Human Form & Function 1
NMS Systems
Lecture 13
Introduction to the
Autonomic Nervous System
Dr. Neil Docherty
My Teaching Objectives
•  To define the two autonomic branches of the efferent
arm of the peripheral nervous system
•  To revise the similarities and differences in the
structure of autonomic fibres according to the “twochain” hypothesis.
•  To systematically introduce the autonomic
neurotransmitters, their receptors, modes of signal
transmission and agonism/antagonism
•  To describe the concept of autonomic tone and
dominance with a focus on the myocardium
Efferent Branches of The
Peripheral Nervous System
•
Communication link between afferent visceral/sensory input to CNS
integration and effector function
afferent visceral/sensory input
C.N.S.
Electrical conduction/Chemical transmission
(neurotransmission)
Autonomic Nervous System
(A.N.S.)
Somatic Nervous System
(S.N.S.)
Effector function
USUALLY SUBCONSCIOUS
AND INVOLUNTARY
• Motility Related (Cardiac muscle and smooth muscle)
• Secretory (glands)
• Metabolic (liver and adipose tissue)
OFTEN CONSCIOUS AND
VOLUNTARY
• Skeletal muscle
Summary of A.N.S. Organisation
THORACOLUMBAR
(SYMPATHETIC)
CRANIOSACRAL
(PARASYMPATHETIC)
Adapted from Figure 7-2
Human Physiology Cells to Systems (7th Ed.) Sherwood L. p234
A.N.S. Efferent Pathways Are Formed
by a Two Neuron Chain
Direction of impulse
Multiple inputs
Multiple outputs
(varicosities)
Adapted from Figure 7-1 Human Physiology Cells to Systems (7th Ed.) Sherwood L. p234
C.N.S. Control Centres for A.N.S.
•  Spinal cord level
-autonomic reflexes (urination, defecation)
•  Brain Stem
-Medulla Oblongata
-cardiovascular, respiratory and digestive centres
•  Hypothalamus
-Superordinate to medulla in emotional and behavioural
responses
•  Pre-frontal Association Cortex
-Superordinate to autonomic manifestations of
emotional expression (e.g. blushing)
Summary
Branches of the A.N.S.
ORIGIN
STRUCTURE
GANGLIA
LOCATION
Sympathetic
Parasympathetic
Thoracic/Lumbar
Craniosacral
Short pre-ganglionic
Long pre-ganglionic
Long post-ganglionic
Short post-ganglionic
Paravertebral
Collateral
Terminal
(at or very near
organ)
The Autonomic Neurotransmitters
Chemical signals required to integrate a
multitude of finally tuned responses
However, only two main neurotransmittors
ACETYLCHOLINE (ACh)
NORADRENALINE
KEY CONCEPT
This makes us think that the diversity of responses is a
function of the way the signal is received
• Tissue specialisation
• Receptor effects
• Potential for pharmacological modulation of responses by
interfering with receptor activation
A.N.S. Neurotransmitters
PRE-GANGLIONIC
ACh in both branches
POST-GANGLIONIC
1. Sympathetic
•  Primarily noradrenaline
(Adrenergic fibres)
2. Parasympathetic
•  Primarily ACh
(Cholinergic fibres)
The Adrenal Medulla
-A Modified Sympathetic Ganglion
•
The adrenal gland is part of the endocrine system
•
Sympathetic pre-ganglionic fibres directly
stimulate the adrenal medulla (neuroendocrine
chromaffin cells)
•
Chromaffin cells synthesise adrenaline from
tyrosine in response to stimulation
•
N.B.adrenaline gives rise to similar effects
to noradrenaline except via the bloodstream
Signal Transmission-1
Adrenergic Receptor Subtypes
Alpha and Beta subtypes
Alpha-Two classes ( α1/ α2)
-Bind NA>A
- α1 Calcium second messenger EXCITATORY
e.g. peripheral vasoconstriction
- α2 Blockade of cAMP second messenger INHIBITORY
e.g. decreased digestive tract activity
Beta-Two classes ( β1/ β2)
- β1 NA + A equal affinity β2 primarily A
-cAMP second messenger system
- β1-Principally cardiac
e.g. increases rate and force of contraction
- β2-Primarily inhibitory
e.g bronchiolar dilatation
Adrenergic Receptor Signal Transmission
ALPHA 1
BETA
Three types (A,B,D)
All Increase PKC and Ca2+
2 types (1 and 2)
-β1-increase Ca2+
Increase heart rate and force
Increase smooth muscle contraction
ARTERIOLAE
ALPHA 2
3 types (A,B,C)
All Decrease cAMP and Ca2+
Decrease secretory activity
GI TRACT ENDOCRINE AND
EXOCRINE GLANDS
-β2-decrease Ca2+
Smooth muscle relaxation
e.g. bronchiolar dilatation
Signal Transmission 1
Cholinergic Receptor Subtyes
Nicotinic (N)
•  All autonomic ganglia
•  Binding stimulates inward cation flow in postganglionic
cell (ionotropic)
•  Muscarinic (M)
•  On effector cell membranes innervated by parasympathetic
branch
•  G protein, second messenger system linked.
•  Five classes (M1 to M5)
•  Divergent effects e.g. relaxation of cardiac muscle and
contraction of smooth muscle
Nicotinic and Muscarinic Receptor
Signal Transmission
NICOTINIC
MUSCARINIC
http://www.atsdr.cdc.gov/csem/cholinesterase/images/muscarinic_receptor.png
Dual A.N.S. Innervation
GENERAL RULE
Sympathetic and
parasympathetic usually
have directly opposing
effects on function
e.g heart rate, contractility)
Adapted from Figure 7-3
Human Physiology Cells to Systems (7th Ed.) Sherwood L. p234
Exceptions to Dual Innervation Effect Rule
•  Resistance vessels (arteriolae) receive only direct
sympathetic input.
(penis and clitoris excepted)
•  Sweat glands receive sympathetic cholinergic input
•  Salivary gland secretion increased by both sympathetic and
parasympathetic (qualitative differences in resultant saliva
due to balance of inputs)
Autonomic Tone
•  Partial activity of both branches exerts a
tonic effect on target organs
•  Can give way to dominance
(one up-one down shift in action potential frequency)
•  Can occur at single organ level in response to
detection of a change in set-points interpreted by
integrating centres-HOMEOSTATIC CONTROL
•  Large scale widespread activation more common in
sympathetic branch (e.g fight or flight)
Sympathetic Dominance
The Fight or Flight Response
A “Tour de Force” in Sympathetic Dominance
• In response to emergency/stressful situations the body must
prepare for a potential threat to be faced
PARAMETER
REQUIRMENT SYMPATHETIC EFFECT
Parasympathetic dominance
“Rest and Digest”
Nocturnal Dip
(heart rate variability)
Post-prandial dip
( parasympathetic branch
dominant in digestion and
Absorption)
M2 Cholinergic Receptors in the
Myocardium
Contrast the detail here with
that mentioned before regarding
adrenergic input in
the myocardium
The details reveals the physiological
explanantion for the inhibitory effects of
the parasympathetic branch on the
heart.
This is a good example of mutual
antagonism in A.N.S. function
SYMPATHETIC
EFFECT
PARASYMPATHETIC
EFFECT
Autonomic Agonists and Antagonists
1. Atropine
Effect-Selective antagonist of ACh at muscarinic receptors
Indication-Suppression of salivary and bronchial secretion during
surgery
2. Atenelol
Effect-Cardioselective β-adrenergic receptor antagonist (β1)
Indication-Hypertension,angina, tachyarrhythmias
3. Salbutamol
Effect-Selective activation of the β2 adrenergic receptor
Indication-Bronchiolar dilatation in asthma
On the Next Slide
Your Physiology Focused
A.N.S. Wallchart!
Your Learning from Today
Should focus on being able to
•  Describe the organisation and chemistry of the two
branches of the A.N.S.
•  Explain the key concepts of dual innervation,
antagonism, autonomic tone and dominance
•  Exemplify the multi-functionality of the A.N.S. with
reference to the “fight or flight” response