The Autonomic Nervous System
Learning Objectives
• To understand the classification of the NS on the basis of function
• To distinguish between the Somatic & Autonomic NS
• To understand the generic layout of the Autonomic NS in general
• To compare & contrast anatomical distributions of sympathetic vs
parasympathetic divisions of the Nervous System
The Neurone
Cell Body
• Also known as the nerve cell
• It is the minimal functional unit
of the Nervous System
• Its main features are:
• The Cell body (n=1)
• The Axon (n=1)
Cartoon
Classification of Nervous System Tissues
Overview of The Nervous System
The Nervous System
Anatomical
Central Nervous System Peripheral Nervous System
Classification
Direction of
Afferent System Efferent System Signalling
Somatic Nervous Autonomic
Afferents Functional
System Efferents Nervous System Efferents
The Nervous System
Overview of The Nervous System
The Nervous System
Anatomical
Central Nervous System Peripheral Nervous System
Classification
Direction of
Afferent System Efferent System Signalling
Somatic Nervous Autonomic
Afferents Functional
System Efferents Nervous System Efferents
The Nervous System
Overview of The Nervous System
The Nervous System
Anatomical
Central Nervous System Peripheral Nervous System
Classification
Direction of
Afferent System Efferent System Signalling
Somatic Nervous Autonomic Functional
System Efferents Nervous System Efferents
Afferents Somatic Efferents Sympathetic Parasympathetic Enteric
The Nervous System
The Autonomic Nervous System
About The Autonomic Nervous System
• Represents ‘ancient’ control • Becomes active along with
systems of the body organogenesis
• Subserves ‘fundamental’ life- • Functions non-stop throughout
functions life
– e.g. survival of individual,
– promotion of species • Controls function by changing
– care of offspring etc the continuous output in two
‘reciprocal’ systems
• Maintains a constant internal
environment in the body • Predominant Actions of the ANS
– Also known as homeostasis reflects an Imbalance in the
outputs of its two ‘reciprocal’
systems
General Actions of The ANS
• Constancy
• 1) Establishes & maintains Homeostasis of internal environment in the body
– through Regulation of various systems of the body:
• Cardiovascular
• Respiratory
• Digestive
• Thermo-regulative Apparatus
• Intermittent Change in Bias
• 2) Promotes Excretory mechanisms of the body as & when Necessary & Appropriate
Effector Organs of The ANS
• Divisible into 2 categories of tisssues of the body
• Muscles of the body that generate their own electrical activity
– Smooth Muscles
• Walls of blood vessels
• Tube of the GITract
– Cardiac Muscles
• Secretory Glands (Part of the Epithelia Group of Tissues)
Actions of Somatic vs Autonomic Divisions of Nervous System
Somatic Nervous System Autonomic Nervous System
• Under voluntary control • Not under voluntary control
• Pick a pen and scribble any • Double your heart rate
number you choose • Then halve the heart’s original
resting rate
• Use index finger to touch nose • Produce 10ml of sweat through
the left armpit only
• Tap your left foot once every • Dilate the right eye pupil to a
second, after 4 taps, pause for 1 diameter of 5mm
minute then resume the task etc.
Overview of ANS
Autonomic Nervous System
Sympathetic Parasympathetic
The Sympathetic & Parasympathetic Systems of the ANS
• Have a common standard anatomical layout
• Sympathetic & Parasympathetic systems differ in detail of
respective anatomy
• They each have an equal number of synapses in an in-
series arrangement
• The various synapses use different transmitters
• These differences form the basis for general
therapeutics
Overview of the Autonomic Nervous System
• General layout is very simple
CNS • True anatomical layout is complex
• There are always 2 neurones
arranged in-series for this pathway
• 1 cell has cell body in the CNS
PNS • 1 cell has cell body in the PNS
• Neurones exert actions via 3 classes
of effector organs
• This layout allows for a lot of
flexibility
General Layout of Autonomic Efferents
• Appears very simple
• 2 neurones in a chain
• 1 neurone in CNS (pre-ganglionic)
– does not supply effector organs directly
• 1 neurone wholly in PNS (post-ganglionic)
– relies on pre-ganglionic neurone for drive
– terminates directly on effector organ
• Multiple effector organs
– smooth muscle
– secretory glands
– cardiac muscle
Transmitters & Receptors of the ANS
• Knowledge of these will serve you well in the future
• They are the essence of therapeutics & its side-effects
• Some are more important than others e.g. cardiac ones
• Exceptions are very important
• This is probably the most dynamic area in medicine
(Pharmaceuticals)
General Design of Organisation of Autonomic of Outflow
CNS Nucleus Cell Body of Pre-ganglionic Neurone in CNS
Axon of Pre-
Ganglionic
Neurone
Terminals of Axon of Pre-ganglionic Neurone
Autonomic Ganglion Cell Body of Post-ganglionic Neurone in PNS
(Collections of Cell Bodies form Ganglia)
Axon of Post-
Ganglionic
Neurone
Terminals of Axon of Post-ganglionic Neurone
Effector Organ
General Structure of Outflow of Autonomic Signals
Parasympathetic Specific CNS Nuclei Sympathetic
Synthesises Synthesises
Acetylcholine & Acetylcholine &
Acts via Nicotinic Acts via Nicotinic
Receptors Receptors
In walls of effector Autonomic Form Paravertebral
organ or Near Ganglion Chain
Branches of CNV or Pre-vertebral
Ganglia
Synthesises Ach & Synthesises
acts via Muscarinic Noradrenaline
Receptors or Adrenaline & acts via
α- or β- Adrenoceptors
Effector Organ
Variations of Central Control of ANS
PARASYMPATHETIC SYMPATHETIC
Brain
High Structures
Brain Structures High Brain Structures
Brainstem/Spinal Cord Spinal Cord
Wall of Effector Organ Paravertebral Chain
Effector Organ Effector Organ
Autonomic Innervation of Organs
• Most organs are innervated by the ANS
• Most receive dual innervation of SNS &PNS
• Most effects of the SNS & PNS are reciprocal
• Autonomic tone varies between SNS & PNS dominance
• Predominant ANS tone is determined by the balance of outputs of
SNS & PNS
• Sweat glands receive sympathetic drive only
The Urinary Bladder As An Effector Organ
Overview of Autonomic Outflow
• Overview picture of
autonomic outflow from the
central nervous system is
complex
• There are obvious simple
patterns of distribution along
functional lines
• There is nothing simple about
distribution of these nerves
The Autonomic Nervous System
• Autonomic Fibres originate from:
• Cranio-sacral sources
• Parasympathetic in Function
• Somata found in
– Specific, named cranial nuclei
– &
– S2, 3 & 4 Segments of the Spinal Cord
• Axons of cranial nuclei reach periphery by hitch-
hiking on fibres of the following cranial nerves: III,
VII, IX and X
• Thoraco-lumbar Sources
• Sympathetic in Function
• All Neural Segments of spinal cord between T1 and
L2
mid brain
medulla
Parasympathetic
Cranio-sacral Sympathetic
Outflow
Thoraco-lumbar Outflow
General Structure of Outflow of Autonomic Signals
Parasympathetic Specific CNS Nuclei Sympathetic
Autonomic
Ganglion
Effector Organ
The Importance of understanding distribution of
autonomic outflow
• It is important that we are comfortable with
intricacies of distribution of autonomic outflow
• This knowledge is critical because autonomic
outflow is fragmented between sections of
the Central Nervous System
• Lesions of the CNS may lead to imbalances
of autonomic outflow to visceral organs
• Unbalanced autonomic outflow will lead to
disturbed autonomic reflexes.
• This can easily lead to death if not managed
expertly
GENERAL ORGANISATION OF
PARASYMPATHETIC OUTFLOW
Two Variants of Parasympathetic Outflow
• Distribution of Parasympathetic Outflow
can be generalised to that supplying:
• Visceral Organs of the Body
(excluding Head Region)
• or
• Head Region
PARASYMPATHETIC OUTFLOW TO
VISCERAL ORGANS (excl. The Head)
General Layout of Parasympathetic ANS
• Sources of Parasympathetic Autonomic
Outflow To Viscera
• Cranial Nerve Source:
• Specific Cranial Nuclei
• These include vagal nuclei
• Axons travel as part of CNX
• Spinal Cord Source
• S2-S4
Parasympathetic Output Via the Vagus Nerve or S2-S4
Segmental Nerves
• Pre-ganglionic neurones are found in either:
– Dorsal vagal motor nucleus
– Or
– Spinal Segmental Nerves of S2-S4 Segments
Parasympathetic Output Via the Vagus Nerve or S2-S4
Segmental Nerves
• Preganglionic fibres travel with the branches of
the vagus nerve to reach their targets in the
neck and viscera of the body.
• Or
• Preganglionic fibres from spinal sources (S2-S4)
reach their targets as part of spinal segmental
nerves originating from S2-S4 nerve roots
• They then synapse on postganglionic cells,
which are located in the walls of target organs
• Postganglionic fibres supply glands & smooth
muscle of the following:
– Neck
– Thorax
– Abdomen
– Pelvis
PARASYMPATHETIC OUTFLOW TO
THE HEAD REGION
The Cranial Nerves
• CNI Olfactory
• CNII Optic
• CNIII Oculomotor
• CNIV Trochlear
• CNV Trigeminal
• CNVI Abducent
• CNVII Facial
• CNVIII Vestibulochoclear
• CNIX Glossopharyngeal
• CNX Vagus
• CNXI Accessory
• CNXII Hypoglossal
Cranial Nerves Used in The
Distribution of Autonomic Fibres
• CNIII Oculomotor
• CNVII Facial
• CNIX Glossopharyngeal
• CNX Vagus
PARASYMPATHETIC OUTFLOW
PRE- NERVE ORGAN(S) ACTION
GANGLIONIC HIJACKED BY
NUCLEUS PRE-
GANGLIONICS
EDINGER- III EYE. PUPIL, PUPILLARY
WESTPHAL CILIARY CONSTRICTION
SUPERIOR VII NASAL, SEROUS
SALIVATORY LACRIMAL, SECRETIONS
SUBMANDIB &
SUBLINGUAL GL.
INFERIOR IX PAROTID SEROUS
SALIVATORY SECRETIONS
DORSAL VAGAL X WIDE LARYNGEAL
MOTOR NUCLEUS DISTRIBUTION FUNCTION (i.e.
NECK ONLY) &
Rest of The Body’s
Viscera
ORGANISATION OF SYMPATHETIC
OUTFLOW
X-Section of
Thoracic cord
Dorsal
horn
Lateral
horn
Ventral
horn
General Layout of Sympathetic
Pre-ganglionic Neurones
• All SNS outflow from CNS to peripheral targets
is entirely spinal
• Originates from 14/15 spinal Neural levels
• T1-L2/3
– yet innervates almost all organs of the body
– achieves this end by widely distributing post
ganglionic neurones
• As a general simplification, axons of all pre-
ganglionic neurones either
– terminate immediately in the paravertebral sympathetic
chain of ganglia (also known as the sympathetic trunk)
– or pass through it
SYMPATHETIC PRE-GANGLIONICS
3 POSSIBLE MODES OF TERMINATION OF SYMPATHETIC PRE-
GANGLIONICS
AS THEY DO SO, THEY GIVE RISE TO THE FOLLOWING ANATOMICAL
ENTITIES
WHITE RAMI COMMUNICANTES (OR COMMUNICANS)
GREY RAMI COMMUNICANTES (OR COMMUNICANS)
SPLANCHNIC NERVES
End Lecture Here
