Year 1 Block GBMS3 ANS PDF

Basic Medical Sciences Year 1 Block: GBMS3 ANS Dr Mohamed Elkawafi 1  Objectives 1. Outline general organization of nervous system. 2....

Basic Medical Sciences Year 1 Block: GBMS3 ANS Dr Mohamed Elkawafi 1  Objectives 1. Outline general organization of nervous system. 2. Discuss General organization of the autonomic nervous system 3. Receptors on the effector organs 4. Discuss effects of sympathetic and parasympathetic stimulaion on specific organ 5. Describe Function of the adrenal medullae 6. Discuss Selective stimulation of target organs by sympathetic and parasympathetic systems or “mass discharge 7. Compare between somatic and autonomic nervous system. 2 Nervous system organization 3 Somatic VS autonomic nervous system 4  Autonomic nervous system (ANS) ANS is a set of pathways to and from the central nervous system (CNS) that innervates and regulates smooth muscle, cardiac muscle, and glands The ANS help to regulate Autonomic ganglia: synapses located in peripheral structures Arterial blood pressure Preganglionic neurons: neurons that travel from the CNS to the ganglia are GIT motility and secretion Postganglionic neurons: neurons that travel from the ganglia to the effector organs Urinary bladder emptying Body temperature Sweating And many more functions. 5 Parasympathetic nervous system “rest & digest” Also called the craniosacral system because all its preganglionic neurons are in the brain stem or sacral levels of the spinal cord Cranial nerves III, VII, IX and X In lateral horn of gray matter from S2 -S4 6 Sympathetic Nervous System The sympathetic nervous system emerge from the thoracic and lumbar portions of the spinal cord The sympathetic nervous system is some- times called the thoracolumbar division of the autonomic nervous system. The preganglionic neurons originate in a region of gray matter called the lateral horn or the intermediolateral cell column. 7 In general, sympathetic ganglia are located close to the central nervous system, whereas parasympathetic ganglia are located close to the effector tissues. Therefore, sympathetic pathway has short pre-ganglionic fibres and long post-ganglionic fibres, whereas parasympathetic pathway has long pre-ganglionic fibres and short postganglionic fibres. 8  Functions of autonomic nervous system Most of the visceral organs have dual innervation, i.e. are supplied by both sympathetic and parasympathetic divisions of ANS. This is called dual intervention The two divisions produce antagonistic effects on each organ and provide a very fine degree of control over the effector organ. Some of the visceral organs are innervated by one division of ANS only; Ø Uterus, adrenal medulla and most of the arterioles are innervated by sympathetic division only. Ø Glands of stomach and pancreas are innervated by parasympathetic division only. 9 10  Autonomic neurotransmitters and receptors Parasympathetic fibres 1. Pre-ganglionic fibres: acetylcholine 2. Post-ganglionic fibres: acetylcholine Sympathetic fibres 1. Pre-ganglionic fibres: acetylcholine 2. Post-ganglionic fibres: Adrenergic fibres: Norepinephrine (mainly), or epinephrine (All post-ganglionic sympathetic fibres other than cholinergic). Cholinergic fibres: Acetylcholine (the post-ganglionic sympathetic cholinergic nerve fibres supplying sweat glands, blood vessels in heart and skeletal muscles). 11  All pre-ganglionic fibres (sympathetic as well as parasympathetic) release acetylcholine. All post-ganglionic parasympathetic fibres release acetylcholine. Most post-ganglionic sympathetic (adrenergic) fibres release norepinephrine. A few post-ganglionic sympathetic (cholinergic) fibres release acetylcholine 12 13 Nonadrenergic, noncholinergic neurons Nonadrenergic, noncholinergic neurons include some postganglionic parasympathetic neurons of the GIT, which release substance P, vasoactive intestinal peptide (VIP), or nitric oxide (NO). 14  Autonomic receptors Autonomic neurotransmitters (acetylcholine or norepinephrine) produce their effects on the organs by combining with specific protein molecules known as receptors 1. Cholinergic receptors Nicotinic receptors and Muscarinic receptors. 2. Adrenergic receptors Alpha (α) adrenergic receptors (which are of further two types: α1 and α2) and Beta (β) adrenergic receptors (which are of further three types: β1, β2 and β3). 15 Nicotinic receptors Location: These receptors are located in/at: Autonomic ganglia of sympathetic and parasympathetic nervous system, Neuromuscular junction and Adrenal medulla. Effect: These receptors produce excitation. Muscarinic receptors Location: Muscarinic receptors are located in the: Heart, Smooth muscles (except vascular smooth muscle) and Glands. Effects: Inhibitory effect in the heart, e.g. decreased heart rate and decreased conduction velocity in atrioventricular (AV) node. Excitatory effect in smooth muscle and glands (e.g. increased gastrointestinal motility and increased secretion). 16 α1 receptors Location: Vascular smooth muscles of skin and splanchnic regions. Gastrointestinal and bladder sphincters. Radial muscles of the iris. Effect: These receptors produce excitation e.g. contraction or constriction. α2 receptors Location: Pre-synaptic nerve terminals, Platelets, Fat cells Walls of the gastrointestinal tract. Effect: Often produce inhibition (e.g. relaxation or dilatation 17 β1 receptors Location: Sinoatrial (SA) node & Atrioventricular (AV) node Ventricular muscles of the heart Effect: These receptors produce excitation (e.g. increased heart rate, increased conduction velocity and increased contractility).. β2 receptors Location: Vascular smooth muscle of skeletal muscle, β3 receptors Bronchial smooth muscle, Location: Walls of the GIT & Bladder The adipose tissue Effect: These receptors produce relaxation (e.g. dilation of vascular Effect: causes lipolysis. smooth muscle, dilation of bronchioles and relaxation of bladder wall). 18 IP3 = inositol triphosphate 19 20 References 21