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

Central nervous system (CNS)Peripheral nervous system (PNS) Motor (efferent) division Sensory (afferent) division Somatic nervous system Autonomic nervous system (ANS) Sympathetic division Parasympathetic division Motor Divisions: Somatic vs. Visceral (ANS)

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

Skeletal muscle Cell bodies in central nervous system Peripheral nervous systemEffect + + Effector organs ACh Smooth muscle (e.g., in gut), glands, cardiac muscle Ganglion Adrenal medullaBlood vessel ACh NE Epinephrine and norepinephrine Acetylcholine (ACh)Norepinephrine (NE) Ganglion Heavily myelinated axon Lightly myelinated preganglionic axon Lightly myelinated preganglionic axons Neuro- transmitter at effector Unmyelinated postganglionic axon Unmyelinated postganglionic axon Stimulatory or inhibitory, depending on neuro- transmitter and receptors on effector organs Single neuron from CNS to effector organs Two-neuron chain from CNS to effector organs SOMATIC NERVOUS SYSTEM AUTONOMIC NERVOUS SYSTEM PARASYMPATHETIC SYMPATHETIC

Divisions of the ANS 1. Sympathetic division 2. Parasympathetic division Dual innervation ◦ Almost all visceral organs are served by both divisions, but they cause opposite effects

Pterygopalatine ganglion Eye Lacrimal gland Nasal mucosa Ciliary ganglion Pterygopalatine ganglion Submandibular ganglion Submandibular and sublingual glands CN III CN VII CN IX CN X Otic ganglion Parotid gland Heart Lung Liver and gallbladder Stomach Pancreas Urinary bladder and ureters Small intestine Large intestine S2S2 Pelvic splanchnic nerves Genitalia (penis, clitoris, and vagina) Rectum Celiac plexus Inferior hypogastric plexus Cardiac and pulmonary plexuses S4S4 Preganglionic Postganglionic Cranial nerve

Superior cervical ganglion Middle cervical ganglion Inferior cervical ganglion Sympathetic trunk (chain) ganglia Pons L2L2 T1T1 White rami communicantes Liver and gallbladder Stomach Spleen Kidney Adrenal medulla Small intestine Large intestine Genitalia (uterus, vagina, and penis) and urinary bladder Celiac ganglion Inferior mesenteric ganglion Lesser splanchnic nerve Greater splanchnic nerve Superior mesenteric ganglion Lumbar splanchnic nerves Eye Lacrimal gland Nasal mucosa Blood vessels; skin (arrector pili muscles and sweat glands) Salivary glands Heart Lung Rectum Cardiac and pulmonary plexuses Preganglionic Postganglionic Sacral splanchnic nerves

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

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? Autonomic Nervous System

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