Autonomic Nervous System

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About This Presentation

Autonomic Nervous System


Slide Content

The Autonomic Nervous System
Moderator
Dr. Gangaram
1

The critical component of central network involved in
homeostasis & adaptation
3 subdivisions :
●Sympathetic Nervous System
●Parasympathetic Nervous System
●Enteric Nervous System
Introduction

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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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Divisions of the autonomic nervous system

Parasympathetic division

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

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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
= ganglionic neuron (cell body in ganglion outside CNS)
●Slower because lightly or unmyelinated

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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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Anatomical Differences in Sympathetic
and Parasympathetic Divisions
Length of postganglionic fibers
–Sympathetic – long postganglionic fibers
–Parasympathetic – short postganglionic fibers
Branching of axons
–Sympathetic axons – highly branched
–Influences many organs
–Parasympathetic axons – few branches
–Localized effect

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Anatomical Differences in Sympathetic
and Parasympathetic Divisions

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Anatomical Differences in Sympathetic
and Parasympathetic Divisions

Comparison of Somatic and Autonomic Nervous
Systems
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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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

Synapse on postganglionic neuron in chain ganglion then
return to spinal nerve and follow its branch to the skin

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

Enter sympathetic chain, pass through without synapsing, form
a splanchnic nerve that passes toward thoracic or abdominal
organs

These synapses in prevertebral ganglion in front of aorta

Postganglionic axons follow arteries to organs

SPINAL SEGMENTS INNERVATION
T1 – T3 HEAD
T1 – T6 UPPER EXTREMITIES
THORACIC VISCERA
T5 – T11 ABDOMINAL VISCERA
T11 – L2 LOWER EXTREMITIES
PELVIC & PERINEAL ORGANS

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Sympathetic Pathways to Periphery
Figure 15.9

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Sympathetic Pathways to the Head

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Sympathetic Pathways to the Abdominal Organs

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Sympathetic Pathways to the Pelvic Organs

The Role of the Adrenal Medulla in the
Sympathetic Division
Major organ of the sympathetic nervous system
Secretes great quantities epinephrine (a little
norepinephrine)
Stimulated to secrete by preganglionic sympathetic
fibers

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The Adrenal Medulla

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Sympathetic Division of the ANS

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The Parasympathetic Division

Cranial Outflow
Preganglionic fibers run via:
–Oculomotor nerve (III)
–Facial nerve (VII)
–Glossopharyngeal nerve (IX)
–Vagus nerve (X)
Cell bodies located in cranial nerve nuclei in the brain
stem


Westphal nucleus is a part of occulomotor complex in
midbrain – sends preganglionic axons that occupy peripheral
portion of the occulomotor nerve and synapse on the neurons
of ciliary ganglion in the orbit

These neurons innervate iris and ciliary muscles

Eliciting pupil constriction, accomodation of eye


Superior salivatory nucleus –

In pons

projects via facial nerve to sphenopalatine ganglion, which
innervates - lacrimal gland ( lacrimation )
cerebral blood vessels ( vasodilatation )

to submandibular ganglion – secretomotor & vasodilator
inputs to corresponding salivary glands


Inferior salivatory nucleus –

In medulla

Sends axons via glossopharyngeal nerve

Synapse on Otic ganglion

Stimulate parotid gland secretion

Outflow via the Vagus Nerve (X)
Fibers innervate visceral organs of the
thorax and most of the abdomen
Stimulates - digestion, reduction in
heart rate and blood pressure
Preganglionic cell bodies
–Located in dorsal motor nucleus
in the medulla
Ganglionic neurons
–Confined within the walls of
organs being innervated


Vagus innervates heart, respiratory tract and entire
gastrointestinal tract except descending colon and rectum

Most vagal preganglionic neurons – situated in dorsal motor
nucleus of vagus provides input to git and respiratory
tracts, heart

Vagal preganglionic output to heart - Neurons in
ventrolateral portion of nucleus ambiguus

Vagus – cardioinhibitory, visceromotor and secretomotor
effects

Sacral Parasympathetic Outflow
•Consists of S2-S4.
•Pelvic splanchnic nerves
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Sacral preganglionic output –

Arises from neurons of sacral preganglionic nucleus located
in lateral gray matter of spinal segments S2 & S3

Their axons pass via ventral roots of pelvic splanchnic nerves
which join inferior hypogastric plexus

Innervate colon, bladder, sexual organs

Parasympathetic output – contraction of bladder detrussor
muscle & circular smooth muscle of rectum.


Sacral parasympathetic output elicits
Vasodilatation of cavernous tissue of penis
required for penile erection ,
whereas sympathetic output controls ejaculation

Autonomic Plexuses
•A network of sympathetic and parasympathetic axons.
•Cardiac plexus- heart.
•Pulmonary plexus- the bronchial tree.
•Celiac plexus- largest. Supplies the stomach, spleen,
pancreas, liver, gallbladder, and adrenal medullae.
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Autonomic Plexuses (Cont’d)..
•Superior mesenteric plexus- small intestine and proximal
colon.
•Inferior mesenteric plexus- distal colon and rectum.
•Hypogastric plexus- urinary bladder and genital organs.
•Renal plexus- kidneys and ureters.
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Enteric Nervous System

Includes several types of sensory neurons, inter-neurons,
motor neurons – which form integrative local reflex circuits

Controlling motility, secretion, blood flow throughout the gut

The activity of enteric nervous system is largely independent
of extrinsic innervation but is modulated by both vagal inputs
from dorsal vagal nucleus and sympathetic inputs from
prevertebral ganglia

Integration and Control of Autonomic
Functions
•Direct innervation- brain stem and spinal cord.
•Hypothalamus is the major control and integration center of
the ANS.
•It receives input from the limbic system.
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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

Components

Telencephalic structures –insular cortex
ant cingulate cortex
Amygdala

Insular cortex - integration of bodily sensation, emotion,
decision making

anterior cingulate cortex – motivation, goal directed
behavior

amygdala – conditioned fear responses


Hypothalamus – central role in integrating autonomic and
endocrine responses

Hypothalmus – critical role in adaptation to internal /
external stimuli, while maintaining homeostasis

3 zones

Paraventricular zone – neuroendocrine control via
connections to pituitary

Medial zone – thermoregulation, osmoregulation, food
intake, response to stress

Lateral zone – arousal behaviour, sleep wake cycle


Brain Stem Components –

Periaqueductal gray –

integration of autonomic, somatic and antinociceptive
responses to external stress.

coordinates cardiovascular, respiratory, thermoregulatory,
urinary, reproductive and pain control systems

Parabrachial nucleus – taste, salivation, gi activity,
cardiorespiratory activity, thermoregulation

NTS – 1
st
relay center for taste and visceral afferent
information carried in CN VII,IX,X
And also for all medullary, cvs, rs, gi reflexes

Visceral Afferents

Inform CNS about Mechanical & Chemical events in internal
organs

This information is conveyed to produce conscious visceral
sensation and initiate visceral reflex responses

Spinal visceral afferents innervate all peripheral organs

Their cell bodies are in dorsal root ganglion


Brain stem visceral afferents are carried primarily by
glossopharyngeal and vagus nerves

Cell bodies in petrosal & nodose ganglia

All brain stem visceral afferent nerves relay in nucleus of
solitary tract ( NTS )

NTS is a major site of information integration of many
bodily functions


Rostral portion of NTS – receives taste afferents via facial
nerve( geniculate ganglion ) , glossopharyngeal & vagus
nerves

Intermediate portion – receives gastrointestinal afferents

Caudal portion of the NTS recieves afferent information
from baroreceptors, cardioreceptors, chemoreceptors and
pulmonary receptors

Anatomical Differences in Sympathetic
and Parasympathetic Divisions (Recall)
Issue from different regions
of the CNS
–Sympathetic – also
called the
thoracolumbar division
–Parasympathetic – also
called the craniosacral
division

TARGET SYMPATHETIC PARASYMPATHETIC
PUPIL DILATATION ( A 1 ) CONSTRICTION (M3)
CILIARY MUSCLE … ACCOMODATION (M3)
SALIVARY &
LACRIMAL GLANDS
INHIBITION STIMULATION (M3)
HEART STIMULATION (B1) INHIBITION (A2)
BRONCHI DILATATION (B1) CONSTRICTION (M3)
SWEAT GLANDS STIMULATION (M3)
GI MOTILITY INHIBITION (B2) CONTRACTION (M3)
RELAXATION (NO,VIP)
BLADDER DETRUSSOR INHIBITION (B2) STIMULATION (M3,M2)
RECTAL SM INHIBITION (B2) STIMULATION (M3)
ERECTILE TISSUE CONSTRTICTION (A1) DILATATION (NO)

Horner's syndrome
●Interruption of sympathetic supply to head and neck
●Constriction of pupil
●Drooping of upper eyelid
●Reduced prominance of eye(enophthalmous)
●anhydrosis

Dysautonomic polyneuropathy
●Rare, both sympathetic and parasympathetic are affected at
post ganglionic level
●Somatosensory and motor nerves spared

Primary
●Middle aged
●Post-ganglionic
sympathetic
●Parasympathetic spared
Orthostatic hypotension
Secondary
●ANS impairment as a part
of peripheral neuropathy
●Afferent pathways or post
ganglionic sympathetic
fibres in spinal nerves
●Eg GBS, porphyrias, DM,
alcoholic, nutritional
Orthostatic hypotension
Anhydrosis, orthostatic hypotension, impotency, atonicity of
bladder

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Summary

Thank you
Dr. Shirisha


Autonomic lab tests :

impaired sudomotor axon reflex response

reduced variation of heart rate to deep breathing

reduced valsalva ratio

orthostatic hypotension

gi motility – delayed gastric emptying

usg post void urine – 250 cc