Transcript Autonomic nervous system

Autonomic nervous
system
By
Pak Int’l Med College
Peshawar::::
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The Autonomic nervous system is the portion of the nervous
system that controls most visceral functions of the body
It is primarily concerned with the regulation of visceral or
vegetative functions of the body, so it is called vegetative or
involuntary nervous system
This system helps to control arterial pressure, gastrointestinal
motility, sweating, body temperature and many other
activities some of which are controlled almost entirely and
some only particularly by the autonomic nervous system.
One of the most striking characteristic of the autonomic
nervous system is the rapidity and intensity with which it
can change visceral functions.
General organization of autonomic nervous
system.
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The autonomic nervous system is activated mainly by
centers located in the spinal cord, brainstem and
hypothalamus. Also portions of the cerebral cortex
especially of the limbic cortex, can transmit signal to
the lower centers and in this way influence autonomic
controls.
The autonomic nervous system also often operates
through visceral reflexes.
Division of ANS
From anatomical and physiological point of view, the
autonomic nervous system is divided into two divisions.
1.Sympathetic division
2. Parasympathetic division.
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It is otherwise called thoracolumber
outflow because the preganglionic
neurons are situated in lateral gray
horns of 12 thoracic and first two
lumber segments of spinal cord. The
fibers arising from here are known as
preganglionic fibers. The preganglionic
fibers leave the spinal cord through
anterior nerve root and white rami
communicants and terminates in the
postganglionic neurons, which are
situated in the sympathetic ganglia.
Sympathetic division supplies smooth
muscles fibers of all the visceral organs
such as blood vessels, heart, lungs,
glands, GIT etc
Sympathetic ganglia
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The ganglia of sympathetic
division are classified into
three groups.
1. Paravertebral or
sympathetic chain ganglia
2. Prevertebral or collateral
ganglia
3. Terminal or peripheral
ganglia
Paravertebral or sympathetic chain ganglia
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Paravertebral or sympathetic chain ganglia are arranged in a segmental
fashion along the anterolateral surface of vertebral column.
The ganglia on either side of the spinal cord are connected with each
other by longitudinal fibers to form the sympathetic chains.
Both the chains extend from skull to coccyx
Ganglia of the sympathetic chain (trunk) on each side are divided into
four groups.
1. Cervical ganglia.
2. Thoracic ganglia.
3. Lumber ganglia.
4. Sacral ganglia.
Prevertebral or collateral ganglia
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Prevertebral ganglia are situated in thorax, abdomen and
pelvis in relation to aorta and its branches
The Prevertebral ganglia are
1. Celiac ganglion
2. Superior mesenteric ganglion
3. Inferior mesenteric ganglion
The Prevertebral ganglia receives preganglionic fibers from T5
to L2 segments.
The postganglionic fibers from these ganglia supply the
visceral organs of thorax, abdomen and pelvis.
Terminal or peripheral ganglia.
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Terminal ganglia are situated within or close to
structures innervated by them.
Heart, bronchi, pancreas and urinary bladder are
innervated by the terminal ganglia
Segmental distribution of the SNF
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The sympathetic fiber from
cord segment are from
T1 generally passes up the
chain to the head
T2 in the neck
T3 ,T4 ,T5 and T6 into the
thorax
T7 ,T8 ,T9 ,T10 and T11
into the abdomen
T12 ,L1 ,L2 into the legs.
Sympathoadrenergic system
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Sympathoadrenergic system is a functional
phylogenetics unit that includes sympathetic division
and adrenal medulla
Adrenal medulla is a modified sympathetic ganglion.
Since adrenal medulla and sympathetic division
develop from same neural crest, their secretion and
functions are almost the same
Any increase in sympathetic activity increases the
secretion of Catecholamine from adrenal medulla
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The parasympathetic division of ANS
is otherwise called craniosacral
outflow because, the fibers of this
division arise from brain and sacral
segments of spinal cord.
The cranial portion of
parasympathetic division in
brainstem innervates the blood
vessels of the head and neck and
many thoracoabdominal visceral
organs.
The sacral portion in sacral segments
of the spinal cord innervates the
smooth muscles forming the walls of
viscera and the glands such as large
intestines, liver, spleen, kidneys,
bladder, genitalia etc
Cranial nerves of Parasympathetic division
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The cranial nerve of the parasympathetic division are.
1. Oculomotor (iii) nerve
2. Facial (vii) nerve
3. Glossopharyngeal (ix) nerve
4. Vagus (x) nerve
The fibers of sacral outflow arise from second to fourth sacral (s1 to s2 ) segments of
spinal cord and occasionally the first and fourth sacral nerves
Thus the preganglionic fibers of parasympathetic division arise from the neurons
situated at three different levels
1. Tectal or midbrain level (iii cranial nerve)
2. Bulbar level or bulbar outflow (vii, ix, x cranial nerve)
3. Sacral outflow (sacral nerves)
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Tectal or midbrain level.
In ciliary's ganglion
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Bulbar level or bulbar outflow.
Fibers of vii cranial nerve supply the lacrimal, nasal, sub maxillary and
sublingual glands
Fibers of ix cranial nerve supply the parotid gland
Fibers of x cranial nerve supply visceral organs of the body
 About 75 % of all parasympathetic nerve fibers are in Vagus
nerves passing entire thoracic and abdominal regions of the
body
Sacral outflow
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The preganglionic fibers arise from anterior gray horn
cells of 2nd, 3rd and 4th sacral segments of spinal cord
and form the pelvic nerve.
The fibers end on the postganglionic neurons which
are situated on or near the visceral organs.
The sacral parasympathetic fibers supply those
visceral organs which are not supplied by Vagus.
Neurotransmitter of ANS
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The different nerve fibers of ANS execute the functions by
releasing some neurotransmitter substance
Neurotransmitter substance
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Those fibers that secrete acetylcholine are said to be
cholinergic.
Those that secrete nor epinephrine are said to be
adrenergic, a term derived from adrenaline, which is
an alternate name for epinephrine
Sympathetic fibers
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Preganglionic fibers: Acetylcholine (ach)
Postganglionic noradrenergic fibers: Nor adrenaline
Postganglionic cholinergic fibers: Ach
The postganglionic sympathetic cholinergic nerve
fibers supply sweat gland and blood vessels in heart
and in skeletal muscle.
Parasympathetic fibers
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Preganglionic fibers: ACH
Postganglionic fibers: ACH
Types of acetylcholine receptors
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Acetylcholine activates mainly two types of receptors.
They are called
Muscarinic and nicotinic receptors.
The reason for these names is that muscarine, a poison
from toadstools, activates only Muscarinic receptors
and will not activate nicotinic receptor, whereas
nicotine activates only nicotinic receptor
;Acetylcholine activates both of them
Adrenergic receptors.
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These are also two major types of adrenergic receptors,
ALPHA and BETA receptors.
Alpha: alpha1 and alpha2
Beta: beta1 beta2 and beta3
Adrenergic receptors and function
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ALPHA
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Vasoconstriction
Iris dilation
Intestinal relaxation
Intestinal sphincter
contraction
Pilomotor contraction
Bladder sphincter
contraction
Inhibits neurotransmitter
release
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BETA
Vasodilatation
Cardioacceleration
Increased myocardial
strength
Intestinal relaxation
Bronchodilator
Calorigenesis
Glycogenolysis