Transcript Lecture6 - Part 1 ANS student (2012).

Autonomic Nervous System ( ANS)
Part 1
Dr Taha Sadig Ahmed
Physiology Department , College of Medicine ,
King Saud University , Riyadh
Nervous System
(I) Central Nervous System
(II) Peripheral Nervous
System
(I) Central Nervous System (CNS)
Consists of Brain & Spinal Cord
Brain
(1)Forebrain: Cerebrum, Diencephalon (Thalamus, Metathalamus,
Epithalamus, Hypothalamus and subthalamus
(2)Mid brain
(3) Hind brain: Pons, Medulla , Cerebellum
B/Spinal cord
• (II) Peripheral Nervous System:
 Consists of cranial nerves (arising from brain) and spinal nerves
(arising from spinal cord)
 The Nervous System can also be classified into :
(I) Somatic ( voluntary) Nervous System : For organs
•
under voluntary control (namely skeletal muscles)
(II) Autonomic (involuntary,visceral) Nervous System:
•
Not under voluntary control.
•
It regulates internal organs’ visceral functions and homeostasis
•
Effectors include cardiac muscles , smooth muscles and glands
•
The Autonomic Nervous System ( ANS) helps to adjust &
maintain the internal environment ( homeostasis); and helps the
body to adapt to to changes in the external environment ,
ANS is controlled
activated by centers
located in the spinal
cord, brain stem,
hypothalamus and also
cerebral cortex
especially the limbic
cortex
 The hypothalamus is
very important in this
regard :
Posterior
hypothalamus controls
Sympathetic NS , &
Anterior hypothalamus
controls
Parasympathetic NS
Parasympathetic NS
Sympathetic NS
• Parasympathetic system activities is related to the relaxed state , rest and
anabolism 
• It promotes vegetative functions ( nutritive , body-building , restorative functions
& tissue repair )
• Increased secretion of endocrine & exocrine glands .
5
COMPARISON OF AUTONOMIC AND SOMATIC
SYSTEMS
Somatic system
– One motor neuron extends from the CNS to
skeletal muscle
– Axons are well myelinated
– Conduct impulses rapidly
THE AUTONOMIC NERVOUS SYSTEM
Sympathetic
and
parasympathetic
systems
are
consists of myelinated pre-ganglionic fibers which
make
synaptic
connections
with
un-myelinated
postganglionic fibers and then innervate the effector
organ
These synapses usually occur in clusters called ganglia.
COMPARISON OF AUTONOMIC AND SOMATIC MOTOR
SYSTEMS
Autonomic nervous system
– Chain of two motor neurons in series
• Preganglionic neuron ( have myelinated axons)
• Postganglionic neuron ( have unmyelinated , thin axons )
– Conduction is slower than in Somatic due to
presence of thin , un-myelinated postganglionic
axons
Pre-ganglionic
Post-ganglionic
Ganglion
The Autonomic Outflow consists 2 Neurons neurons
arranged in series:
• (A) Preganglionic nerves:
(1) Are myelinated
(2) In case of sympathetic NS 
arise from spinal cord
In case of Parasympathetic NS
 arise from Brainstem + spinal
cord
•.(B) Postganglionic nerves : arise
from ganglia .
(1) Are unmywelinated
(2) arise from ganglia .
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COMPARISON OF AUTONOMIC AND SOMATIC
MOTOR SYSTEMS
THE AUTONOMIC NERVOUS SYSTEM
2 neurons in the efferent
pathway.
1st neuron has its cell body
in gray matter of brain
or spinal cord.
Preganglionic neuron.
• Synapses with 2nd
neuron within an
autonomic ganglion.
Postganglionic neuron.
• Autonomic ganglion has
axon which extends to
synapse with target
tissue.
THE AUTONOMIC NERVOUS SYSTEM
Sympathetic
and
parasympathetic
systems
are
consists of myelinated pre-ganglionic fibers which
make
synaptic
connections
with
un-myelinated
postganglionic fibers and then innervate the effector
organ
These synapses usually occur in clusters called ganglia.
Preganglionic neuron:
 Cell body in brain or spinal cord
 Axon is myelinated type fiber that extends to
autonomic ganglion
Postganglionic neuron:
 Cell body lies outside the CNS in an autonomic
ganglion
 Axon is unmyelinated type fiber that terminates
in a visceral effector
DIFFERENCES IN SYMPATHETIC AND
PARASYMPATHETIC DIVISIONS
• Length of postganglionic fibers
– Sympathetic  long postganglionic fibers
– Parasympathetic  short postganglionic fibers
– Therefore , in sympathetic Preganglionic fibers
are shorter than Postganglionic ones
– And in parasympathetic Preganglionic fibers
are longer than Postganglionic ones .
• Branching of axons
– Sympathetic axons – highly branched
– Parasympathetic axons – few branches
DIFFERENCES IN SYMPATHETIC AND
PARASYMPATHETIC DIVISIONS
Subdivision
of ANS
Location of
soma ( cellbody ) of
preganglionic
nerve
Sympathetic
Thoracolumbar Alongside
Segments of
vertebral
spinal cord
column ;
ACh is
transmitter
Parasympath
etic
Cranium ( in
side skull , in
Brain ) and
Sacral
Segments of
Spinal Cord
Location of
Ganglia &
Transmitter
at Ganglia
Chemical
secreted by
Postganglionic
Fiber
General
Function
Norepinephrine; Fight or
except
flight
(1) Vasodilator
postganglionic
sympathetic
fibers in
Skeletal Muscle
(2) Postganglionic
sympathetic
fibers to Sweat
Glands
On or near
Acetylcholine
the effector
organ; ACh is
transmitter
Conservation
of body
energy
 Preganglionic Sympathetic nerves
exit the CNS from the thoracic + lumbar
segments of the spinal cord
Therefore , the sympathetic system is
also called : “ Thoraco-lumbar Outflow “
 Preganglionic Parasympathetic nerves
exit the CNS from the Cranium ( skull ) +sacral
segments of the spinal cord
Therefore , the Parasympathetic system
is called : “ Craniosacral Outflow “
 Hence , in the Sympathtic system ,
Preganglionic fibers are myelinated and
shorter than the unmyelinated Postganglionic
fibers
 In Parasympathetic system , Preganglionic
fibers are also myelinated but longer than the
unmyelinated Postganglionic fibers .
Origin of ANS fibers
Sympathetic: Originate in the thoracic and lumbar
regions of the spinal cord (Thoracolumbar)
Parasympathetic: Originate from cranial nerves (3rd,
7th, 9th, 10th), and sacral spinal nerves (craniosacral)
 In the Parasympathetic NS , there is little
divergence  the ratio of pre- to postgaglionic
fibers is 1/3 .
 This little divergence implies more specific ,
localized actions .
 On the other hand , in the Sympathetic NS
there is greater divergence . The ratio
(pre/post) being = 1/10 ;
 This divergence implies diffuse ( generalized )
actions .
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THE AUTONOMIC NERVOUS SYSTEM