Autonomic Nervous System ANHB 2217 – 2006 Avinash Bharadwaj

What Is It Really…? Beyond volitional control – so are reflexes and many other aspects of NS function. Beyond volitional control – so are reflexes and many other 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 innervation Visceral innervation Enteric nervous system… Enteric nervous system… Anatomically NOT a distinct entity

Viscera… Viscus = “internal organ”. Smooth/cardiac muscle, glands Also include : Blood vessels, glands in the skin Parts of digestive/respiratory systems in the head and the neck

Efferent And Afferent Components Efferent – to muscle (smooth, cardiac, some skeletal) and glands. Efferent – to muscle (smooth, cardiac, some skeletal) and glands. Afferent – “visceral” sensations Afferent – “visceral” sensations Unlike “somatic” sensations Unlike “somatic” sensations Pressure, stretch and ischaemia Pressure, stretch and ischaemia Sensations ‘used’ for reflex activity Sensations ‘used’ for reflex activity Sensations that reach conscious perception Sensations that reach conscious perception

Efferent Visceral Innervation “Motor” – may be excitatory or inhibitory “Motor” – may be excitatory or inhibitory Sympathetic and parasympathetic divisions Sympathetic and parasympathetic divisions Complementary effects Complementary effects E.g. : Action on the heart E.g. : Action on the heart Different on different target organs : e.g. sympathetic accelerates the heart but relaxes bronchial smooth muscle Different on different target organs : e.g. sympathetic accelerates the heart but relaxes bronchial smooth muscle

Some Common Features Two neurones between CNS and target (effector) organ Two neurones between CNS and target (effector) organ Autonomic ganglia Autonomic ganglia Degree of myelination of nerve fibres Degree of myelination of nerve fibres

Two Neurons Somatic Autonomic Ganglion Ganglion Preganglionic fibre (X) Preganglionic fibre (X) Finely myelinated Finely myelinated Postganglionic fibre (Y) Postganglionic fibre (Y) Non-myelinated Non-myelinated

Sympathetic Division Preganglionic fibres : axons of neurones in thoracic and upper lumbar spinal segments Preganglionic fibres : axons of neurones in thoracic and upper lumbar spinal segments “Thoracolumbar outflow” “Thoracolumbar outflow” Ganglia close to the vertebral column Ganglia close to the vertebral column Postganglionic fibres – through spinal nerves or splanchnic nerves (some preganglionic fibres in splanchnic nerves) Postganglionic fibres – through spinal nerves or splanchnic nerves (some preganglionic fibres in splanchnic nerves) Areas beyond the outflow…? Areas beyond the outflow…?

Sympathetic Chain Sympathetic system in red! Sympathetic system in red! Sympathetic chain Sympathetic chain Cervical and caudal (lower lumbar and sacral) ganglia Cervical and caudal (lower lumbar and sacral) ganglia Visceral (splanchnic) distribution Visceral (splanchnic) distribution Glands in the skin, Blood vessels : along spinal / cranial nerves Glands in the skin, Blood vessels : along spinal / cranial nerves Spinal nerves : white and grey rami communicantes Spinal nerves : white and grey rami communicantes C T L S

Parasympathetic Craniosacral outflow Craniosacral outflow Ganglia closer to effector organs Ganglia closer to effector organs Cranial : III, VII, IX, X : Ganglia in the head and neck Cranial : III, VII, IX, X : Ganglia in the head and neck III – constrictor pupllae, ciliaris III – constrictor pupllae, ciliaris VII : Lacrimal gland, submandibular and sublingual salivary glands, smaller glands in the mouth and nose VII : Lacrimal gland, submandibular and sublingual salivary glands, smaller glands in the mouth and nose IX : Parotid salivary gland, smaller glands in the pharynx etc. IX : Parotid salivary gland, smaller glands in the pharynx etc. X : Glands in pharynx, trachea, bronchi. Heart, lungs, abdominal organs X : Glands in pharynx, trachea, bronchi. Heart, lungs, abdominal organs Sacral : Pelvic organs Sacral : Pelvic organs

Higher Control Hypothalamus and still higher… Hypothalamus and still higher… Pathways Pathways Hypothalamic connections Hypothalamic connections

Sympathetic effects Sympathetic effects Greater divergence : pre-  postganglionic Greater divergence : pre-  postganglionic Neurotransmitter re-uptake Neurotransmitter re-uptake Wisdespread and sustained effects Wisdespread and sustained effects Parasympathetic effects Parasympathetic effects Less divergence Less divergence Enzymatic postsynaptic degradation Enzymatic postsynaptic degradation Localised and short-lived effects Localised and short-lived effects Comparisons…

Visceral Afferents Reflex activity – GI tract, respiratory and others Reflex activity – GI tract, respiratory and others Visceral pain – pathways…? Visceral pain – pathways…? Referred pain Referred pain “Normal sensations” – parasympathetic pathways “Normal sensations” – parasympathetic pathways “Warning sensations” – sympathetic pathways “Warning sensations” – sympathetic pathways Last Slide