Chapter 15 Lecture Outline 15-1 Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 1

Autonomic Nervous System and Visceral Reflexes Autonomic Nervous System (ANS) general properties anatomy Autonomic Effects on Target Organs Central Control of Autonomic Function

Autonomic Nervous System portion of the nervous system that operates in comparative secrecy it manages a multitude of unconscious processes responsible for the body’s homeostasis Walter Cannon coined the expressions as homeostasis and fight or flight dedicated his career to studying the ANS homeostasis cannot be maintained without the ANS

General Properties of ANS autonomic nervous system (ANS) – a motor nervous system that controls glands, cardiac muscle, and smooth muscle also called visceral motor system primary organs of the ANS carries out actions involuntarily – without our conscious intent or awareness

Visceral Reflexes visceral reflexes - unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors and somewhat slower responses visceral reflex arc receptors – nerve endings that detect stretch, tissue damage, blood chemicals, body temperature, and other internal stimuli ANS modifies effector activity

Visceral Reflex to High BP Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. high blood pressure detected by arterial stretch receptors (1), afferent neuron (2) carries signal to CNS, efferent (3) signals travel to the heart (4), heart slows reducing blood pressure 2 Glossopharyngeal nerve transmits signals to medulla oblongata 1 Baroreceptors sense increased blood pressure 3 Vagus nerve transmits inhibitory signals to cardiac pacemaker Common carotid artery Terminal ganglion 4 Heart rate decreases Figure 15.1

Divisions of ANS two divisions innervate same target organs may have cooperative or contrasting effects sympathetic division prepares body for physical activity – exercise, trauma, arousal, competition, anger, or fear parasympathetic division calms many body functions reducing energy expenditure and assists in bodily maintenance digestion and waste elimination “resting and digesting” state

Divisions of ANS autonomic tone - normal background rate of activity that represents the balance of the two systems according to the body’s changing needs parasympathetic tone maintains smooth muscle tone in intestines holds resting heart rate down to about 70 – 80 beats per minute sympathetic tone keeps most blood vessels partially constricted and maintains blood pressure sympathetic division excites the hearts but inhibits digestive and urinary function, while parasympathetic has the opposite effect

Neural Pathways ANS has components in both the central and peripheral nervous systems control nucleus in the hypothalamus and other brainstem regions motor neurons in the spinal cord and peripheral ganglia somatic motor pathway a motor neuron from the brainstem or spinal cord issues a myelinated axon that reaches all the way to the skeletal muscle autonomic pathway signal must travel across two neurons to get to the target organ must cross a synapse where these two neurons meet in an autonomic ganglion

Somatic versus Autonomic Pathways Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Somatic efferent innervation ACh Myelinated fiber Somatic effectors (skeletal muscles) Autonomic efferent innervation ACh ACh or NE Myelinated preganglionic fiber Unmyelinated postganglionic fiber Visceral effectors (cardiac muscle, smooth muscle, glands) Figure 15.2 Autonomic ganglion ANS – two neurons from CNS to effectors presynaptic neuron whose cell body is in CNS postsynaptic neuron cell body in peripheral ganglion

Sympathetic Nervous System also called the thoracolumbar division because it arises from the thoracic and lumbar regions of the spinal cord relatively short preganglionic and long postganglionic fibers lead to nearby sympathetic chain of ganglia (paravertebral ganglia) series of longitudinal ganglia adjacent to both sides of the vertebral column from cervical to coccygeal levels usually 3 cervical, 11 thoracic, 4 lumbar, 4 sacral, and 1 coccygeal ganglion sympathetic nerve fibers are distributed to every level of the body

Sympathetic Nervous System each paravertebral ganglion is connected to a spinal nerve by two branches – communicating rami preganglionic fibers are small myelinated fibers that travel form spinal nerve to the ganglion by way of the white communicating ramus (myelinated) postganglionic fibers leave the ganglion by way of the gray communicating ramus (unmyelinated) forms a bridge back to the spinal nerve postganglionic fibers

Sympathetic Chain Ganglia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cardiac n. Thoracic ganglion Communicating ramus Bronchi Superior vena cava Sympathetic chain Rib Splanchnic n. Phrenic n. Heart Vagus n. Diaphragm © From A Stereoscopic Atlas of Anatomy by David L. Basett. Courtesy of Dr. Robert A. Chase, MD Figure 15.3

Sympathetic Nervous System after entering the sympathetic chain, the postganglionic fibers may follow any of three courses some end in ganglia which they enter and synapse immediately with a postganglionic neuron some travel up or down the chain and synapse in ganglia at other levels some pass through the chain without synapsing and continue as splanchnic nerves

Sympathetic Nervous System nerve fibers leave the sympathetic chain by spinal, sympathetic, and splanchnic nerves spinal nerve route some postganglionic fibers exit a ganglion by way of the gray ramus returns to the spinal nerve and travels the rest of the way to the target organ sympathetic nerve route other nerves leave by way of sympathetic nerves that extend to the heart, lungs, esophagus and thoracic blood vessels these nerves form carotid plexus around each carotid artery of the neck issue fibers from there to the effectors in the head sweat, salivary, nasal glands, piloerector muscles, blood vessels, dilators of iris some fibers of superior and middle cervical ganglia form cardiac nerves to the heart splanchnic nerve route some fibers that arise from spinal nerves T5 to T12 pass through the sympathetic ganglia without synapsing continue on as the splanchnic nerves lead to second set of ganglia – collateral (prevertebral) ganglia and synapse there

Sympathetic Nervous System collateral ganglia contribute to a network called the abdominal aortic plexus wraps around abdominal aorta three major collateral ganglia in this plexus celiac, superior mesenteric, and inferior mesenteric postganglionic fibers accompany these arteries and their branches to their target organs solar plexus – collective name for the celiac and superior mesenteric ganglia nerves radiate from ganglia like rays of the sun neuronal divergence predominates each preganglionic cell branches and synapses on 10 to 20 postganglionic cells one preganglionic neuron can excite multiple postganglionic fibers leading to different target organs have relatively widespread effects

Efferent Pathways Figure 15.4 Eye Pons Salivary glands Heart Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Efferent Pathways Eye Pons Salivary glands Preganglionic neurons Postganglionic neurons Regions of spinal cord Cardiac and pulmonary plexuses Heart Cervical Thoracic Lumbar Sacral Celiac ganglion Lung Superior mesenteric ganglion Liver and gallbladder Stomach Spleen Pancreas Postganglionic fibers to skin, blood vessels, adipose tissue Inferior mesenteric ganglion Small intestine Large intestine Sympathetic chain ganglia Rectum Adrenal medulla Kidney Figure 15.4 Ovary Penis Scrotum Uterus Bladder

Preganglionic Pathways Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Soma of preganglionic neuron To iris, salivary glands, lungs, heart, thoracic blood vessels, esophagus Sympathetic nerve 2 Spinal nerve Somatic motor fiber Preganglionic sympathetic fiber Postganglionic sympathetic fiber To sweat glands, piloerector muscles, and blood vessels of skin and skeletal muscles To somatic effector (skeletal muscle) 1 Soma of somatic motor neuron 3 White ramus Communicating rami Splanchnic nerve Gray ramus Preganglionic neuron Soma of postganglionic neuron Postganglionic neuron Collateral ganglion Somatic neuron Postganglionic sympathetic fibers Sympathetic trunk To liver, spleen, adrenal glands, stomach, intestines, kidneys, urinary bladder, reproductive organs Sympathetic ganglion Figure 15.5 2

Ganglia and Abdominal Aortic Plexus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diaphragm Esophagus Adrenal medulla Adrenal cortex Celiac ganglia (b) Adrenal gland Celiac trunk Superior mesenteric ganglion Renal plexus First lumbar sympathetic ganglion Superior mesenteric artery Kidney Aortic plexus Inferior mesenteric artery Inferior mesenteric ganglion Aorta Figure 15.6 Pelvic sympathetic chain (a)

Summary of Sympathetic Innervation effectors in body wall are innervated by sympathetic fibers in spinal nerves effectors in head and thoracic cavity are innervated by fibers in sympathetic nerves effectors in abdominal cavity are innervated by

Adrenal Glands paired adrenal (suprarenal) glands on superior poles of the kidneys each is two glands with different functions adrenal cortex (outer layer) secretes steroid hormones adrenal medulla (inner core) essentially a sympathetic ganglion consists of modified postganglionic neurons without dendrites or axons stimulated by preganglionic sympathetic neurons that terminate on these cells secretes a mixture of hormones into bloodstream catecholamines - 85% epinephrine (adrenaline) and 15% norepinephrine (noradrenaline) also function as neurotransmitters sympathoadrenal system is the closely related functioning adrenal medulla and sympathetic nervous system

Parasympathetic Division parasympathetic division is also called the craniosacral division arises from the brain and sacral regions of the spinal cord fibers travel in certain cranial and sacral nerves origin of long preganglionic neurons pathways of long preganglionic fibers terminal ganglia in or near target organs long preganglionic, short postganglionic fibers neuronal divergence less than sympathetic division one preganglionic fiber reaches the target organ and then stimulates fewer than 5 postganglionic cells

Parasympathetic Cranial Nerves Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pterygopalatine ganglion Preganglionic neurons Postganglionic neurons Oculomotor nerve (III) narrows pupil and focuses lens Facial nerve (VII) tear, nasal and salivary glands Glossopharyngeal nerve (IX) parotid salivary gland Vagus nerve (X) Oculomotor n. (CN III) Ciliary ganglion Lacrimal gland Eye Facial n. (CN VII) Submandibular ganglion Submandibular salivary gland Otic ganglion Glossopharyngeal n. (CN IX) Parotid salivary gland Vagus n. (CN X) Cardiac plexus Heart Pulmonary plexus Regions of spinal cord Cervical Esophageal plexus Lung Thoracic Lumbar Celiac ganglion Sacral Stomach Abdominal aortic plexus Liver and gallbladder Spleen Pelvic splanchnic nerves Pancreas Kidney and ureter Transverse colon Inferior hypogastric plexus Descending colon Small intestine Rectum Pelvic nerves Ovary Penis Bladder Figure 15.7 Uterus Scrotum

Efferent Pathways Figure 15.7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Efferent Pathways Pterygopalatine ganglion Preganglionic neurons Postganglionic neurons Oculomotor n. (CN III) Ciliary ganglion Lacrimal gland Eye Facial n. (CN VII) Submandibular ganglion Submandibular salivary gland Otic ganglion remaining parasympathetic fibers arise from levels S2 to S4 of the spinal cord form pelvic splanchnic nerves that lead to the inferior hypogastric plexus Glossopharyngeal n. (CN IX) Parotid salivary gland Vagus n. (CN X) Cardiac plexus Heart Pulmonary plexus Regions of spinal cord Cervical Esophageal plexus Lung Thoracic Lumbar Celiac ganglion Sacral Stomach Abdominal aortic plexus Liver and gallbladder Spleen Pelvic splanchnic nerves Pancreas Kidney and ureter Transverse colon Inferior hypogastric plexus Descending colon Small intestine Rectum Figure 15.7 Pelvic nerves Ovary Penis Bladder Uterus Scrotum

Enteric Nervous System composed of 100 million neurons found in the walls of the digestive tract no components in CNS has its own reflex arcs regulates motility of esophagus, stomach, and intestines and secretion of digestive enzymes and acid normal digestive function also requires regulation by sympathetic and parasympathetic systems

Megacolon Hirschsprung disease – hereditary defect causing absence of enteric nervous system no innervation in sigmoid colon and rectum constricts permanently and will not allow passage of feces feces becomes impacted above constriction megacolon – massive dilation of bowel accompanied by abdominal distension and chronic constipation

Neurotransmitters and Receptors how can different autonomic neurons have different effects? constricting some vessels but dilating others effects determined by types of neurotransmitters released and types of receptors found on target cells 2 fundamental reasons: target cells respond to the same neurotransmitter differently depending upon the type of receptor they have for it all autonomic fibers secrete either acetylcholine or norepinephrine there are 2 classes of receptors for each of these neurotransmitters

Acetylcholine (ACh) ACh is secreted by all preganglionic neurons in both divisions and the postganglionic parasympathetic neurons called cholinergic fibers any receptor that binds it is called cholinergic receptor 2 types of cholinergic receptors all cardiac muscle, smooth muscle, and gland cells have muscarinic receptors excitatory or inhibitory due to subclasses of muscarinic receptors on all ANS postganglionic neurons, in the adrenal medulla, and at neuromuscular junctions of skeletal muscle excitatory when ACh binding occurs

Norepinephrine (NE) NE is secreted by nearly all sympathetic postganglionic neurons called adrenergic fibers receptors for it called adrenergic receptors

Overview autonomic effects on glandular secretion are often an indirect result of their effect on blood vessels vasodilation – increased blood flow – increased secretion vasoconstriction – decreased blood flow – decreased secretion sympathetic effects tend to last longer than parasympathetic effects ACh released by parasympathetics is broken down quickly at synapse NE by sympathetics is reabsorbed by nerve, diffuses to adjacent tissues, and much passes into bloodstream many substances released as neurotransmitters that modulate ACh and NE function sympathetic fibers also secrete enkephalin, substance P, neuropeptide Y, somatostatin, neurotensin, or gonadotropin-releasing hormone parasympathetic fibers stimulate endothelial cells to release the gas, nitric oxide – causes vasodilation by inhibiting smooth muscle tone function is crucial to penile erection - means of action of Viagra

Neurotransmitters and Receptors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Parasympathetic fiber Nicotinic receptor ACh Target cell ACh Preganglionic neuron Postganglionic neuron Muscarinic receptor (b) Sympathetic adrenergic fiber Nicotinic receptor ACh Target cell Preganglionic neuron NE Postganglionic neuron Adrenergic receptor (c) Sympathetic cholinergic fiber Nicotinic receptor ACh Target cell Figure 15.8 Preganglionic neuron ACh Postganglionic neuron Muscarinic receptor

Dual Innervation dual innervation - most viscera receive nerve fibers from both parasympathetic and sympathetic divisions antagonistic effect – oppose each other cooperative effects – two divisions act on different effectors to produce a unified overall effect

Dual Innervation antagonistic effects - oppose each other exerted through dual innervation of same effector cells exerted because each division innervates different cells pupillary dilator muscle (sympathetic) dilates pupil constrictor pupillae (parasympathetic) constricts pupil

Dual Innervation cooperative effects - when two divisions act on different effectors to produce a unified effect

Dual Innervation of the Iris Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brain Parasympathetic fibers of oculomotor nerve (III) Sympathetic fibers Superior cervical ganglion Ciliary ganglion Spinal cord Cholinergic stimulation of pupillary constrictor Iris Adrenergic stimulation of pupillary dilator Pupil Sympathetic (adrenergic) effect Parasympathetic (cholinergic) effect Figure 15.9 Pupil dilated Pupil constricted

Without Dual Innervation some effectors receive only sympathetic fibers adrenal medulla, arrector pili muscles, sweat glands and many blood vessels control of blood pressure and routes of blood flow keeps vessels in state of partial constriction increase in firing frequency - vasoconstriction decrease in firing frequency - vasodilation can shift blood flow from one organ to another as needed sympathetic division acting alone can exert opposite effects on the target organ through control of blood vessels during stress blood vessels to muscles and heart dilate blood vessels to skin constrict

Sympathetic and Vasomotor Tone Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Artery sympathetic division prioritizes blood vessels to skeletal muscles and heart in times of emergency 1 Sympathetic nerve fiber 1 Strong sympathetic tone 2 2 Smooth muscle contraction 3 Vasomotor tone 3 Vasoconstriction (a) Vasoconstriction blood vessels to skin vasoconstrict to minimize bleeding if injury occurs during stress or exercise 1 1 Weaker sympathetic tone 2 2 Smooth muscle relaxation 3 3 Vasodilation (b) Vasodilation Figure 15.10

Control of Autonomic Function ANS regulated by several levels of CNS cerebral cortex has an influence – anger, fear, anxiety powerful emotions influence the ANS because of the connections between our limbic system and the hypothalamus spinal cord reflexes defecation and micturition reflexes are integrated in spinal cord we control these functions because of our control over skeletal muscle sphincters…if the spinal cord is damaged, the smooth muscle of bowel and bladder is controlled by autonomic reflexes built into the spinal cord

Drugs and the Nervous System neuropharmacology – study of effects of drugs on 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

Adenosine and Caffeine Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. NH2 N N O CH3 H3C N N N N OH O O N N CH3 OH OH Figure 15.11 Adenosine Caffeine