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The Nervous System I: The Autonomic Nervous System (ANS) Anatomy & Physiology Chapter 16 Autonomic Nervous System (ANS) The ANS consists of motor neurons that: ◦ Regulate the action of smooth and cardiac muscle and glands ◦ Make adjustments to ensure optimal support for body activities ◦ Operate via subconscious control Motor Divisions: Somatic vs. Visceral (ANS) Central nervous system (CNS) Peripheral nervous system (PNS) Sensory (afferent) division Motor (efferent) division Somatic nervous system Autonomic nervous system (ANS) Sympathetic division Parasympathetic division Somatic and Autonomic Nervous Systems The two systems differ in ◦ Effectors ◦ Efferent pathways (and their neurotransmitters) ◦ Target organ responses to neurotransmitters Effectors Somatic nervous system ◦ Skeletal muscles ANS ◦ Cardiac muscle ◦ Smooth muscle ◦ Glands Efferent Pathways Somatic nervous system ◦ A, thick, heavily myelinated somatic motor fiber makes up each pathway from the CNS to the muscle ANS pathway is a two-neuron chain 1. Preganglionic neuron (in CNS) has a thin, lightly myelinated preganglionic axon 2. Ganglionic neuron in autonomic ganglion has an unmyelinated postganglionic axon that extends to the effector organ Neurotransmitter Effects Somatic nervous system ◦ All somatic motor neurons release acetylcholine (ACh) ◦ Effects are always stimulatory ANS ◦ Preganglionic fibers release ACh ◦ Postganglionic fibers release norepinephrine or ACh at effectors ◦ Effect is either stimulatory or inhibitory, depending on type of receptors SOMATIC NERVOUS SYSTEM Cell bodies in central nervous system Peripheral nervous system Neurotransmitter at effector Effector organs Single neuron from CNS to effector organs Effect + ACh Stimulatory Heavily myelinated axon Skeletal muscle NE SYMPATHETIC ACh Unmyelinated postganglionic axon Lightly myelinated Ganglion Epinephrine and preganglionic axons norepinephrine ACh Adrenal medulla PARASYMPATHETIC AUTONOMIC NERVOUS SYSTEM Two-neuron chain from CNS to effector organs Acetylcholine (ACh) Blood vessel ACh ACh Lightly myelinated preganglionic axon Norepinephrine (NE) Ganglion + Unmyelinated postganglionic axon Smooth muscle (e.g., in gut), glands, cardiac muscle Stimulatory or inhibitory, depending on neurotransmitter and receptors on effector organs Divisions of the ANS Sympathetic division 2. Parasympathetic division Dual innervation 1. ◦ Almost all visceral organs are served by both divisions, but they cause opposite effects CN III Ciliary ganglion CN VII CN IX CN X Pterygopalatine ganglion Submandibular ganglion Otic ganglion Eye Lacrimal gland Nasal mucosa Submandibular and sublingual glands Parotid gland Heart Cardiac and pulmonary plexuses Celiac plexus Lung Liver and gallbladder Stomach Pancreas S2 S4 Pelvic splanchnic nerves Inferior hypogastric plexus Genitalia (penis, clitoris, and vagina) Large intestine Small intestine Rectum Urinary bladder and ureters Preganglionic Postganglionic Cranial nerve Eye Lacrimal gland Nasal mucosa Pons Sympathetic trunk (chain) ganglia Blood vessels; skin (arrector pili muscles and sweat glands) Superior cervical ganglion T1 Middle cervical ganglion Inferior cervical ganglion Salivary glands Heart Cardiac and pulmonary plexuses Lung Greater splanchnic nerve Lesser splanchnic nerve Celiac ganglion L2 Liver and gallbladder Stomach White rami communicantes Superior mesenteric ganglion Spleen Adrenal medulla Kidney Sacral splanchnic nerves Lumbar splanchnic nerves Inferior mesenteric ganglion Small intestine Large intestine Rectum Preganglionic Postganglionic Genitalia (uterus, vagina, and penis) and urinary bladder Sympathetic nervous system Thoracolumbar area Adrenergic system Activated in the four E’s: excitement, emergency, embarassment, exercise Role of the Sympathetic Division Mobilizes the body during activity; is the “fight-or-flight” system Promotes adjustments during exercise, or when threatened ◦ Blood flow is shunted to skeletal muscles and heart ◦ Bronchioles dilate ◦ Liver releases glucose Parasympathetic nervous system Arise in craniosacral areas Cholinergic system Role of the Parasympathetic Division Promotes maintenance activities and conserves body energy Its activity is illustrated in a person who relaxes, reading, after a meal ◦ Blood pressure, heart rate, and respiratory rates are low ◦ Gastrointestinal tract activity is high ◦ Pupils are constricted and lenses are accommodated for close vision Sympathetic Effects… On the iris - Pupillary dilation On the sweat glands – secretion On piloerector muscles – hair erection (goose bumps) On the heart – increased heart rate and force On blood vessels of skeletal muscle – vasodilation On blood vessels of skin – vasoconstriction On the bronchi and bronchioles – bronchodilation On the kidneys – reduced urine output On the GI Tract – decreased motility and secretion On the Liver – glycogen breakdown On the pancreas – decreased insulin secretion; decreased digestive enzyme secretion On the reproductive system – stimulation of orgasm and relaxation of the uterus Parasympathetic Effects... On the iris - Pupillary constriction On the heart – decreased heart rate and force On blood vessels of skin – vasodilation On the bronchi and bronchioles – bronchoconstriction On the bladder wall – contraction On the GI Tract – increased motility and secretion On the Liver – glycogen synthesis On the pancreas – increased digestive enzyme secretion On the reproductive system – stimulation of penile and clitoral erection Autonomic Nervous System The diagram shows only one side of the body for each division. ZOOMING IN • Which division of the autonomic nervous system has ganglia closer to the effector organ? Cellular Receptors “Docking sites” on postsynaptic cell membranes Two types: Cholinergic receptors ◦ Nicotinic (bind nicotine) on skeletal muscle cells ◦ Muscarinic (bind muscarine, a poison) on effector cells of PNS Adrenergic receptors ◦ Found on receptor cells of sympathetic nervous system ◦ Bind norepinephrine, epinephrine Drugs and the Nervous System sympathomimetics enhance sympathetic activity ◦ stimulate receptors or increase norepinephrine release cold medicines that dilate the bronchioles or constrict nasal blood vessels sympatholytics suppress sympathetic activity ◦ block receptors or inhibit norepinephrine release beta blockers reduce high BP interfering with effects of epinephrine/norepinephrine on heart and blood vessels parasympathomimetics enhance activity while parasympatholytics suppress activity End of Presentation