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An Overview on the Physiologic Anatomy of the Autonomic Nervous System Rabiu AbduSSALAM Magaji, Ph.D. Bayero University, Kano, Nigeria. IBRO-SfN-NAS Teaching Tools Workshop in Neuroscience, Fayoum Egypt, 2-6th December, 2009 Target Audience 9First Year Medical Students Objectives Students should be able to list: 9The divisions of the ANS 9Structure of the ANS 9Functions of the ANS DIVISIONS OF THE NERVOUS SYSTEM THE AUTONOMIC NERVOUS SYSTEM ¾The autonomic nervous system (ANS) regulates physiologic processes without conscious control. ¾The ANS consists of two sets of nerve bodies: preganglionic and postganglionic fibers. ¾The two major divisions of the ANS are the sympathetic and parasympathetic systems. Anatomy of the Autonomic Nervous System Sympathetic: 9The preganglionic cell bodies of the sympathetic system are located in the intermediolateral horn of the spinal cord between T1 and L2 or L3. 9The sympathetic ganglia are adjacent to the spine and consist of the vertebral (sympathetic chain) and prevertebral ganglia 9Long fibers run from these ganglia to effector organs, including the smooth muscle of blood vessels, viscera, lungs, scalp (piloerector muscles), and pupils; the heart; and glands (sweat, salivary, and digestive). Parasympathetic The preganglionic cell bodies of the parasympathetic system are located in the nuclei of the brain stem and sacral portion of the spinal cord (S2-S4). These preganglionic fibers exit the brain stem with the 3rd, 7th, 9th, and 10th cranial nerves. Parasympathetic ganglia are located in the blood vessels of the head, neck, and thoracoabdominal viscera; lacrimal and salivary glands; smooth muscle of viscera and glands. Postganglionic parasympathetic fibers are relatively short (only about 1 or 2 mm long) thereby producing specific, localized responses in the effector organs. Inputs to the Autonomic Nervous System ¾ The ANS receives input from parts of the CNS that process and integrate stimuli from the body and external environment. ¾ These parts include the hypothalamus, nucleus of the solitary tract, reticular formation, amygdala, hippocampus, and olfactory cortex. Neurotransmitters of the ANS Two most common neurotransmitters released by neurons of the ANS are acetylcholine (cholinergic) and norepinephrine/noradrenaline (adrenergic). Acetylcholine: All preganglionic nerve fibers All postganglionic fibers of the parasympathetic system Sympathetic postganglionic fibers innervating sweat glands Adrenaline: In most sympathetic postganglionic fibers Receptors of the ANS Neurotransmitters Cholinergic receptors: nicotinic or muscarinic. Adrenergic receptors: alpha (α) and beta (β), with α being more abundant. The adrenergic receptors are further divided into (α1, α2, β1 and β2) according to some factors. Functions of the ANS 9 The two divisions of the ANS are dominant under different conditions. 9 The sympathetic system is activated during emergency “fight-or-flight” reactions and during exercise. 9 The parasympathetic system is predominant during quiet conditions (“rest and digest”). As such, the physiological effects caused by each system are quite predictable. 9 In other words, all of the changes in organ and tissue function induced by the sympathetic system work together to support strenuous physical activity and the changes induced by the parasympathetic system are appropriate for when the body is resting. Summary ANS as a division of the NS is concerned with the control of visceral functions. Sympathetic and parasympathetic divisions of the ANS are anatomically and physiologically distinct. Both the two divisions work together to make the ANS functions possible.