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 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 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 viscera of thoracic and abdominal cavities some structures of the body wall cutaneous blood vessels sweat glands piloerector muscles carries out actions involuntarily

Visceral Reflexes visceral reflexes - unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors visceral reflex arc receptors – nerve endings that detect stretch, tissue damage, blood chemicals, body temperature, and other internal stimuli afferent neurons – leading to the CNS interneurons – in the CNS efferent neurons – carry motor signals away from the CNS effectors – that make adjustments 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 homeostatic negative feedback loop Glossopharyngeal nerve transmits signals to medulla oblongata 2 Baroreceptors sense increased blood pressure 1 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 heart rate, BP, airflow, blood glucose levels, etc. reduces blood flow to the skin and digestive tract 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 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 heart but inhibits digestive and urinary function, while parasympathetic has the opposite effect

Neural Pathways ANS components are in both the central and peripheral nervous systems control nucleus in hypothalamus and other brainstem areas motor neurons in the spinal cord and peripheral ganglia nerve fibers that travel through the cranial and spinal nerves 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 presynaptic neuron – first neuron (soma in the brainstem or spinal cord) postganglionic neuron – second neuron (axon extends the rest of the way to the target cell)

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 Division: Efferent Pathways Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Eye Pons Salivary glands Preganglionic neurons Postganglionic neurons Regions of spinal cord Cardiac and pulmonary plexuses Heart Cervical Thoracic Lumbar Sacral Celiac ganglion Lung Liver and gallbladder Superior mesenteric ganglion 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

Adrenal Glands paired adrenal glands on superior poles of the kidneys each is two organs with different functions adrenal cortex (outer layer) secretes steroid hormones adrenal medulla (inner core) essentially a sympathetic ganglion 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: Efferent Pathways Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parasympathetic Division: 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 Glossopharyngeal n. (CN IX) Parotid salivary gland Vagus n. (CN X) Cardiac plexus Heart Pulmonary plexus Regions of spinal cord Esophageal plexus Cervical Lung Thoracic Lumbar Celiac ganglion Stomach Sacral Liver and gallbladder Abdominal aortic plexus Spleen Pelvic splanchnic nerves Pancreas Kidney and ureter Inferior hypogastric plexus Descending colon Small intestine Rectum Figure 15.7 Pelvic nerves Ovary Penis Bladder Uterus Scrotum

Enteric Nervous System enteric nervous system – the nervous system of the digestive tract does not arise from the brainstem or spinal cord innervates smooth muscle and glands 100 million neurons found in 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 maybe colonic gangrene, perforation of bowel, and peritonitis usually evident in newborns who fail to have their first bowel movement

Neurotransmitters and Receptors how can different autonomic neurons have different effects? constricting some vessels but dilating others 2 fundamental reasons: sympathetic and parasympathetic fibers secrete different neurotransmitters target cells respond to the same neurotransmitter differently depending upon the type of receptor they have 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 any receptor that binds it is called cholinergic receptor 2 types of cholinergic receptors muscarinic receptors Found in all cardiac muscle, smooth muscle, and gland cells excitatory or inhibitory due to subclasses of muscarinic receptors nicotinic 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 receptors for it called adrenergic receptors alpha-adrenergic receptors usually excitatory 2 subclasses (α1 & α2) beta-adrenergic receptors usually inhibitory 2 subclasses with different effects (β1 & β2)

Neurotransmitters and Receptors (b) Sympathetic adrenergic fiber (c) Sympathetic cholinergic fiber (a) Parasympathetic fiber NE ACh Adrenergic receptor Muscarinic receptor Nicotinic receptor Preganglionic neuron Postganglionic Target cell Muscarinic Neurotransmitters and Receptors Figure 15.8

Overview 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 various hormones, neurotransmitters, and the gas, nitric oxide

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 both divisions do not normally innervate an organ equally

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

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

Dual Innervation cooperative effects - when two divisions act on different effectors to produce a unified effect parasympathetics increase salivary serous cell secretion sympathetics increase salivary mucous cell secretion

Without Dual Innervation some effectors receive only sympathetic fibers adrenal medulla, piloerector muscles, sweat glands and many blood vessels sympathetic vasomotor tone - baseline firing frequency keeps vessels in state of partial constriction increase in firing frequency - vasoconstriction decrease in firing frequency - vasodilation shifts 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 Smooth muscle contraction 2 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 Smooth muscle relaxation 2 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 hypothalamus - major visceral motor control center nuclei for primitive functions – hunger, thirst, sex

Control of Autonomic Function ANS regulated by several levels of CNS midbrain, pons, and medulla oblongata contain: nuclei for cardiac and vasomotor control, salivation, swallowing, sweating, bladder control, and pupillary changes spinal cord reflexes defecation and urination reflexes are integrated in spinal cord we control these functions because of our control over skeletal muscle sphincters…but if the spinal cord is damaged, the reflexes will remain

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 by interfering with effects of epinephrine/norepinephrine on heart and blood vessels

Drugs and the Nervous System parasympathomimetics enhance activity while parasympatholytics suppress activity many drugs also act on neurotransmitters in CNS Prozac blocks reuptake of serotonin to prolong its mood-elevating effect (SSRI: selective serotonin reuptake inhibitor) MAOI’s (monoamine oxidase inhibitors) prevent MAO from breaking down neurotransmitters like NE caffeine competes with adenosine (the presence of which causes sleepiness) by binding to its receptors

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