Autonomic Nervous System

AUTONOMIC NERVOUS SYSTEM

AUTONOMIC NERVOUS SYSTEM • Introduction • Classification • Organization of Neurons • Sympathetic Nervous System • Parasympathetic Nervous System • Applied aspects

Introduction Hypothalamus -- Head ganglion Prefrontal cortex & Limbic lobe also controls Important for the Vegetative function of the Nervous system

Classification Functional : Sympathetic x Parasympathetic (Enteric nervous system) Anatomical : Thoraco - Lumbar outflow Slide 19 Cranio-sacral outflow Chemical : Adrenergic x Cholinergic

Organisation of Neurons Ach

SNS

nor

Ad

PNS

Ach

Ach

Sympathetic Nervous system Central controlling part – Post Hypothalamus Lateral Horn cells of the spinal cord T1 – L2 Afferent fibres – Pain sensation (Viscera) Efferent fibres – Pre & post ganglionic neurons

Preganglionic neurons: Arise from lateral horn cells ( T1 – L2) -Para vertebral chain of ganglia

Slide 24, Slide 23

-Ascend/descend ; synapse on the same chain Slide 21 -few without synapsing ; synapses at peripheral collateral ganglia eg) superior Slide 27 mesentric ganglia

Postganglionic neuron: -- Peripheral sympathetic ganglions Slide 24 -- Axons – postganglionic nerve fibres -- Iris, lacrimal glands ,salivary glands, Slide 20 -- CVS ,RS, GIT, Kidney, Bladder, Uterus, MRS -- Phaeochromocytes (Adrenal Medulla)

Exception in NT in SNS : sweat glands & blood vessels to skeletal muscle – Cholinergic Mechanism of action: Quick massive action along with adrenal medulla + stress situations + Fight/flight. Receptors: { α & β } α1& α2 Blood vessels – VC Sphincters

-- contraction

Iris

-- contraction

Pilomotor

-- contraction

β1&β2 receptors: Heart rate & FOC Bronchial SM relaxation Ureter, bladder & Intestine- relaxation Drugs that block α-receptors : Phenoxybenzamine Pentolomine β-blockers : Propanolol Butaxamine

Parasympathetic nervous system Control centre – Anterior Hypothalamus Afferent fibres – Volume & pressure changes/viscera Efferent fibres – secretomotor : viscera Cranial division : Slide 23 Preganglionic : Edinger –Westpal Nucleus Sup. Salivary nucleus Inferior salivary nucleus Dorsal vagal nucleus

Ganglion lies near the target organ or within the organ. Cranial outflow is from, Cranial nerves III,VII,IX,X. Supplies -- CVS, RS, GIT up to transverse colon. Sacral division : S2,S3,S4 -- Pelvic nerve Supplies – Descending colon, sigmoid colon, rectum, Urinary bladder, erectile tissue of penis & Uterus. Slide 23

Mechanism of action: Snipping action – as 1:1 ratio of post & preganglionic neurons Ach –NT Muscarinic – eg) Pilocarpine ,( Atropine –blocker) Nicotinic -- NMJ ( Curarine) PSNS – Anabolic system SNS --Catabolic system(Glycogenolysis/lipolysis)

Central control of the ANS Spinal cord Medulla Oblongata Hypothalamus Limbic system Cerebral cortex

Functions of autonomic nervous system 1.Controls the involuntary muscle activities eg) heart ,blood vessels, GIT motility, Visceral & sexual reflexes. 2.Controls secretion from the exocrine & endocrine glands 3.Role in body homeostasis. - Blood volume regulation - ECF volume regulation

-- BP regulation -- Blood –glucose regulation 4, Role in stress ; -- SNS – Glycogenolysis , lipolysis 5, Role in emotions 6, Control of respiration -- bronchial dilatation 7, Regulation of body Temperature, -- Hypothalamus – regulation of body T0 sweat glands

8, Role in metabolism : CHO & lipid catabolism SNS -Blood glucose & FFA levels 9, Controls the sensitivity of sensory receptors -- chemo, baro, muscle spindle -- Olfactory receptors -- taste receptors

Applied aspects: - α, β & ganglionic blockers –Hypertension/PVD - Sympathectomy – (-)vasospasm& blood flow - Hypotension following high spinal anesthesia is due to paralysis of sympathetic flow to splanchnic nerves. - Autonomic insufficiency - postural hypotension - retention of urine - constipation etc

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