Autonomic nervous system

Powerpoint presentation on Autonomic nervous system.

2. The Autonomic
Nervous System
Visceral sensory
Visceral motor
&

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Autonomic nervous system
The autonomic nervous system is the
subdivision of the peripheral nervous
system that regulates body activities that
are generally not under conscious control
Visceral motor innervates non-skeletal
(non-somatic) muscles
Visceral sensory will be covered later

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ANS is the subdivision of the peripheral nervous
system that regulates body activities that are
generally not under conscious control
Visceral motor innervates non-skeletal (non-
somatic) muscles
Composed of a special group of neurons serving:
Cardiac muscle (the heart)
Smooth muscle (walls of viscera and blood vessels)
Internal organs
Skin
To repeat…

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Basic anatomical difference between the motor
pathways of the voluntary somatic nervous
system (to skeletal muscles) and those of the
autonomic nervous system
Somatic division:
Cell bodies of motor neurons reside in CNS (brain or
spinal cord)
Their axons (sheathed in spinal nerves) extend all the
way to their skeletal muscles
Autonomic system: chains of two motor neurons
1
st
= preganglionic neuron (in brain or cord)
2
nd
= gangionic neuron (cell body in ganglion outside
CNS)
Slower because lightly or unmyelinated
(see next diagram)

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Axon of 1
st
(preganglionic) neuron leaves
CNS to synapse with the 2
nd
(ganglionic)
neuron
Axon of 2
nd
(ganglionic) neuron extends to
the organ it serves
Diagram contrasts somatic (lower) and autonomic:
autonomic
somatic
Note: the autonomic ganglion is motor
this dorsal
root ganglion
is sensory

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Divisions of the autonomic nervous system
(visceral motor part of it)
Parasympathetic
division
Sympathetic division

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Divisions of the autonomic nervous system
Parasympathetic division
Sympathetic division
Serve most of the same organs but
cause opposing or antagonistic effects
Parasympathetic: routine maintenance
“rest &digest”
Sympathetic: mobilization & increased metabolism
“fight, flight or fright” or “fight, flight or
freeze”

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Where they come from
Parasympathetic:
craniosacral
Sympathetic:
thoracolumbar

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Parasympathetic nervous system
“rest & digest”
Also called the craniosacral system
because all its preganglionic neurons are
in the brain stem or sacral levels of the
spinal cord
Cranial nerves III,VII, IX and X
In lateral horn of gray matter from S2-S4
Only innervate internal organs (not skin)
Acetylcholine is neurotransmitter at end
organ as well as at preganglionic synapse:
“cholinergic”

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Parasympathetic continued
Cranial outflow
III - pupils constrict
VII - tears, nasal mucus, saliva
IX – parotid salivary gland
X (Vagus n) – visceral organs of thorax & abdomen:
Stimulates digestive glands
Increases motility of smooth muscle of digestive tract
Decreases heart rate
Causes bronchial constriction
Sacral outflow (S2-4): form pelvic splanchnic nerves
Supply 2
nd
half of large intestine
Supply all the pelvic (genitourinary) organs

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Parasympathetic
(only look at this
if it helps you)

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Sympathetic nervous system
“fight, flight or fright”
Also called thoracolumbar system: all its neurons
are in lateral horn of gray matter from T1-L2
Lead to every part of the body (unlike parasymp.)
Easy to remember that when nervous, you sweat; when
afraid, hair stands on end; when excited blood pressure
rises (vasoconstriction): these sympathetic only
Also causes: dry mouth, pupils to dilate, increased heart
& respiratory rates to increase O2 to skeletal muscles,
and liver to release glucose
Norepinephrine (aka noradrenaline) is
neurotransmitter released by most postganglionic
fibers (acetylcholine in preganglionic): “adrenergic”

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Sympathetic nervous system continued
Regardless of target, all
begin same
Preganglionic axons exit
spinal cord through ventral
root and enter spinal nerve
Exit spinal nerve via
communicating ramus
Enter sympathetic
trunk/chain where
postganglionic neurons are
Has three options…

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Options of preganglionic axons in sympathetic trunk
1.Synapse on postganglionic neuron in chain
ganglion then return to spinal nerve and follow
its branch to the skin
2.Ascend or descend within sympathetic trunk,
synapse with a posganglionic neuron within a
chain ganglion, and return to spinal nerve at that
level and follow branches to skin
3.Enter sympathetic chain, pass through without
synapsing, form a splanchnic nerve that passes
toward thoracic or abdominal organs
These synapse in prevertebral ganglion in
front of aorta
Postganglionic axons follow arteries to organs
(see next slides for drawing examples)

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Synapse in chain ganglia
at same level or different level

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Pass through ganglia and synapse in
prevertebral ganglion

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Sympathetic

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Adrenal gland is exception
On top of kidneys
Adrenal medulla
(inside part) is a
major organ of
the sympathetic
nervous system

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Adrenal gland is exception
Synapse in gland
Can cause body-wide
release of epinephrine
aka adrenaline and
norepinephrine in an
extreme emergency
(adrenaline “rush” or
surge)

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Summary

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Visceral sensory system
Gives sensory input to
autonomic nervous
system

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Visceral sensory neurons
Monitor temperature, pain, irritation, chemical changes
and stretch in the visceral organs
Brain interprets as hunger, fullness, pain, nausea, well-being
Receptors widely scattered – localization poor (e.g.
which part is giving you the gas pain?)
Visceral sensory fibers run within autonomic nerves,
especially vagus and sympathetic nerves
Sympathetic nerves carry most pain fibers from visceral organs
of body trunk
Simplified pathway: sensory neurons to spinothalamic
tract to thalamus to cerebral cortex
Visceral pain is induced by stretching, infection and
cramping of internal organs but seldom by cutting (e.g.
cutting off a colon polyp) or scraping them

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Referred pain: important to know
Pain in visceral
organs is often
perceived to be
somatic in origin:
referred to somatic
regions of body that
receive innervation
from the same
spinal cord
segments
Plus left shoulder,
from spleen
Anterior skin areas to which pain is
referred from certain visceral organs

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Visceral sensory and autonomic neurons
participate in visceral reflex arcs
Many are spinal reflexes such as defecation
and micturition
reflexes
Some only
involve peripheral
neurons: spinal
cord not involved
(not shown)*
*e.g. “enteric” nervous system: 3 neuron reflex arcs entirely within the wall of the gut

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Central control of the
Autonomic NS
Amygdala: main limbic
region for emotions
-Stimulates sympathetic
activity, especially previously
learned fear-related behavior
-Can be voluntary when
decide to recall frightful
experience - cerebral cortex
acts through amygdala
-Some people can regulate
some autonomic activities by
gaining extraordinary control
over their emotions
Hypothalamus: main
integration center
Reticular formation:
most direct influence
over autonomic
function

27. HORNER’S SYNDROME
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28. Horner’s syndrome
Horner's syndrome (also known as Bernard-Horner syndrome and oculosympathetic palsy)
is a combination of symptoms that arises when a group of nerves known as the sympathetic trunk
is damaged. The symptoms occur on the ipsilateral side characterized by MIOSIS, PTOSIS,
ANHIDROSIS.
Signs that are found in patients on the affected side of the face include
partial ptosis : Weakness of the superior tarsal muscle
upside-down ptosis (slight elevation of the lower lid)
Anhidrosis
Miosis : Inactivation of the dilator pupillae
Enophthalmos : Weakness of the orbitalis muscle
loss of ciliospinal reflex
bloodshot conjunctiva, depending on the site of lesion.
In children, Horner's syndrome sometimes leads toheterochromia, a difference in eye color between
the two eyes. This happens because a lack of sympathetic stimulation in childhood interferes with
melanin pigmentation of the melanocytes in the superficial stroma of the iris.
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29. CAUSES
Due to lesion or compression of one side of the cervical or thoracic sympathetic chain, which
generates symptoms on the ipsilateral (same side as lesion) side of the body.
Lateral medullary syndrome
Cluster headache - combination termed Horton's headache
Trauma - base of neck, usually blunt trauma, sometimes surgery.
Middle ear infection
Tumors - often bronchogenic carcinoma of the superior fissure (Pancoast tumor) on apex of lung
Aortic aneurysm, thoracic
Neurofibromatosis type 1
Goiter
Dissecting aortic aneurysm
Thyroid carcinoma
Multiple sclerosis
Cervical rib traction on stellate ganglion
Carotid artery dissection
Klumpke paralysis
Cavernous sinus thrombosis
Sympathectomy
Syringomyelia
Nerve blocks, such as cervical plexus block, stellate ganglion or interscalene block
As a complication of tube thoracostomy
A Horner's syndrome may occur during a migraine attack and be relieved afterwards29

30. Pathophysiology
Horner syndrome is due to a deficiency ofsympathetic activity. The site of lesion to the
sympathetic outflow is on the ipsilateral side of the symptoms. The following are examples of
conditions that cause the clinical appearance of Horner's syndrome:
First-order neuron disorder: Central lesions that involve the hypothalamospinal tract (e.g.
transection of the cervical spinal cord).
Second-order neuron disorder: Preganglionic lesions (e.g. compression of the sympathetic chain
by a lung tumor).
Third-order neuron disorder: Postganglionic lesions at the level of the internal carotid artery (e.g.
a tumor in the cavernous sinus or a carotid artery dissection).
Partial Horner's syndrome In case of a third-neuron disorder, anhidrosis is limited to the middle
part of the forehead or can be absent, resulting in a partial Horner's syndrome.
If someone has impaired sweating above the waist affecting only one side of the body, yet they
do not have a clinically apparent Horner's syndrome, then the lesion is just below the stellate
ganglion in the sympathetic chain.
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31. DIAGNOSIS
Three tests are useful in confirming the presence and severity of Horner syndrome:
Cocaine drop test: Cocaine eyedrops block the reuptake of norepinephrine resulting in the
dilation of a normal pupil. However, in Horner's syndrome the lack of norepinephrine in the
synaptic cleft causes mydriatic failure. A more recently introduced approach that is more
dependable and obviates the difficulties in obtaining cocaine is to apply the alpha-agonist
apraclonidine to both eyes and observe the increased mydriatic effect (due to
hypersensitivity) on the affected side of Horner syndrome (the opposite effect to what the
cocaine test would produce in the presence of Horner's)
Paredrine test: This test helps to localize the cause of the miosis. If the third order neuron
(the last of three neurons in the pathway which ultimately discharges norepinephrine into
the synaptic cleft) is intact, then the amphetamine causes neurotransmitter vesicle release,
thus releasing norepinephrine into the synaptic cleft and resulting in robust mydriasis of the
affected pupil. If the lesion itself is of the third order neuron, then the amphetamine will
have no effect and the pupil remains constricted. There is no pharmacological test to
differentiate between a first and second order neuron lesion.
Dilation lag test
.
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32. It is important to distinguish the ptosis caused by Horner's syndrome from the ptosis caused by a
lesion to the oculomotor nerve. In the former, the ptosis occurs with a constricted pupil (due to a
loss of sympathetics to the eye), whereas in the latter, the ptosis occurs with a dilated pupil (due
to a loss of innervation to the sphincter pupillae). In a clinical setting, these two ptoses are fairly
easy to distinguish. In addition to the blown pupil in a CNIII (oculomotor nerve) lesion, this ptosis
is much more severe, occasionally occluding the whole eye. The ptosis of Horner syndrome can
be quite mild or barely noticeable (partial ptosis).
[citation needed]
When anisocoria occurs and the examiner is unsure whether the abnormal pupil is the
constricted or dilated one, if a one-sided ptosis is present then the abnormally sized pupil can be
presumed to be on the side of the ptosis.
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36. THANK YOU
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