AUTONOMIC NERVOUS
SYSTEM
Terminologies for ANS
• Anatomically:
– Thoracolumber outflow(T1-L2)
– Craniosacral outflow(III, VII, IX, X, S1-S3)
• Physiologically:
– Sympathetic
– Para sympathetic
• Pharmacologically:
– Adrenergic
– Cholinergic
Somatic Vs ANS
Organization of ANS
• Central component:
1. Brainstem
2. Hypothalamus
3. Spinal cord
• Peripheral component:
1. Nerves
1.
2.
Sympathetic
Parasympathetic
• Ganglia:
1. Vertebral
2. Paravertebral
3. Terminal
Role of ANS
Maitain homeostasis by maintaining a dynamic
antagonism b/w sympathetic & parasympathetic
divisions of ANS
• Parasympathetic (D)
– Digestion
– Defecation
– Diuresis
• Sympathetic (E)
–
–
–
–
Exercise
Excitement
Emergency
Embarrassment
• Sympathetic system:
– Short preganglionic fiber
– Long postganglionic fiber
• Parasympathetic system:
– Long preganglionic fiber
– Short post ganglionic fiber
Autonomic neurotransmitters
• Acetylcholine (Cholinergic fibers)
– All preganglionic fibers
– All parasympathetic postganglionic fibers
• Adrenaline (Adrenergic fibers)
– Most sympathetic postganglionic fibers
Receptors
• Acetylcholine:
– Muscarinic
• Membranes of effecter cell
– Nicotinic
• Synapse of pre & post ganglionic autonomic nerves
• Adrenaline:
– Alpha
• Smooth muscles(contraction)
– Beta
• Smooth muscle(relaxation)
Sympathetic nerve fibers in
skelatal nerves
• Some of the sympathetic postganglionic fibers
pass back from sympathetic chain
• These are C type fibers
• Control
– Blood vessels
– Sweat glands
– Piloerector muscle
8% of fibers in skeletal nerves are sympathetic
Sympathetic nerve fibers in
adrenal medulla
• Preganglionic symp. Fibers pass without
synapse in adrenal medulla.
• Reach the specialized secretory cells which
secrete epinephrine & nor epinephrine.
Thank you
Functions of ANS
Sympathetic nervous system
Catabolic
Parasympathetic nervous system
Anabolic
Preserve energy in the body (i.e. save
Increases energy expenditure of the body. energy in the heart and offer it in the
intestine).
Prepares the body for activity, increasing
Predominates during sleep where there
the capacity to perform sever muscular
are continuous digestion, slow heart rate
effort (fight and flight) in response to
and constricted pupil.
stress (emergency situations).
Delay onset of fatigue of contracting Allow for repair and
muscles
contracting muscles.
Sympathetic mass stimulation is useful
recovery
of
Parasympathetic mass stimulation is fatal.
Eyes
• Pupillary opening
– Sympathetic system:
• Contracts meridional fibers--- pupillary dilatation
– Parasympathetic system:
• Contracts the circular muscles---- pupillary constriction
• Focus of lense:
– Parasympathetic:
• Contracts ciliary muscles---- release of tension in lense
ligament---- convex---- accomodation
Glands
• Nasal, lacrimal, salivary & gastrointestinal
glands
• Parasympathetic---- increased secretion
• Sympathetic ---- concentrated
secretions(enzymes & mucous)
• Sweat glands: cholinergic sympathetic fibers---- increased secretion
– Stimulated by centers in hypothalamus
• Apocrine glands
– Supplied by sympathetic fibers
– Stimulation secretes thick, odriferous & lubricant
secretion
GIT
• Parasympathetic:
– Increases motility
– Sphincters relax
– Increased secretion of glands
• Sympathetic:
– Strong stimulation
• Inhibits peristalsis
• Increased sphincters tone
(1) GIT
• (Stomach, small intestine and proximal part of large
intestine)
• Relaxation of their walls and contraction of their sphincters
leading to inhibition of digestion and delayed evacuation of
their contents.
(2) Liver:
• Stimulation of glycogenolysis leading to increased blood
glucose.
• Stimulation of fibrinogen synthesis.
(3) Gall bladder:
• contraction of wall and relaxation of sphincter of Oddi,
helping its evacuation.
(4) Spleen:
• Contraction of smooth muscles in splenic capsule and
trabeculae leading to pouring of about 250 ml of stored
blood into the general circulation.
(5) Pancreas:
• Sympathetic stimulation usually inhibits pancreatic secretion
(both endocrine and exocrine components).
(6) Blood vessels
• Mixed supply (vasoconstriction and vasodilatation).
(7) Kidneys:
• Stimulation of juxta glomerular cells leading to increased
renin secretion.
• Decrease renal blood flow.
• Decrease urine output.
Sympathetic
origin
LHCs of T6-12
segments of
spinal cord
(splanchni
c nerves).
Relay
Collateral
ganglia (celiac,
superior
mesenteric,
aortico-renal)
and terminal
ganglia
(1) GIT
• (Stomach, small intestine and proximal part of large
intestine)
• contraction of their walls and relaxation of their sphincters
enhancing both digestion and evacuation of GIT contents i.e.
help deglutition, gastric motility, and peristaltic movement of
GIT.
(2) Liver:
• increased hepatic bile flow.
(3) Gall bladder:
• Relaxation of its wall and contraction of sphincter of oddi
leading to retention of bile and delayed emptying of gall
bladder.
(4) Pancreas:
• Parasympathetic stimulation usually stimulates pancreatic
secretion (both endocrine and exocrine components).
(5) Blood vessels
• Vasodilatation.
(6) Glands:
• Stimulation of gastric juice secretion (rich in HCl).
• Stimulation of alkaline mucus secretion from Bruner's glands
in the duodenum.
Parasympatheti
c
origin
Dorsal
motor
nucleus of
the vagus
Relay
Terminal
ganglia in
the wall of
abdominal
organs
Action of sympathetic on Suprarenal medulla
Origin: LHCs of T10,11 segments of spinal cord.
* SRM has special character being supplied by sympathetic preganglionic nerve
fibers (with no postganglionic nerve fibers) which relay there on special
neurosecretory cells (chromaffin cells).
* Stimulation of sympathetic nerves to SRM releases large quantities of
adrenaline (80%) and noradrenaline (20%) into the circulating blood, being
carried to all body tissues. These hormones has prolonged action due to their
slow clearance from the circulation.
- Adrenaline acts more on metabolic actions of the body while noradrenaline
acts more on blood vessels.
- In stress conditions, SRM acts together with sympathetic nervous system
(sympatho-adrenal system).
Heart (CVS)
Sympathetic
• Increased HR
• Increased FOC
• Increased resistance
• Vasoconstriction in abdomin
& skin
Parasympathetic
• Decreased HR
• Decreased FOC
• Decreased resistance
• Little effect on vessels
Sympathetic
Parasympathetic
Origin
LHCs of upper 4 or 5 thoracic segments Dorsal Motor nucleus of the vagus
of spinal cord
Relay
Cervical ganglia (superior, middle and Terminal ganglia in the wall of the heart
inferior) and upper 4 thoracic ganglia
and lung
a) Sympathetic stimulation increases the Parasympathetic stimulation decreases
effectiveness of the heart as a pump i.e. the effectiveness of the heart as a pump
increasing the rate, force of heart i.e. decreasing the rate, force of heart
contraction,
Action on
the heart
conduction
velocity, contraction,
conduction
velocity,
excitability, cardiac metabolism and O2 excitability, cardiac metabolism and O2
consumption.
consumption.
b) Coronary vessels: Direct effect is  Coronary vessels : Direct effect is
vasoconstriction. Indirectly the coronary vasodilatation. Vagal stimulation inhibits
vessels dilate as a result of accumulation cardiac work with less production of
of metabolites of the stimulated heart.
metabolites. Thus the coronary vessels
indirectly constrict (vasoconstriction).
 N.B.: Parasympathetic does not supply the ventricles.
SYMPETHETIC
PARASYMPETHETIC
a) inhibition of the smooth a) Motor to the smooth
muscles of the bronchial muscles of the bronchial tree
tree
Action
of the
lungs
resulting
bronchodilatation
in resulting
in
bronchoconstriction.
b) inhibition of the mucus
b)
secretion of air passages.
c) vasoconstriction of the
pulmonary blood vessels.
secretion of the air passages.
c)
Stimulate
the
Vasodilatation
mucus
of
pulmonary blood vessels.
the
Actions on Pelvis
Sympathetic
Parasympathetic
Origin
LHCs of L1, L2, L3 segments of spinal cord. Sacral segments 2, 3, 4 (preganglionic
forms pelvic nerve)
Relay
Collateral ganglia (inferior mesenteric or
hypogastric ganglia) and terminal ganglia
Action on
Urinary
bladder
Contraction of its wall and relaxation of
relaxation of its wall and contraction of
internal urethral sphincter leading to
internal urethral sphincter leading to
micturition.
urine retention.
Terminal ganglia in the wall of the pelvic
organs
relaxation of its wall and contraction of Contraction of its wall and relaxation of
anal sphincter leading to internal anal sphincter leading to
retention.
defecation.
Action of
internal
the rectum
Action of
male sex
organs
Action of
a) Contraction of smooth muscles in a) Vasodilatation of the blood vessels of
the walls of seminal vesicle,
the pelvic viscera including that of sex
epididymis,
vas
deferens
and
organs leading to erection of the penis,
ejaculatory duct leading to ejaculation
clitoris, etc. and congestion of the
of semen.
labia. So, the pelvic nerve is named as
b) Vasoconstriction of blood vessels of
the nervus erigenus.
pelvic viscera including those of b) Secretory to the seminal vesicles,
external sex organs leading to
prostate and other accessory glands.
shrinkage of penis.
a) Vasoconstriction of blood vessels of
Sympathetic
(I) Antagonistic functions:
1- Pupil:
Mydriasis.
2- Air passages.
bronchodilatation.
3- Heart
 rate
Parasympathetic
Miosis.
bronchoconstriction.
 rate
 contraction
 coronary blood flow
 contraction
 coronary blood flow
4- GIT:
- Wall
- Sphincter
- Blood vessels
5- Rectum
relaxation
contraction
vasoconstriction
retention of faeces
contraction
relaxation
vasodilatation
defecation
6- Urinary bladder
7- blood vessels
retention of urine
Vasoconstriction
Micturition
vasodilatation
(II) Synergistic function: (During salivary secretion)
Trophic salivary secretion
(little, viscid, rich in enzymes)
True salivary secretion
(large in volume, watery, rich in electrolytes)
N.B.: Augmented secretion
Stimulation of sympathetic to salivary glands after parasympathetic stimulation leads to augmented secretion due
to active squeeze of acini as a result of sympathetic stimulation of myoepithelial cells surrounding acini (which are
filled with secretions by parasympathetic stimulation).
(III) Cooperative functions: (During sexual intercourse)
* Contraction of vas deference, seminal vesicle, * Secretory to seminal vesicle and prostate.
ejaculatory duct; producing ejaculation of
semen.
* Erection of penis and clitoris due to
* Shrinkage of penis and clitoris due to
vasodilatation.
vasoconstriction