blood vessels
– sympathetic causes vasoconstriction.
Reduced sympathetic response accounts
for most vasodilation.
– parasympathetic causes some
vasodilation (e.g., penis)
Sympathetic and Parasympathetic
“Tone”
• the basal rate of activity
of each system
• this background activity
allows for an increase or
decrease in activity by a
single system
– sympathetic tone
normally causes about a
50 % vasoconstriction
• increasing or decreasing
“tone” can change vessel
diameter
– parasympathetic tone
provides background
G.I. activity
adrenergic or sympathomimetic
drugs act like norepinephrine
• these drugs have an effect which is much more prolonged
than that of either norepinephrine
– phenylephrine stimulates alpha receptors
– isoproterenol stimulates both beta1 and beta2 receptors
– albuterol stimulates only beta2 receptors
• some drugs act indirectly by increasing the release of
norepi from its storage terminals
– ephedrine, amphetamine, pseudoephedrine,
Pharmacology of the Sympathetic
Nervous System
• drugs that block the
effect of
norepinephrine
• alpha blockers
– phentolamine
– Cheap Viagra!
• beta blockers
– beta1 and 2 propranolol
Pharmacology of the
Parasympathetic Nervous System
• parasympathomimetic drugs
– muscarine
– pilocarpine
• activates muscarinic
receptors, cause profuse
sweating (why if sweat
glands are controlled by
sympathetic system?)
• cholinesterase inhibitors
– neostigmine, potentiates the
effect of acetylcholine
• antimuscarinic drugs
– atropine blocks the effect of
acetylcholine on effector cells