PHSL2101 - PHSL2121 – PHSL2501
Autonomic Nervous System
A/Prof Richard Vickery
Dept of Physiology
School of Medical Sciences, UNSW
Richard.Vickery@unsw.edu.au
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Learning Objectives for the ANS
►Outline the operation of reflex control in the
autonomic nervous system.
►Describe the anatomical organization of the
sympathetic and parasympathetic systems.
►List the neurotransmitters and receptor classes
used by the sympathetic & parasympathetic
systems at pre-ganglionic & post-ganglionic
synapses.
►List the effects of the autonomic nervous system
on the heart, lungs, and circulation.
Divisions of the nervous system
CNS ~1011 neurons
PNS ~108 neurons
from Brown & Benchmark Introductory Psychology Image Bank copyright 1995 Times Mirror Higher Education Group, Inc.
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ANS controls the four F's
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from cartoonspot.net & www.acartoonchristmas.com
The ANS, reflexes, and emotions
Non-conscious
processing of inputs
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The ANS is intimately involved with our emotions: in their
physical expression, and perhaps in their generation.
This also provides a path for conscious influence over the ANS.
from Levenson (2014) Emotion Review 6:100
Reflex loops control autonomic function
Sensory input leads to
autonomic effects at
local, and at higher,
more integrated, levels.
1. enteric nervous system
or effector organ
2. ganglion: integrate
sensory, preganglionic,
and interneurons
3. spinal cord: integrate
across spinal levels
4. brain stem: integrate
across organs
5. higher centres:
integrate with
motivation and desires
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from Medical Physiology by Boron and Boulpaep,
Saunders, Philadelphia, 2003
Many brain regions including brain stem,
are part of the autonomic nervous system
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These regions
integrate sensory
inputs from
diverse sources to
produce a
coordinated
output. They
usually influence
sympathetic and
parasympathetic
systems in
tandem.
from Germann and Stanfield, Benjamin Cummings, 2005
Roles of parasympathetic and
sympathetic systems
Parasympathetic - dominant at rest
Sympathetic - dominant for "fight or flight"
Enteric - autonomous 100 000 000 neurons
control gut motility and secretion
Parasympathetic and Sympathetic tend to work in
opposition like a brake and accelerator in a car.
Sympathetic and parasympathetic nerves also carry
sensory information: mainly pain sense in
sympathetic, and visceral senses such as distension
or blood chemistry in the parasympathetic.Re
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Reflex loops depend on sensory input
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Sensory input comes
mainly from autonomic/
visceral afferents.
1. These afferents are
mainly located in the
innervated tissue and
travel in the same nerve
as efferents.
2. Higher centres integrate
inputs from a broader
region.
3. Somatic inputs are
integrated to provide
fast or predictive
responses, like to
posture adjustment.
from Germann and Stanfield, Benjamin Cummings, 2005
Basic plan of the efferent autonomic
nervous system
from Medical Physiology by Boron and Boulpaep, Saunders, Philadelphia, 2003
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Anatomical organization of the ANS
fro
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G
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St
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fie
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, B
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, 2
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5
O
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The enteric nervous system is a complex
network of different neurons
A scanning electron
micrograph of the
myenteric plexus of the
mouse large intestine.
The plexus is the highly
interconnected
meshwork spreading
over the deeper circular
layer of muscle.
O
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from Medical Physiology by Boron and Boulpaep,
Saunders, Philadelphia, 2003
Three divisions of the sympathetic system
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Most sympathetic activity goes via the sympathetic chain, but
more specific effects can be via collateral ganglia, whereas
general effects can be produced by adrenaline released from
the adrenal medulla.
Parasympathetic works on basically a collateral ganglion model.
from Germann and Stanfield, Benjamin Cummings, 2005
Organization of the sympathetic chain
fro
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M
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P
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Sa
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, P
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2
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Autonomic synapses on target organ:
each neuron makes many synapses
(G. Burnstock G, J. Anat 146: 1-30, 1986)
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The autonomic system is like the skeletal muscle system. It has
axons that form synapses on the target tissue. Like the NMJ,
these axons often produce strong effects by acting at a lot of
release sites.
from Medical Physiology by Boron and Boulpaep,
Saunders, Philadelphia, 2003
Synaptic cleft may be wider than at
somatic synapses
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The autonomic synapse
works basically like the
NMJ. The space the
transmitter has to diffuse
is a bit greater; this may
allow more spill-over
effects.
from Germann and Stanfield, Benjamin Cummings, 2005
ANS uses specific neurotransmitters
Norepinephrine
is American for
Noradrenaline.
Epinephrine
is American for
Adrenaline.
Tr
an
sm
itt
er
s &
re
ce
pt
or
s
from Medical Physiology by Boron and
Boulpaep, Saunders, Philadelphia, 2003
Receptor classes for Acetylcholine
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The autonomic nervous system uses ionotropic receptors in the
ganglia, and then switches to metabotropic at the target
organ.
from Germann and Stanfield, Benjamin Cummings, 2005
Receptor classes for Noradrenaline
from Germann and Stanfield, Benjamin Cummings, 2005
Tr
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Multiple neurotransmitters are released
Synapses often release a variety of transmitters. These can
produce different effects, and my be somewhat selectable
based on the rate of axon activity. from Medical Physiology by Boron and
Boulpaep, Saunders, Philadelphia, 2003
Tr
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pt
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Autonomic control of organs - 1
Ef
fe
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s o
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A
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from Germann and Stanfield, Benjamin Cummings, 2005
Autonomic control of organs - 2
Ef
fe
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s o
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he
A
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from Germann and Stanfield, Benjamin Cummings, 2005
The ANS in action
Let's flesh out this reflex loop
we saw earlier....
Ef
fe
ct
s o
f t
he
A
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Baroreceptors are specialised
neurons that alter their activity
based on vessel stretch
The baroreceptors synapse on
brainstem cardiovascular centres
Increased sympathetic activity
restores blood pressure largely by
increasing peripheral vasoconstriction
Reduced parasympathetic
activity increases the rate of
heart contraction
from Germann and Stanfield, Benjamin Cummings, 2005