Autonomic nervous system Physiology

Central nervous system
• The nervous system with the endocrine
system controls and coordinates various
functions of the body.
• The body has to make adjustments
according to the changes in its internal
and external environments.
• These adjustments are essential for the
maintenance of homeostasis, as well as
for existence.

The nervous system can be classified:
• Anatomically, according to its
different structures,
• Physiologically, according to its
functions.
Anatomically nervous system formed of
(Somatic nervous system, autonomic
nervous system and integrative nervous
system).

Nervous System
Peripheral NS Central NS
Efferent Division Afferent Division
Autonomic Somatic
Sympathetic Parasympathetic

Peripheral Nervous System
• Handles the CNS’s input and output.
• Contains all the portions of the NS
outside the brain and spinal cord.
• Contains sensory nerves and motor
nerves
• Divided into autonomic nervous
system and somatic nervous
system.

• Sensory Nerves
(to the brain)
Carry messages from
receptors in the skin,
muscles, and other
internal and external
sense organs to the
spinal cord and then
to the brain
• Motor Nerves
(from the brain)
Carry orders from CNS
to muscles, glands to
contract and produce
chemical
messengers

• The ANS is part of the peripheral nervous
system and it controls many organs and
muscles within the body.
• In most situations, we are unaware of the
workings of the ANS because it functions in
an involuntary, reflexive manner.
• For example, we do not notice when blood
vessels change size or when our heart beats
faster.
• However, some people can be trained to
control some functions of the ANS such as
heart rate or blood pressure.

The ANS is most important in two situations:
1- In emergencies that cause stress
and require us to "fight" or take
"flight" (run away).
2- In no emergencies that allow us
to "rest" and "digest".

DefinitionDefinition
The portion of the nervousThe portion of the nervous
system that controls mostsystem that controls most
visceral functions of the body isvisceral functions of the body is
called thecalled the autonomic nervousautonomic nervous
system (ANS).system (ANS).
12:11 drsherwanshal@gmail.com 11

DefinitionDefinition
Or it is the motor nervousOr it is the motor nervous
system that controls glands,system that controls glands,
cardiac muscle, and smoothcardiac muscle, and smooth
muscle.muscle.

The primary target organs of theThe primary target organs of the
ANSANS
The viscera of the thoracic andThe viscera of the thoracic and
abdominal cavities andabdominal cavities and
some structures of the bodysome structures of the body
wall, including cutaneous bloodwall, including cutaneous blood
vessels, sweat glands, andvessels, sweat glands, and
piloerector muscles.piloerector muscles.

ControlControl
Autonomic literallyAutonomic literally
means “self-governed.”.means “self-governed.”.
TheThe ANS usually carries out itsANS usually carries out its
actions involuntarily, without ouractions involuntarily, without our
conscious intent or awareness, inconscious intent or awareness, in
contrast to the voluntary nature ofcontrast to the voluntary nature of
the somatic motor system.the somatic motor system.

Visceral effectorsVisceral effectors
Visceral effectors do not dependVisceral effectors do not depend
on the ANS to function, but onlyon the ANS to function, but only
to adjust their activity to theto adjust their activity to the
body’s changing needs.body’s changing needs.

The heart, for example, goes onThe heart, for example, goes on
beating even if all autonomicbeating even if all autonomic
nerves to it are severed, but thenerves to it are severed, but the
ANSANS modulates (adjusts) themodulates (adjusts) the
heart rate in conditions ofheart rate in conditions of restrest
or exercise.or exercise.

If the somatic nerves to aIf the somatic nerves to a
skeletal muscle are severed, theskeletal muscle are severed, the
muscle exhibits flaccidmuscle exhibits flaccid
paralysis—it no longerparalysis—it no longer
functions.functions.

But if the autonomic nerves toBut if the autonomic nerves to
cardiac or smooth muscle arecardiac or smooth muscle are
severed, the muscle exhibitssevered, the muscle exhibits
exaggerated responsesexaggerated responses
(denervation hypersensitivity).(denervation hypersensitivity).

striking characteristics of the ANS
The rapidity and intensity.
For instance,
Within 3 to 5 seconds it can increase the heart rate
to twice normal.
Within 10 to 15 seconds the arterial pressure can
be doubled.
The arterial pressure can be decreased low
enough within 10 to 15 seconds to cause fainting.
Sweating can begin within seconds, and the
urinary bladder may empty involuntarily, also within
seconds.

Autonomic System
• Two divisions:
– sympathetic
– Parasympatheitic
• Control involuntary functions
– heartbeat
– blood pressure
– respiration
– perspiration
– digestion
• Can be influenced by thought and
emotion

• It is usual to divide the nervous
system into somatic, autonomic and
integrated systems.
• The somatic nervous system provides
voluntary motor control of skeletal
muscle.
• The autonomic nervous system
provides an involuntary control of
internal environment and the viscera.

• Somatic NS
Consists of nerves
connected to
sensory
receptors and
skeletal muscles
Permits voluntary
action (writing
your name)
• Autonomic NS
Permits the
Involuntary functions
of blood vessels,
Glands and
internal organs e.g.:-
the bladder
stomach
heart

Characteristic Somatic nervous
system
Autonomic N.
system
Effectors Voluntary muscle Cardiac muscle
glands, s. muscle
General functions Adjustment to
external environment
Adjustment within
internal environment
Numbers of neurons 1 2
Ganglia outside the
CNS
------------ Chain ganglia,
collateral ganglia or
terminal ganglia
Neurotransmitter acetylcholine Acetylcholine,
adrenaline,
noradrenaline
Center Anterior Horn cells Lateral Horn cells

Comparison of Somatic and ANSComparison of Somatic and ANS

Comparison of Autonomic and
Somatic Motor Systems
• Autonomic nervous system
– Chain of two motor neurons
• Preganglionic neuron
• Postganglionic neuron
– Conduction is slower due to thinly or
unmyelinated axons
Pre-ganglionic
Ganglion
Post-ganglionic

Sympathetic N.S. Parasympathetic N.S.
Like the accelerator of
your car
Like the brakes in your car
Slows the body down to
keep its rhythm
Mobilized the body for
action
Enables the body to
conserve and store energy
Preganglionic: short, synapse
within the lateral & collateral
ganglia
Preganglionic: long, synapse
within the terminal ganglia
Postganglionic: long Postganglionic: short
Has a wide distributions Has a restricted distributions

Autonomic Nervous System
• Often work in
opposition
• Cooperate to fine-
tune homeostasis
• Regulated by the
brain;
hypothalamus, pons
and medulla
• Can also be
regulated by spinal
reflexes; no higher
order input
• Pathways both
consist of a two
neuron system
Preganglionic neuron autonomic ganglion postganglionic neuron target
from CNS outside CNS

ANATOMY
1) SYMPATHETIC
(THORACOLUMBAR) DIVISION.
2 ) PARASYMPATHETIC
(CRANIOSACRAL) DIVISION.

General Organization of the ANSGeneral Organization of the ANS
The EFFERENTEFFERENT autonomic signals are
transmitted to the various organs of the
body through two major subdivisions called
The sympathetic nervous system.sympathetic nervous system.
The parasympathetic nervous parasympathetic nervous
systemsystem.

SympatheticSympathetic
Nervous SystemNervous System

Physiologic Anatomy of the Sympathetic NSPhysiologic Anatomy of the Sympathetic NS

Each sympathetic pathwaysympathetic pathway from the cord
to the stimulated tissue is composed of
two neuronstwo neurons, a preganglionic neuron preganglionic neuron
and a postganglionic neuronand a postganglionic neuron, in contrast
to only a single neuron in the skeletal
motor pathway.

Sympathetic Division of the ANS

ParasympatheticParasympathetic
Nervous SystemNervous System

Physiologic Anatomy of thePhysiologic Anatomy of the
Parasympathetic Nervous SystemParasympathetic Nervous System
 Parasympathetic fibers leave the CNS
through cranial nerves III, VII, IX, and XIII, VII, IX, and X.
 Additional parasympathetic fibers leave
the lowermost part of the spinal cord
through the second and third sacralsecond and third sacral
spinalspinal nerves and occasionally the first
and fourth sacral nerves.

Physiologic Anatomy of thePhysiologic Anatomy of the
Parasympathetic Nervous SystemParasympathetic Nervous System
About 75 per cent of all parasympathetic
nerve fibers are in the vagus nerves vagus nerves
(cranial nerve X), passing to the entire
thoracic and abdominal regions of the
body.
Therefore, a physiologist speaking of the
parasympathetic nervous system often
thinks mainly of the two vagus nerves.

Sympathetic
• Sometimes called the
“thoracolumbar” division
• Short preganglionic neurons;
long postganglionic neurons;
ganglia are called the chain
ganglia
• Preganglionic neurons secrete
Ach onto nicotinic receptors
• Postganglionic neurons
secrete NE on to α or β
receptors
• Target tissues are smooth
muscle, cardiac muscle,
endocrine glands, brown fat

Parasympathetic
•Sometimes called the
“cranio-sacral division
•Long preganglionic
neurons;
•short postganglionic
neurons (often in the
target organ)
•Preganglionic neurons
secrete Ach on to
nicotinic receptors
•Postganglionic neurons
secrete Ach on to
muscarinic receptors
•Target tissues are
smooth muscle,
cardiac muscle,
exocrine glands, brown
fat

Anatomical Differences in Sympathetic
and Parasympathetic Divisions

Similarities between Sympathetic & ParasympatheticSimilarities between Sympathetic & Parasympathetic
• Both are efferent (motor) systems: “visceromotor”
• Both involve regulation of the “internal” environment
generally outside of our conscious control:
“autonomous”
• Both involve 2 neurons that synapse in a peripheral
ganglion and Innervate glands, smooth muscle,
cardiac muscle
CNS ganglion
preganglionic
neuron
postganglionic
neuron
glands
smooth
muscle
cardiac
muscle

Differences between Sympathetic & ParasympatheticDifferences between Sympathetic & Parasympathetic
Location of Preganglionic Cell Bodies
Thoracolumbar
T1 – L2/L3 levels
of the spinal cord
Craniosacral
Brain: CN III, VII, IX, X
Spinal cord: S2 – S4
Sympathetic Parasympathetic

Sympathetic
CNS ganglion
short preganglionic
neuron
long postganglionic
neuron
target
Parasympathetic
CNS ganglion
long preganglionic
neuron
target
short postganglionic
neuron
Relative Lengths of Neurons

Parasympathetic
Overview of the Autonomic Nervous SystemOverview of the Autonomic Nervous System
Neurotransmitters
ACh, +
NE (ACh at sweat glands),
+ / -, α & ß receptors
ACh, + / -
muscarinic receptors
• All preganglionics release acetylcholine (ACh) & are excitatory (+)
• Symp. postgangl. — norepinephrine (NE) & are excitatory (+) or inhibitory (-)
• Parasymp. postgangl. — ACh & are excitatory (+) or inhibitory (-)
Sympathetic
• Excitation or inhibition is a receptor-dependent & receptor-mediated response
ACh, +

Overview of the Autonomic Nervous SystemOverview of the Autonomic Nervous System
Target Tissues
ParasympatheticSympathetic
• Organs of head, neck,
trunk, & external genitalia
• Organs of head, neck,
trunk, & external genitalia
• Adrenal medulla
• Sweat glands in skin
• Arrector muscles of hair
• ALL vascular smooth muscle
» Sympathetic system is distributed to essentially all
tissues (because of vascular smooth muscle)
» Parasympathetic system never reaches limbs or
body wall (except for external genitalia)

Overview of ANSOverview of ANS
Functional Differences
Sympathetic
• “Fight or flight”
• Catabolic (expend energy)
Parasympathetic
• “Feed & breed”, “rest &
digest”
• Homeostasis
» Dual innervation of many
organs — having a brake
and an accelerator provides
more control

55
FUNCTION OF
PARASYMPATHETIC
&
SYMPATHETIC
NEVOUS SYSTEM

57
Sympathetic Nervous System
Main functions of the SNS
• Regulation of cardiovascular system
• Regulation of body temperature
• Implementation of “fight or flight” reaction
• FIGHT OR FLIGHT RESPONSE
• Stressful Situations ----
trauma, fear , hypoglycemia.

Sympathetic
• “ Fight or flight” response
• Release adrenaline and
noradrenaline
• Increases heart rate and
blood pressure
• Increases blood flow to
skeletal muscles
• Inhibits digestive functions

somatic tissues
(body wall, limbs)
visceral tissues
(organs)
Sympathetic System: Preganglionic Cell BodiesSympathetic System: Preganglionic Cell Bodies
• Preganglionic cell bodies in
intermediolateral gray
• T1 — L2/L3
• Somatotopic organization
intermediolateral
gray columns
lateral
horn
T1 –
L2/L3
Clinical Relevance
» dysfunction due to cord injury
» spinal nerve impingement & OMM
» referred pain

spinal
nerve
dorsal
ramus
ventral
ramus
gray ramus
communicans white ramus
communicans
sympathetic
ganglion
intermediolateral
gray column
Structure of spinal nerves: Sympathetic pathwaysStructure of spinal nerves: Sympathetic pathways

Sympathetic System: Postganglionic Cell BodiesSympathetic System: Postganglionic Cell Bodies
Paravertebral
ganglia
Prevertebral
ganglia
• celiac ganglion
• sup. mesent. g.
• inf. mesent. g.
aorta
sympathetic
trunk (chain)
1. Paravertebral ganglia
• Located along sides of vertebrae
• United by preganglionics into Sympathetic Trunk
• Preganglionic neurons are thoracolumbar (T1–L2/L3)
but postganglionic neurons are cervical to coccyx
• Some preganglionics ascend or descend in trunk
synapse at
same level
ascend to
synapse at
higher level
descend to
synapse at
lower level

Sympathetic System: Postganglionic Cell BodiesSympathetic System: Postganglionic Cell Bodies
Paravertebral
ganglia
Prevertebral
ganglia
• celiac ganglion
• sup. mesent. g.
• inf. mesent. g.
aorta
sympathetic
trunk (chain)
2. Prevertebral (preaortic) ganglia
• Located anterior to abdominal aorta, in plexuses
surrounding its major branches
• Preganglionics reach prevertebral ganglia via
abdominopelvic splanchnic nerves
abdominopelvic
splanchnic
nerve

Sympathetic System: SummarySympathetic System: Summary
T1
L2
4- somatic
tissues
(body wall, limbs)
visceral tissues
(organs)
postganglionics
via 31 spinal
nerves
to somatic tissues
of neck, body wall,
and limbs
sympathetic
trunk
prevertebral
ganglia
2- Cardiopulmonary
Splanchnics: postganglionic
fibers to thoracic viscera
3- Abdominopelvic
Splanchnics: preganglionic
fibers to prevertebral ganglia,
postganglionic fibers to
abdominopelvic viscera
1- Cervical division

1- Cervical division
Origin: T1-2
Course: preganglionic fibres reach the sympathetic
chain and then ascend upwards to relay
in the superior cervical ganglion.
Postganglionic neuron: pass from ganglion
to the following organs:-
• EYE: pupil dilatation, widening of palpebral fissure, exophthalmos,
Vasoconstriction of eye b.v. and Relaxation of ciliary muscle.
• Salivary gland : trophic secretion, Vasoconstriction of its blood vessels and
Squeezing of salivary secretion.
• Lacrimal gland: Trophic secretion and Vasoconstriction.
• Face skin blood vessel: Vasoconstriction of (Pale color).
• Sweet secretion: copious secretion.
• Hair: erection due to contraction of erector pilae muscles..
• Cerebral vessels: Weak vasoconstriction

Sympathetic Pathways to the Head

(2) Cardiopulmonary division
Origin: Lateral horn cells of upper 4-5 thoracic segments.
Course: Preganglionic neurons reach the sympathetic chain to
relay in the three cervical ganglion and upper four thoracic
ganglion.
The postganglionic arise from these ganglia supply the
following structures:-
• Heart: Increase all properties of cardiac muscle (contraction,
rhythmicity, excitability, conductivity.
• Coronary vessels, its sympathetic supply. At first it
causes vasoconstriction, and then it causes vasodilatation due
to accumulation of metabolites.
• Bronchi: Broncho dilation, decrease bronchial secretions and
vasoconstriction of pulmonary blood vessels.

Sympathetic Pathways to Thoracic
Organs

3- Splanchnic division
Origin: lateral horn cells of the lower six thoracic and upper four lumber segments.
Course: Preganglionic neurons originate from these segments reach the sympathetic
chain where they pass without relay, and then they divided into two branches:
(1) Greater splanchnic nerve
(2) Lesser splanchnic nerve.
Greater splanchnic nerve:
• Origin: Preganglionic nerves fibers emerge from lateral horn cells of lower six
thoracic segments and then relay in the collateral ganglion in the abdomen.
• Course: Postganglionic nerve fibers arise from these ganglia (celiac, superior
mesenteric and inferior mesenteric ganglia) and supply the abdominal organs
causing the following effects:
• Vasoconstriction: of most arteries of stomach, small intestine, proximal part of large
intestine, kidney, pancreas and liver.
• Relaxation of the musculature of: stomach, small intestine and proximal part of
large intestine.
• Contraction of sphincters: of the stomach and intestine leading to (food retention).
• Contraction of the capsule: of the spleen leading to evacuation of about 200 ml of
blood.
• Breakdown of the glucose in the liver: (glycogenolysis) leading to increase of
blood glucose level.
• Stimulation of adrenal medulla: Secrete adrenaline and noradrenalin.

Sympathetic Pathways to the Abdominal
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

Lesser splanchnic nerve
Origin: Preganglionic nerve fibers originate from the lateral horn
cells of the 12 thoracic and upper two lumber segments.
Course: 2 nerves from both sides unite together forming the
presacral nerve, which proceeds to pelvis and divided into two
branches (hypogastric nerves), then relay in the inferior
mesenteric ganglion.
Postganglionic nerve fiber supplies the following pelvic viscera:
Urinary bladder: Relaxation of its wall.
– Contraction of internal urethral sphincter.
– Leading to urine retention.
Rectum:
– Relaxation of the distal part of large intestine.
– Relaxation of the rectum wall.
– Contraction of the internal anal sphincter.
– Leading to feces retention.

Genital organs:
- Vasoconstriction of its blood vessels.
–Leading to shrinkage of penis and
clitoris.
Vas deferens:
- Contraction of its wall, and wall of
seminal vesicles, ejaculatory ducts and
prostate
- Leading to ejaculation.

Sympathetic Pathways to the Pelvic
Organs

(4) Somatic division
Origin: Preganglionic nerve fibers arise from all lateral
horn cells of all sympathetic segments, and then relay
in the cervical and sympathetic chain ganglia.
Course: Postganglionic nerve fibers emerge from these
ganglia proceeds outside the central nervous system
to return back to spinal cord to join the spinal nerve
when it comes out from the anterior horn cells, and
supply the following structures:
Skin:
• Vasoconstriction giving the pale color of the skin.
• Stimulation of the sweet glands, the eccrine glands give copious
secretion, while the apocrine glands give thick odoriferous secretion.
• Hair erection.
Skeletal muscle:
• Its blood vessels show vasodilatation (V.D.) due to cholinergic
effect or vasoconstriction (V.C.) due to a adrenergic effect.
• The type of stimulation depends upon the nature of stimulation.
• Muscles: its stimulation causing delayed fatigue and early recovery.

4- somatic tissues
(body wall, limbs)
postganglionics
via 31 spinal nerves
to somatic tissues of neck,
body wall, and limbs
sympathetic
trunk

Sympathetic Pathways to Periphery
Figure 15.9

80
ORGANS RECEIVING ONLY SYMPATHETIC
INNERVATION
• Adrenal Medulla
• Kidney
• Pilomotor muscles
• Sweat glands
• Vessels
• Metabolic processes

Fig. 45.34(TE Art)Hypothalamus activates
sympathetic division of
nervous system
Heart rate, blood pressure,
and respiration increase
Blood flow to
skeletal muscles
increases
Stomach
contractions
are inhibited
Adrenal medulla
secretes
epinephrine and
norepinephrine

Flight or fight reaction
• Acceleration of heart and lung action
• Inhibition of stomach and intestinal action
• Constriction of blood vessels in many parts of
the body
• Liberation of nutrients for muscular action
• Dilation of blood vessels for muscles
• Inhibition of tear glands and salivation
• Dilation of pupil
• Relaxation of bladder
• Inhibition of erection

83
Parasympathetic Nervous
System (PNS)
• Rest & Digest situations.
The regulatory functions of PNS affect these sites
• Heart rate
• Gastric secretions
• Bladder and bowel
• Vision
• Bronchial smooth muscle

Parasympathetic
• “ Rest and digest
” system
• Calms body to
conserve and
maintain energy
• Lowers heartbeat,
breathing rate,
blood pressure

ParasympatheticParasympathetic
PathwaysPathways
Cranial outflow
• CN III, VII, IX, X
• Four ganglia in head
• Vagus nerve (CN X) is major
preganglionic parasymp.
supply to thorax & abdomen
• Synapse in ganglia within
wall of the target organs (e.g.,
enteric plexus of GI tract)
Sacral outflow
• S2–S4 via pelvic splanchnics
• Hindgut, pelvic viscera, and
external genitalia
Clinical Relevance
» Surgery for colorectal cancer
puts pelvic splanchnics at risk
» Damage causes bladder &
sexual dysfunction

The Parasympathetic Division
• Cranial outflow
– Comes from the brain
– Innervates organs of the head, neck, thorax,
and abdomen
• Sacral outflow
– Supplies remaining abdominal and pelvic
organs

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

Sacral Outflow
Origin: Preganglionic nerve fibers arise from the
lateral horn cells of the 2nd, 3rd and 4th sacral
segments.
Course: These preganglionic passes without relay,
then the right and left branches unit together to form
the pelvic nerve, the pelvic nerve relay in the
terminal ganglia, where the postganglionic nerve
fibers emerge and supply the following structures:-
Urinary bladder: parasympathetic stimulation
causes:
- Contraction of the bladder wall
- Relaxation of its sphincter.
- These responses lead to micturition.

Rectum and descending colon:
parasympathetic stimulation causes:
- Contraction of its wall.
- Relaxation of internal anal sphincter.
- These responses lead to defecation.
Seminal vesicles and prostate:
parasympathetic stimulation -causes:
- Secretion of these glands.
Erectile tissue: parasympathetic stimulation
causes:
- Vasodilatation which lead to erection.

Comparison of sympathetic and
Parasympathetic Pathways
• Neurotransmitters
• Receptors

Sympathetic receptors
Adrenergic
receptors
Alpha Beta
Alpha 1 Alpha 2 Beta 1
Beta 3
Beta 2

103
ACTIONS OF CHOLINERGIC AGONIST
• CVS:
The action of Ach on heart mimic the effects of VAGAL
stimulation.
  The normal vagal activity regulates the
heart by
• release of Ach at SA node.
  Vasodilatation
  Decrease in heart rate ( -ve chronotropic effect).
  Decrease in force of contraction ( -ve Inotropic
• effect).
  Decrease in rate of conduction in SA & AV
• nodes ( -ve dromotropic effect).

104
Opposing effects of parasympathetic and
sympathetic nerves.

Summary of autonomic
differences
Autonomic nervous system controls physiological arousal
Sympathetic
division (arousing)
Parasympathetic
division (calming)
Pupils dilate EYES Pupils contract
Decreases SALVATION Increases
Perspires SKIN Dries
Increases RESPERATION Decreases
Accelerates HEART Slows
Inhibits DIGESTION Activates
Secrete stress
hormones
ADRENAL
GLANDS
Decrease secretion
of stress hormones

Autonomic nervous system Physiology

Autonomic nervous system Physiology

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