The Autonomic Nervous System and Visceral Sensory Neurons

Home , Autonomic ganglion, Esophageal plexus, Pulmonary plexus, Ramus communicans

PowerPoint® Lecture Slides The ANS and Visceral Sensory Neurons prepared by Leslie Hendon • The ANS—a system of motor neurons University of Alabama, Birmingham • Innervates • Smooth muscle • Cardiac muscle C H A P T E R 15 • Glands • Regulates visceral functions such as… Part 1 • Heart rate The Autonomic • Blood pressure • Digestion Nervous System • Urination and Visceral • The ANS is the General visceral motor division of Sensory Neurons the PNS

The Autonomic Nervous System Comparison of Autonomic and Somatic and Visceral Sensory Neurons Motor Systems • Somatic motor system • One motor neuron extends from the CNS to skeletal muscle • Axons are well myelinated, conduct impulses rapidly • Autonomic nervous system • Chain of two motor neurons • Preganglionic neuron • Ganglionic neuron • Conduction is slower than somatic nervous system due to • Thinly myelinated or unmyelinated axons • Motor neuron synapses in a ganglion

Figure 15.2 Comparing Somatic Motor and Autonomic Innervation Autonomic and Somatic Motor Systems

Cell bodies in central Neurotransmitter Effector nervous system Peripheral nervous system at effector organs Effect Single neuron from CNS to effector organs ACh

SYSTEM SYSTEM Stimulatory SOMATIC SOMATIC NERVOUS NERVOUS Heavily myelinated axon Skeletal muscle Two-neuron chain from CNS to effector organs

ACh NE

Unmyelinated postganglionic axon Lightly myelinated Ganglion preganglionic axons Epinephrine and ACh norepinephrine SYMPATHETIC SYMPATHETIC Stimulatory or inhibitory, depending Adrenal medulla Blood vessel on neurotransmitter and receptors on effector ACh ACh Smooth muscle organs AUTONOMIC NERVOUS SYSTEM SYSTEM NERVOUS AUTONOMIC (e.g., in gut), glands, Lightly myelinated Unmyelinated cardiac muscle preganglionic axon Ganglion postganglionic axon PARASYMPATHETIC PARASYMPATHETIC

1 Divisions of the Autonomic Nervous System Divisions of the Autonomic Nervous System

• Sympathetic and parasympathetic • Sympathetic—“fight, flight, or fright” divisions • Activated during EXTREME situations • Chains of two motor neurons • Exercise • Innervate mostly the same structures • Excitement • Cause opposite effects (usually) • Emergencies • Sympathetic division mobilizes the body during extreme situations • Parasympathetic division controls routine maintenance functions

Divisions of the Autonomic Nervous System Divisions of the Autonomic Nervous System

• Sympathetic responses help us respond to • Parasympathetic division dangerous situations • Active when the body is at rest • Increase heart rate and breathing rate • Concerned with conserving energy • Increases blood and oxygen to skeletal • Directs “housekeeping” activities: “rest & muscles digest” • Dilates pupils and airways • Heart rate and breathing are at low-normal • Motility of the digestive tract and urinary tracts levels are inhibited • Gastrointestinal tract digests food • Pupils are constricted

Anatomical Differences in Sympathetic Anatomical Differences in Sympathetic and Parasympathetic Divisions and Parasympathetic Divisions Parasympathetic Sympathetic

Eye Eye • 1. Issue from Brain stem • 2. Length of postganglionic fibers Salivary Skin* different regions of glands Cranial • Sympathetic—long postganglionic fibers Salivary Sympathetic glands the CNS ganglia Heart Cervical • Parasympathetic—short postganglionic • Sympathetic—also Lungs Lungs fibers T called the 1 Heart

thoracolumbar Stomach • 3. Branching of axons Thoracic division Stomach Pancreas • Sympathetic axons—highly branched Liver • Parasympathetic— Pancreas and gall- • Influences many organs L1 bladder

also called the Liver and Adrenal gall- Lumbar gland • Parasympathetic axons—few branches craniosacral division bladder

Bladder • Localized effect Bladder Genitals Genitals Sacral

2 Anatomical Differences in Sympathetic Parasympathetic and Sympathetic Divisions and Parasympathetic Divisions • 4. Neurotransmitter released by postganglionic axons • Sympathetic • Most release norepinephrine (adrenergic) • Parasympathetic • Release acetylcholine (cholinergic)

A. The Parasympathetic Division The Parasympathetic Division

CN III Ciliary Eye ganglion Lacrimal gland CN VII Pterygopalatine CN IX Nasal ganglion mucosa CN X Submandibular ganglion • Cranial outflow Submandibular and sublingual glands Otic ganglion • Comes from the brain Parotid gland

Heart Cardiac and Innervates organs of the head, neck, thorax, pulmonary • plexuses and abdomen Lung

Liver and Sacral outflow gallbladder • Celiac plexus • Innervation supplies remaining abdominal Stomach Pancreas

and pelvic organs S 2 Large S intestine 4

Pelvic Small splanchnic intestine nerves Inferior Rectum hypogastric plexus

Urinary bladder and ureters Genitalia (penis, clitoris, and vagina) Preganglionic Postganglionic CN Cranial nerve Copyright © 2011 Pearson Education, Inc. Copyright © 2011 Pearson Education, Inc. Figure 15.4

Cranial Outflow (Parasympathetic) Outflow via the Oculomotor Nerve (III)

• Preganglionic fibers travel in 4 C.N.s: • Parasympathetic fibers innervate smooth • Oculomotor nerve (III) muscles in the eye • Facial nerve (VII) • Cause pupil constriction • Glossopharyngeal nerve (IX) • Preganglionic cell bodies • Vagus nerve (X) • Located in the oculomotor nucleus in the midbrain • Cell bodies of C.N.s located in cranial nerve nuclei in the • Ganglionic cell bodies brain stem • Lie in the ciliary ganglion

3 Outflow via the Facial Nerve (VII) Outflow via the Glossopharyngeal Nerve (IX)

• Parasympathetic fibers stimulate secretion • Parasympathetic fibers of glands in the head • Stimulate secretion of glands in the head • Lacrimal nucleus • Lacrimal nucleus—located in the pons • Located in the pons • Synapse in the pterygopalatine ganglion • Synapse in the pterygopalatine ganglion • Superior salivatory nucleus—located in the • Superior salivatory nucleus pons • Located in the pons • Synapse in the submandibular ganglion • Synapse in the submandibular ganglion

Outflow via the Vagus Nerve (X) Path of the Vagus Nerve

• Fibers innervate visceral organs of the thorax and most of the abdomen • Sends branches through • Stimulates: • Autonomic nerve plexuses • Digestion, reduction in heart rate, and reduction in blood pressure • Cardiac plexus • Pulmonary plexus • Preganglionic cell bodies • Esophageal plexus • Located in dorsal motor nucleus in the medulla • Celiac plexus • Postganglionic neurons • Superior mesenteric plexus • Confined within the walls of organs being innervated • Cell bodies form intramural ganglia

Autonomic nerves, plexuses and ganglia Sacral Outflow Superior cervical Left vagus nerve ganglion Cardiac branches • Emerges from S2–S4

Middle cervical Trachea of the vagus • Innervates organs of the pelvis and lower abdomen ganglion Thoracic spinal Stellate ganglion nerves (ventral rami) Cardiac plexus Sympathetic cardiac nerves Pulmonary plexus • Preganglionic cell bodies Aorta on the bronchus Aortic arch Vagus nerve • Located in visceral motor region of spinal gray Sympathetic Esophageal plexus trunk ganglia Diaphragm matter Stomach with Esophagus vagus nerve • Axons run in ventral roots to ventral rami Thoracic Celiac ganglion splanchnic and plexus • Form pelvic splanchnic nerves nerves Superior mesenteric ganglion and plexus • Run through the inferior hypogastric plexus Adrenal Aortic plexus (suprarenal) Inferior mesenteric gland ganglion and plexus Kidney Superior hypogastric Lumbar plexus and sacral Inferior hypogastric splanchnic (pelvic) plexus nerves Pelvic sympathetic trunk

4 B. The Sympathetic Division Sympathetic Trunk Ganglia

• Basic organization • Located on both sides of the vertebral

• Issues from T1–L2 column • Preganglionic cell bodies form the lateral • Linked by short nerves into sympathetic gray horn trunks • Supplies visceral organs and structures of • Sympathetic trunk ganglia are also called superficial body regions • ‘Chain’ ganglia • Contains more ganglia than the • ‘Paravertebral’ ganglia parasympathetic division

Sympathetic Trunk Ganglia Sympathetic Trunk Ganglia Spinal cord Dorsal root Lateral horn Dorsal root (visceral Ventral root Dorsal root ganglion motor zone) Rib Dorsal ramus of spinal nerve Ventral ramus of • Joined to ventral rami by white and gray Sympathetic spinal nerve trunk ganglion Gray ramus communicans Ventral root Sympathetic rami communicantes White ramus Sympathetic trunk communicans Ventral ramus trunk ganglion of spinal nerve Sympathetic trunk Skin (arrector 1 Synapse at the same level • Fusion of ganglia  fewer ganglia than spinal Gray ramus pili muscles communicans and sweat White ramus glands) To effector nerves communicans Thoracic splanchnic nerves Blood vessels • Fusion of ganglia most apparent in the (a) Location of the sympathetic trunk cervical region

Splanchnic nerve • Superior, middle, and inferior cervical ganglia Collateral ganglion (such as the celiac)

Skin (arrector pili muscles Target organ and sweat in abdomen glands) To effector (e.g., intestine)

2 Synapse at a higher or lower level 3 Synapse in a distant collateral Blood vessels ganglion anterior to the vertebral column (b) Three pathways of sympathetic innervation

Collateral Ganglia… Sympathetic Pathways

• Differ from sympathetic trunk ganglia in three • Preganglionic neurons in the thoracolumbar ways spinal cord send motor axons through: • Unpaired, not segmentally arranged • Adjacent ventral root into • Occur only in abdomen and pelvis • Spinal nerve, then the • Lie anterior to the vertebral column • White ramus communicans • Main ganglia • And to the associated sympathetic • Celiac, superior mesenteric, inferior trunk ganglion mesenteric, and inferior hypogastric ganglia

5 Sympathetic Pathways Sympathetic Pathways

Dorsal root Lateral horn (visceral Dorsal root ganglion motor zone) • Preganglionic axons follow one of three Dorsal ramus of spinal nerve Ventral ramus of pathways spinal nerve Gray ramus communicans Ventral root White ramus Sympathetic communicans 1. Synapes with a postganglionic neuron at the trunk ganglion Sympathetic trunk Skin (arrector 1 same level and exit on a spinal nerve at that pili muscles Synapse at the same level and sweat level glands) To effector

2. Axon ascends or descends in the Blood vessels sympathetic trunk to synapse in another ganglion

Splanchnic nerve 3. Axon passes through the sympathetic trunk Collateral ganglion and exits on a splanchnic nerve (such as the celiac) Skin (arrector pili muscles Target organ and sweat in abdomen glands) To effector (e.g., intestine)

2 Synapse at a higher or lower level 3 Synapse in a distant collateral Blood vessels ganglion anterior to the vertebral column (b) Three pathways of sympathetic innervation

Sympathetic Pathways to the Body Periphery: Pathways to the Body Periphery

• Innervate • Preganglionic fibers enter the sympathetic • Sweat glands trunk ganglia and synapse there • Arrector pili muscles • Some preganglionic fibers travel superiorly • Peripheral blood vessels or inferiorly on the sympathetic trunk • Postganglionic axons travel in gray rami communicantes

Pathways to the Body Periphery Sympathetic Pathways to the Head

• Gray and white rami communicantes • Preganglionic fibers originate in spinal cord

• Gray rami—contain only postganglionic fibers at T1–T4 traveling to peripheral structures • Fibers ascend in the sympathetic trunk • Fibers are unmyelinated • Synapse in superior cervical ganglion • White rami—contain preganglionic fibers traveling to sympathetic trunk ganglia • Fibers are myelinated

6 Sympathetic Pathways to the Head Sympathetic Pathways to Thoracic Organs

• Postganglionic fibers associate with large • Preganglionic fibers originate at spinal levels

arteries T1–T6 • Carried by these structures to • Some fibers synapse in nearest sympathetic • Glands trunk ganglion • Smooth muscle • Postganglionic fibers run directly to the • Vessels throughout the head organ supplied

Sympathetic Pathways to Thoracic Organs Sympathetic Pathways to Thoracic Organs Eye Lacrimal gland Pons Nasal mucosa Sympathetic trunk (chain) ganglia Blood vessels; skin (arrector pili • Sympathetic fibers to heart have a less Superior muscles and cervical sweat glands) ganglion Middle Salivary glands direct route cervical ganglion Heart Inferior cervical Cardiac and ganglion Lung • Functions T pulmonary 1 plexuses Greater splanchnic nerve • Increase heart rate Lesser splanchnic nerve Liver and gallbladder • Dilate bronchioles Celiac ganglion L 2 Stomach Dilate blood vessels to the heart wall White rami Superior • Spleen communicantes mesenteric ganglion Adrenal medulla • Inhibit muscles and glands in the esophagus Sacral Kidney splanchnic nerves Lumbar and digestive system Small splanchnic Inferior intestine nerves mesenteric ganglion Large intestine Rectum Preganglionic Postganglionic

Sympathetic Pathways to Abdominal Organs Sympathetic Pathways to the Pelvic Organs

• Preganglionic fibers originate in the spinal cord from T10–L2 • Preganglionic fibers originate in spinal cord • Fibers descend in the sympathetic trunk to lumbar and sacral ganglia (T5–L2) • Some postganglionic fibers run in lumbar and sacral • Pass through adjacent sympathetic trunk splanchnic nerves to plexuses ganglia • Inferior mesenteric plexus, aortic plexus, or hypogastric plexus • Then travel in thoracic splanchnic nerves • Other preganglionic fibers pass directly to autonomic plexuses and • Synapse in prevertebral ganglia on the synapse in collateral ganglia abdominal aorta • Inferior mesenteric ganglia or inferior hypogastric ganglia • Postganglionic fibers go from these plexuses to the • Celiac and superior mesenteric ganglia • Bladder, reproductive organs, and distal large intestine • Inhibit activity of muscles and glands in visceral organs

7 The Role of the Adrenal Medulla in the The Adrenal Medulla

Sympathetic Division Sympathetic trunk

Major organ of the sympathetic nervous • Spinal cord: T –L Ventral system 8 1 root Thoracic • Constitutes largest sympathetic ganglia splanchnic nerves • Secretes great quantities of norepinephrine and adrenaline Kidney • Stimulated to secrete by preganglionic Adrenal gland sympathetic fibers Adrenal medulla Epinephrine and norepinephrine

Visceral Sensory Neurons

• General visceral sensory neurons monitor • Stretch, temperature, chemical changes, and irritation • Cell bodies are located in the dorsal root ganglion • Visceral pain • No pain results when visceral organs are cut • Visceral pain results from chemical irritation or inflammation • Visceral pain often perceived to be of somatic origin • Phenomenon of referred pain

8 A Map of Referred Pain Visceral Reflexes

Heart • Visceral sensory and autonomic neurons Lungs and diaphragm • Participate in visceral reflex arcs Liver • Defecation reflex Heart Gallbladder Liver • Micturition reflex Appendix Stomach Pancreas • Some are simple spinal reflexes Small intestine Ovaries • Others do not involve the CNS Colon Kidneys • Strictly peripheral reflexes Urinary bladder Ureters

Visceral Reflex Arc Visceral Reflex Arc Stimulus Increased blood pressure

Dorsal root ganglion 1 Sensory receptor in viscera 1 Baroreceptors in carotid sinus are 3 Spinal cord stimulated. 2 Visceral sensory 2 neuron 2 Sensory impulses are carried on visceral 4 3 Integration center sensory fibers in the •May be preganglionic glossopharyngeal 1 neuron (as shown) nerves (CN IX). •May be a dorsal horn interneuron 3 Integration occurs in •May be within walls cardiac center of of gastrointestinal medulla oblongata. tract Autonomic ganglion 4 Efferent pathway via 4 Efferent pathway the vagus nerves (CN X) (two-neuron chain) •Preganglionic neuron 5 Parasympathetic •Postganglionic stimulation of heart neuron decreases heart rate. 5

5 Visceral effector Blood pressure decreases

Figure 15.13 Levels of ANS control. Communication at Central Control of the ANS subconscious level

• ANS is not under direct voluntary control Cerebral cortex (frontal lobe) • Activities regulated by CNS

• Brain stem Limbic system (emotional input) • Spinal cord Hypothalamus The “boss”: Overall • Hypothalamus integration of ANS • Amygdaloid body Brain stem (reticular formation, etc.) • Cerebral cortex Regulates pupil size, heart, blood pressure, airflow, salivation, etc.

Spinal cord Reflexes for urination, defecation, erection, and ejaculation

9 Control by the Brain Stem and Spinal Cord Control by the Hypothalamus and Amygdala

• Control by the brain stem and spinal cord • Hypothalamus—the main integration center • Reticular formation exerts most direct of the ANS influence • Medial and anterior parts • Medulla oblongata • Direct parasympathetic functions • Periaqueductal gray matter • Lateral and posterior parts • Direct sympathetic functions • Amygdaloid body • Main limbic region for emotions

Control by the Cerebral Cortex Disorders of the Autonomic Nervous System

• People can exert some control over • Raynaud’s disease—characterized by autonomic functions constriction of blood vessels • Feelings of calm during meditation • Provoked by exposure to cold or by emotional • Influence of cerebral cortex on stress parasympathetic centers in hypothalamus • Voluntary sympathetic response • Recalling scary event

Disorders of the Autonomic Nervous System The ANS Throughout Life

• Achalasia of the cardia • Preganglionic neurons of the ANS develop • Defect in the autonomic innervation of the from the neural tube esophagus • Postganglionic neurons develop from the • Congenital megacolon (Hirschsprung’s neural crest disease) • Development of the sympathetic division • Birth defect • Some cells migrate ventrally • Parasympathetic innervation of distal large • Form the sympathetic trunk ganglia intestine fails to develop correctly • Other cells migrate • Feces and gas accumulate proximal to • Form the prevertebral ganglia defect

10 Figure 15.15 Embryonic development of some sympathetic structures, including the adrenal medulla. Dorsal The ANS Throughout Life Neural crest Neural tube (future dorsal root ganglion) • Efficiency of the ANS declines with Sympathetic Aorta advancing age trunk ganglion • Constipation due to reduced mobility of Collateral ganglion cells gastrointestinal (GI) tract Adrenal medulla • Dry eyes due to reduced tear formation cells Cortex of adrenal (suprarenal) Urogenital gland ridge (kidney) Coelom Organ plexus

Digestive tube