Autonomic Nervous SystemAutonomic Nervous System

ANHB 2217 – 2006

Avinash Bharadwaj

What Is It Really…?What Is It Really…?

Beyond volitional control – so are reflexes and many other Beyond volitional control – so are reflexes and many other aspects of NS function.aspects of NS function.

Control of involuntary structures – sensory-motor integration?Control of involuntary structures – sensory-motor integration? Is it only the efferent component?Is it only the efferent component? Visceral innervationVisceral innervation Enteric nervous system…Enteric nervous system…

Anatomically NOT a distinct entityAnatomically NOT a distinct entity

Viscera…Viscera…

Viscus = “internal organ”. Smooth/cardiac muscle, Viscus = “internal organ”. Smooth/cardiac muscle, glandsglands

Also include :Also include :Blood vessels, glands in the skinBlood vessels, glands in the skin

Parts of digestive/respiratory systems in the head and Parts of digestive/respiratory systems in the head and the neckthe neck

Efferent And Afferent ComponentsEfferent And Afferent Components

Efferent – to muscle (smooth, cardiac, some Efferent – to muscle (smooth, cardiac, some skeletal) and glands.skeletal) and glands.

Afferent – “visceral” sensationsAfferent – “visceral” sensations Unlike “somatic” sensationsUnlike “somatic” sensations Pressure, stretch and ischaemiaPressure, stretch and ischaemia Sensations ‘used’ for reflex activitySensations ‘used’ for reflex activity Sensations that reach conscious perceptionSensations that reach conscious perception

Efferent Visceral InnervationEfferent Visceral Innervation

““Motor” – may be excitatory or inhibitoryMotor” – may be excitatory or inhibitory Sympathetic and parasympathetic divisions Sympathetic and parasympathetic divisions

Complementary effectsComplementary effects E.g. : Action on the heartE.g. : Action on the heart Different on different target organs : e.g. Different on different target organs : e.g.

sympathetic accelerates the heart but relaxes sympathetic accelerates the heart but relaxes bronchial smooth musclebronchial smooth muscle

Some Common FeaturesSome Common Features

Two neurones between CNS and target (effector) Two neurones between CNS and target (effector) organorgan

Autonomic gangliaAutonomic ganglia Degree of myelination of nerve fibresDegree of myelination of nerve fibres

Two NeuronsTwo NeuronsSomatic

Autonomic

GanglionGanglion Preganglionic fibre (X)Preganglionic fibre (X)

Finely myelinatedFinely myelinated Postganglionic fibre (Y)Postganglionic fibre (Y)

Non-myelinatedNon-myelinated

Sympathetic DivisionSympathetic Division

Preganglionic fibres : axons of neurones in Preganglionic fibres : axons of neurones in thoracic and upper lumbar spinal segmentsthoracic and upper lumbar spinal segments

““Thoracolumbar outflow”Thoracolumbar outflow” Ganglia close to the vertebral columnGanglia close to the vertebral column Postganglionic fibres – through spinal nerves or Postganglionic fibres – through spinal nerves or

splanchnic nerves splanchnic nerves (some preganglionic fibres in splanchnic (some preganglionic fibres in splanchnic nerves)nerves)

Areas beyond the outflow…?Areas beyond the outflow…?

Sympathetic ChainSympathetic Chain

Sympathetic system in red!Sympathetic system in red! Sympathetic chainSympathetic chain Cervical and caudal (lower lumbar Cervical and caudal (lower lumbar

and sacral) gangliaand sacral) ganglia Visceral (splanchnic) distributionVisceral (splanchnic) distribution Glands in the skin, Blood vessels : Glands in the skin, Blood vessels :

along spinal / cranial nervesalong spinal / cranial nerves Spinal nerves : white and grey rami Spinal nerves : white and grey rami

communicantescommunicantes

C

T

L

S

ParasympatheticParasympathetic Craniosacral outflowCraniosacral outflow Ganglia closer to effector organsGanglia closer to effector organs Cranial : Cranial : III, VII, IX, X : III, VII, IX, X :

Ganglia in the head and neckGanglia in the head and neck III – constrictor pupllae, ciliarisIII – constrictor pupllae, ciliaris VII : Lacrimal gland, submandibular VII : Lacrimal gland, submandibular

and sublingual salivary glands, smaller and sublingual salivary glands, smaller glands in the mouth and noseglands in the mouth and nose

IX : Parotid salivary gland, smaller IX : Parotid salivary gland, smaller glands in the pharynx etc.glands in the pharynx etc.

X : Glands in pharynx, trachea, X : Glands in pharynx, trachea, bronchi. Heart, lungs, abdominal bronchi. Heart, lungs, abdominal organsorgans

Sacral : Pelvic organsSacral : Pelvic organs

Higher ControlHigher Control

Hypothalamus and still higher…Hypothalamus and still higher… PathwaysPathways Hypothalamic connectionsHypothalamic connections

Sympathetic effectsSympathetic effects Greater divergence : pre- Greater divergence : pre- postganglionic postganglionic Neurotransmitter re-uptakeNeurotransmitter re-uptake Wisdespread and sustained effectsWisdespread and sustained effects

Parasympathetic effectsParasympathetic effects Less divergenceLess divergence Enzymatic postsynaptic degradationEnzymatic postsynaptic degradation Localised and short-lived effectsLocalised and short-lived effects

Comparisons…Comparisons…

Visceral AfferentsVisceral Afferents

Reflex activity – GI tract, respiratory and othersReflex activity – GI tract, respiratory and others Visceral pain – pathways…?Visceral pain – pathways…? Referred painReferred pain ““Normal sensations” – parasympathetic pathwaysNormal sensations” – parasympathetic pathways ““Warning sensations” – sympathetic pathwaysWarning sensations” – sympathetic pathways

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