The Nervous System I: The Autonomic Nervous System (ANS)

1. The Nervous System I:The Autonomic Nervous System (ANS) Anatomy & Physiology Chapter 16

2. 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

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

4. Somatic and Autonomic Nervous Systems • The two systems differ in • Effectors • Efferent pathways (and their neurotransmitters) • Target organ responses to neurotransmitters

5. Effectors • Somatic nervous system • Skeletal muscles • ANS • Cardiac muscle • Smooth muscle • Glands

6. 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 • Preganglionic neuron (in CNS) has a thin, lightly myelinated preganglionic axon • Ganglionic neuron in autonomic ganglion has an unmyelinated postganglionic axon that extends to the effector organ

7. 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

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

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

10. Eye Ciliary ganglion CN III Lacrimal gland CN VII Pterygopalatine ganglion Pterygopalatine ganglion Nasal mucosa CN IX CN X Submandibular ganglion Submandibular and sublingual glands Otic ganglion Parotid gland Heart Cardiac and pulmonary plexuses Lung Liver and gallbladder Celiac plexus Stomach Pancreas S2 Large intestine S4 Pelvic splanchnic nerves Small intestine Rectum Inferior hypogastric plexus Urinary bladder and ureters Preganglionic Genitalia (penis, clitoris, and vagina) Postganglionic Cranial nerve

11. Eye Lacrimal gland Nasal mucosa Pons Sympathetic trunk (chain) ganglia Blood vessels; skin (arrector pili muscles and sweat glands) Superior cervical ganglion Salivary glands Middle cervical ganglion Heart Inferior cervical ganglion Cardiac and pulmonary plexuses Lung T1 Greater splanchnic nerve Lesser splanchnic nerve Liver and gallbladder Celiac ganglion L2 Stomach Superior mesenteric ganglion White rami communicantes Spleen Adrenal medulla Kidney Sacral splanchnic nerves Lumbar splanchnic nerves Small intestine Inferior mesenteric ganglion Large intestine Rectum Preganglionic Postganglionic Genitalia (uterus, vagina, and penis) and urinary bladder

12. Sympathetic nervous system • Thoracolumbar area • Adrenergic system • Activated in the four E’s: excitement, emergency, embarassment, exercise

13. 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

14. Parasympathetic nervous system • Arise in craniosacral areas • Cholinergic system

15. 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

16. 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

17. 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

18. 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?

19. 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

20. 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

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