Autonomic Nervous System ANHB 2217 2006 Avinash Bharadwaj

Autonomic Nervous System ANHB 2217 – 2006 Avinash Bharadwaj

What Is It Really…? Anatomically NOT a distinct entity n n n Beyond volitional control – so are reflexes and many other aspects of NS function. Control of involuntary structures – sensory-motor integration? Is it only the efferent component? Visceral innervation Enteric nervous system…

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

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

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

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

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

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

Parasympathetic n n n Craniosacral outflow Ganglia closer to effector organs Cranial : III, VII, IX, X : Ganglia in the head and neck n n n III – constrictor pupllae, ciliaris 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. X : Glands in pharynx, trachea, bronchi. Heart, lungs, abdominal organs Sacral : Pelvic organs

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

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

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