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Autonomic Response ?
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Autonomic Nervous System
Part of the Nervous system that Controls
most of the Visceral Functions of the
Body ( Automatically ? )
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Classification Of CNS
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Autonomic Nervous System
• Visceral functions
– Heart and Blood Pressure
– GIT motility & Secretions
– Urinary Bladder emptying
– Sweating & Body Temperature regulation
– Bronchodilation and Constriction
– Muscle Blood flow
• Rapidity & Intensity – Functions within
seconds
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Autonomic Nervous System
• Higher control:
– Spinal cord
– Brain Stem
– Hypothalamus
– Limbic System
• Visceral Reflexes- Subconscious Reflex
Response
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Typical Spinal Nerve
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Peshawar Medical College NWFP Pakistan
Peshawar Medical College NWFP Pakistan
Physiologic Anatomy of the
Sympathetic Nervous System
Paravertebral sympathetic chains of ganglia
• Prevertebral ganglia (collateral ganglia)
are sympathetic ganglia which lie between
the paravertebral ganglia and the target
organ.
• Nerves extending from the ganglia to the
different internal organs.
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• The sympathetic nerve fibers originate in
the spinal cord along with spinal nerves
between cord segments T-1 and L-2 and
pass first into the sympathetic chain and
then to the tissues and organs that are
stimulated by the sympathetic nerves.
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Peshawar Medical College NWFP Pakistan
• The cell body of each preganglionic
neuron lies in the intermediolateral horn of
the spinal cord; its fiber passes,through an
anterior root of the cord into the
corresponding spinal nerve.
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• Immediately after the spinal nerve leaves the
spinal canal, the preganglionic sympathetic
fibers leave the spinal nerve and pass through a
white ramus into one of the ganglia of the
sympathetic chain.
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• Then the course of the fibers can be one
of the following three:
• (1) It can synapse with postganglionic
sympathetic neurons in the ganglion that it
enters.
• (2) it can pass upward or downward in the
chain and synapse in one of the other
ganglia of the chain.
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• (3) it can pass for variable distances
through the chain and then through one of
the sympathetic nerves radiating outward
from the chain, finally synapsing in a
peripheral sympathetic ganglion.
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• The postganglionic sympathetic neuron
thus originates either in one of the
sympathetic chain ganglia or in one of the
peripheral sympathetic ganglia.
• From either of these two sources, the
postganglionic fibers then travel to their
destinations in the various organs.
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• The splanchnic nerves are paired
visceral nerves (nerves that contribute to the
innervation of the internal organs), carrying
fibers of the autonomic nervous system (visceral
efferent fibers) as well as sensory fibers from the
organs (visceral afferent fibers).
• Thoracic splanchnic nerves are splanchnic
nerves that arise from the sympathetic trunk
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Peshawar Medical College NWFP Pakistan
Sympathetic Nerve Fibers in
the Skeletal Nerves.
• Some of the postganglionic fibers pass
back from the sympathetic chain into the
spinal nerves through gray rami at all
levels of the cord.
• These sympathetic fibers are all very
small type C fibers, and they extend to all
parts of the body by way of the skeletal
nerves.
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• They control the blood vessels, sweat
glands, and piloerector muscles of the
hairs.
• About 8 per cent of the fibers in the
average skeletal nerve are sympathetic
fibers.
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Peshawar Medical College NWFP Pakistan
Peshawar Medical College NWFP Pakistan
Segmental Distribution of the
Sympathetic Nerve Fibers.
The sympathetic fibers from cord segment:
 T-1 pass up the sympathetic chain to
terminate in the head;
 T-2 to terminate in the neck;
 T-3, T-4, T-5, and T-6 into the thorax;
 T-7, T-8, T-9, T-10 &T-11 into the
abdomen;
 T-12, L-1 & L-2 into the legs.
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Special Nature of the Sympathetic
Nerve Endings in the Adrenal Medullae.
Preganglionic sympathetic nerve fibers pass,
without synapsing, all the way from the
intermediolateral horn cells of the spinal cord,
through the sympathetic, then through the
splanchnic nerves, and finally into the two
adrenal medullae.
 There they end directly on modified neuronal
cells that secrete epinephrine and
norepinephrine into the blood stream.
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Physiologic Anatomy of the
Parasympathetic Nervous System
• Parasympathetic fibers leave the central
nervous system through:
• cranial nerves III(Oculomotor),
• VII( Facial), IX(Glossophyrangeal),
• and X( Vagus);
• Additional parasympathetic fibers leave the
lowermost part of the spinal cord through the
S2 & S3 sacral spinal nerves.
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• About 75 per cent of all parasympathetic
nerve fibers are in the vagus nerves
(cranial nerve X), passing to the entire
thoracic and abdominal regions of the
body.
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Peshawar Medical College NWFP Pakistan
• The vagus nerves supply parasympathetic
nerves to the
• Heart,
• Lungs,
• Esophagus,
• Stomach,
• Entire small intestine,
• Proximal half of the colon,
• Liver, Gallbladder, Pancreas, Kidneys, and
• Upper portions of the ureters.
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• Parasympathetic fibers in III cranial nerve
go to the pupillary sphincter and ciliary
muscle of the eye.
• Fibers from VII cranial nerve pass to the
lacrimal, nasal, and submandibular glands.
Fibers from IX cranial nerve go to the
parotid gland.
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• Sacral parasympathetic fibers are in the
pelvic nerves, which pass through the
spinal nerve sacral plexus on each side of
the cord at the S-2 and S-3 levels.
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•
•
•
•
•
•
These fibers then distribute to the:
Descending colon,
Rectum,
Urinary bladder, and
Lower portions of the ureters.
This sacral group of parasympathetics
supplies nerve signals to the external
genitalia to cause erection.
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Preganglionic and Postganglionic
Parasympathetic Neurons
• The parasympathetic system, like the
sympathetic, has both preganglionic and
postganglionic neurons.
• The preganglionic fibers pass
uninterrupted all the way to the organ that
is to be controlled.
• .
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• In the wall of the organ are located the
postganglionic neurons.
• The preganglionic fibers synapse with
very, very short postganglionic fibers, a
fraction of a millimeter to several
centimeters in length.
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Parasympathetic
Division
Cranial Nerves
III - Occulomotor N
VII- Facial N
IX - Glossopharyngeal N
X - Vagus N
Sacral Outflow:
S1 – S4
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Basic Characteristics
Cholinergic & Adrenergic Fibers
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Peshawar Medical College NWFP Pakistan
• The sympathetic and parasympathetic nerve
fibers secrete mainly one or the other of two
synaptic transmitter substances, acetylcholine
or norepinephrine.
• Those fibers that secrete acetylcholine are
said to be cholinergic.
• Those that secrete norepinephrine are said to
be adrenergic, a term derived from adrenalin,
which is an alternate name for epinephrine.
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Sympathetic
Cholinergic
Parasympathetic
Cholinergic
Cholinergic
Sweat Glands, Piloerector Muscle,
A few Blood Vessels
Adrenergic
Cholinergic
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Acetylcholine is called a parasympathetic
transmitter.
Norepinephrine is called a sympathetic
transmitter.
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Peshawar Medical College NWFP Pakistan
Other Neurotransmitters
• Dopamine
• GnRH (Gonadotrophin Releasing
Hormone)
• Co-transmitters
– VIP
– Neuropeptide Y
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Mechanisms of Transmitter Secretion
and Removal at Postganglionic Endings:
Secretion of Acetylcholine and
Norepinephrine by Postganglionic Nerve
Endings
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• many of the parasympathetic nerve fibers
and almost all the sympathetic fibers
merely touch the effector cells of the
organs
• Where these filaments touch or pass over
or near the cells to be stimulated, they
usually have bulbous enlargements called
varicosities
• Here Neurotransmitters are synthesized
and stored
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Release of autonomic
neurotransmitters in Smooth Muscle
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• varicosities have large numbers of
mitochondria that supply adenosine
triphosphate, which is required to energize
acetylcholine or norepinephrine synthesis.
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 An action potential spreads over the
terminal fibers--- the depolarization
process increases the permeability of the
fiber membrane to calcium ions---allowing
these ions to diffuse into the nerve
terminals or nerve varicosities.
 The calcium ions -- cause the terminals or
varicosities to empty their contents to the
exterior.
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• Acetyl-CoA + Choline
choline acetyle
transferase
Acetyl choline
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• Once acetylcholine is secreted into a
tissue by a cholinergic nerve ending, it
persists in the tissue for a few seconds
while it performs its nerve signal
transmitter function.
• Then it is split into an acetate ion and
choline, catalyzed by the enzyme
acetylcholinesterase that is bound with
collagen
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Synthesis & Release of Acetylcholine
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Removal of norepinephrine:
• reuptake into the adrenergic nerve
endings by an active transport process, --removal of 50 to 80 percent of the
secreted norepinephrine;
• diffusion away from the nerve endings
into the surrounding body fluids and then
into the blood
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• destruction of small amounts by tissue
enzymes -- monoamine oxidase, which is
found in the nerve endings,
• catechol-O-methyl transferase-- in the
tissues
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Metabolism of Neurotransmitters
• Acetylcholine
– Synthesis
•
Norepinephrine
–
• From Choline
• In terminal nerve
endings
– Destruction (enzyme)
• Acetylcholinesterase
Synthesis
•
•
–
From Tyrosine
In axoplasm of nerve
endings
Removal
i. Reuptake
ii. Blood
iii. Enzymes (MAO)&
catechol-O-methyl
transferase,
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Circulation of neurotransmitters
• Acetylcholine:
– Local
• Noradrenaline/ Norepinephrine:
– Local
– Blood
• Adrenaline/ Epinephrine
– Blood
– Hormone
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• RECEPTORS ON THE EFFECTOR
ORGANS
• acetylcholine, norepinephrine, or
epinephrine bind with specific receptors
on the effector cells.
• The receptor is on the outside of the cell
membrane ( penetrates all the way
through the cell membrane)
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• Conformational change in the structure of
the protein molecule-- altered protein
molecule excites or inhibits the cell by
(1) causing a change in cell membrane
permeability to one or more ions or
(2) activating or inactivating an enzyme
attached to the other end of the receptor –
increases the activity of the enzyme
adenylyl cyclase on the inside of the cell,
which causes formation of cyclic adenosine
monophosphate (cAMP).
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Autonomic Receptors
Receptors
Cholinergic
Muscarinic
Adrenergic
Nicotinic
Alpha 1
Beta
Alpha
Alpha 2
Beta 1
Beta 2
Beta 3
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Amanita muscaria, the mushroom from which
muscarine was isolated
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• Muscarinic receptors are found on all
effector cells that are stimulated by the
postganglionic cholinergic neurons of
either the parasympathetic nervous
system or the sympathetic system.
• Muscarinic receptors use G proteins as
their signaling mechanism
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• Nicotinic receptors (ligand-gated ion
channels) are found in the autonomic
ganglia at the synapses between the
preganglionic and postganglionic neurons
of both the sympathetic and
parasympathetic systems.
– Also found at NMJ in Skeletal Muscles.
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Adrenergic Receptors—Alpha and Beta
Receptors
• use G proteins for signaling.
• Norepinephrine excites mainly alpha receptors
but excites the beta receptors to a lesser extent
as well.
• Epinephrine excites both types of receptors
• relative effects are determined by the types of
receptors in the organs. If they are all beta
receptors, epinephrine will be the more effective
excitant.
•
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• alpha and beta receptors are not
necessarily associated with excitation or
inhibition but with the affinity of the
hormone for the receptors in the given
effector organ.
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Peshawar Medical College NWFP Pakistan
Organs Receiving only Sympathetic
Innervation
• Adrenal Medulla
• Kidney
• Piloerrector muscles (Cholinergic)
• Sweat glands (Cholinergic)
• Vessels
• Metabolic processes
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General Rule:
Function of the autonomic nerves is
dependent on
the type of receptor
present on the postsynaptic
membrane
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Sympathetic functions
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Parasympathetic functions
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Autonomic functions
Organ
Parasympathetic
Sympathetic
EYE
1.
2.
Miosis(constricted pupils)
Near Accommodation
(cilliary muscles
constricted)
1.
2.
HEART
1.
2.
3.
↓ Heart rate
↓ force of contraction
↓ Conduction of velocity
Opposite
(ß-1 receptors)
BLOOD
VESSELS
1.
Dilation ?
1.
Mydriasis
Opposite
Alpha receptors:
Constriction
2. ß-2 receptors :
Dilatation e.g.
Coronary
arteries, skeletal
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Organ
Parasympathetic
Lungs
1.
2.
GIT
Stomach, Intestine
1. ↑ Motility
2. ↑ Secretions
3. Sphincters relaxed
Gall Bladder/Ducts:
Contraction
Opposite
URINARY
BLADDER
1.
Opposite
MTABOLISM
Muscle contraction
↑ secretion
2.
Detrusor Muscle
Contraction
Sphincter relaxed
1.
Anabolism
Sympathetic
Opposite(ß-2)
Catabolism (ß
receptors)
•
↑ glycogenolysis
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Organ
Parasympathetic Sympathetic
Kidney
Nil
Mental
activity
Nil
Skeletal
Muscle
Nil
Reduce output
and Increase
Renin
Secretion
↑
↑ Glycogenolysis
↑ Strength
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Autonomic Functions
• Opposite to each other
– Excitatory / Inhibitory
• Parasympathetic:
– Localized
• Sympathetic:
– Diffuse
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Physiological Differences B/W
Adrenaline & Nor-Adrenaline
Adrenalin (Epinephrine).
Nor-adrenalin(Nor-Epi)
1. Greater effect on beta
Receptors-Greater
efffect on Heart.
2. Weak vasoconstrictor in
Muscles , hence rise in
TPR is less But
Increase more COP.
3. 5-10 time more effect on
tissue metabolism than
Nor-epinephrine
• 1.Less effect on Heart
stimulation
2. Strong Constriction in
Muscles, Hence increase
in TPR is more -> Rise in
BP
3. Less effect on tissue
metabloism
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