chapter 18 *lecture outline copyright © the mcgraw-hill companies, inc. permission required for...

Chapter 18

*Lecture Outline

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Chapter 18 Outline• Comparison of the Somatic and Autonomic

Nervous Systems• Overview of the Autonomic Nervous System• Parasympathetic Division• Sympathetic Division• Other Features of the Autonomic Nervous

System• CNS Control of Autonomic Function• Development of the Autonomic Nervous System

Autonomic Nervous System

• The autonomic nervous system (ANS) is a complex system of nerves that govern involuntary actions.

• The ANS works constantly with the somatic nervous system (SNS) to regulate body organs and maintain normal internal functions.

Autonomic Nervous System

• The ANS and SNS are part of both the central nervous system and the peripheral nervous system.

• The SNS operates under our conscious control. The ANS functions are involuntary and we are usually unaware of them.

Comparison of Somatic and Autonomic Nervous Systems

Figure 18.1


• Both the SNS and the ANS use sensory and motor neurons.

• In the SNS, somatic motor neurons innervate skeletal muscle fibers, causing conscious voluntary movement.

• ANS motor neurons innervate smooth muscle fibers, cardiac muscle fibers, or glands.

• ANS motor neurons can either excite or inhibit cells in the viscera.


• SNS—single lower motor neuron axon extends uninterrupted from the spinal cord to one or more muscle fibers

• ANS—two-neuron chain innervates muscles and glands

Components of the Autonomic Nervous System

Figure 18.2

Comparison of Somatic and Autonomic Motor Nervous Systems

Two-Neuron Chain in ANS• The first neuron in the ANS pathway is the

preganglionic neuron. Its cell body is in the brain or spinal cord.

• A preganglionic axon extends to the second cell body housed within an autonomic ganglion in the peripheral nervous system.

• The second neuron in the pathway is called a ganglionic neuron.

• A postganglionic axon extends from its cell body to effector (target) cells.

Two-Neuron Chain in ANS

• Neuronal convergence—axons from numerous preganglionic cells synapse on a single ganglionic cell

• Neuronal divergence—axons from one preganglionic cell synapse on numerous ganglionic cells

Divisions of AutonomicNervous System

• Parasympathetic division—conservation of energy and replenishment of nutrient stores (“rest-and-digest”)

• Sympathetic division—preparation of body for emergencies (“fight-or-flight”); increased activity of this division results in increased alertness and metabolic activity

Comparison of Parasympathetic and Sympathetic Divisions

Figure 18.3

Anatomic Differences Between Parasympathetic and Sympathetic Neurons

Figure 18.4

Comparison of Sympathetic and Parasympathetic Divisions

Parasympathetic Division

• Termed craniosacral division because preganglionic neurons are housed within nuclei in the brainstem and within lateral gray regions of the S2–S4 spinal cord segments

• Ganglionic neurons are found in either terminal ganglia close to the target organ, or intramural ganglia in the wall of the target organ

Overview of Parasympathetic Pathways

Figure 18.5

Four Cranial Nerves of Parasympathetic Division

1. Oculomotor (CN III)

2. Facial (CN VII)

3. Glossopharyngeal (CN IX)

4. Vagus (CN X)

Oculomotor Nerve (CN III)

• Preganglionic cell bodies housed in nuclei in mesencephalon

• Postganglionic cell bodies located in ciliary ganglion within the orbit

• Postganglionic axons project to the ciliary muscle and to the pupillary constrictor muscle of iris

Facial Nerve (VII)

Two branches of preganglionic axons in the facial nerve (VII) exit the pons:

1. greater petrosal nerve

2. chorda tympani

Facial Nerve (VII)

Greater petrosal nerve:• terminates at the pterygopalatine

ganglion • postganglionic axons project to

lacrimal glands and small glands of nasal cavity, oral cavity, and palate

Facial Nerve (VII)

Chorda tympani:• terminates at the submandibular

ganglion – postganglionic axons project to

submandibular and sublingual salivary glands in the floor of the mouth

Glossopharyngeal Nerve (CN IX)

• Preganglionic axons exit brainstem• Preganglionic axons branch and

synapse on ganglionic neurons in the otic ganglion

• Postganglionic axons cause increase in secretion from parotid salivary glands

Vagus Nerve (CN X)

• Projects inferiorly through neck to supply innervation to thoracic organs and most abdominal organs

• Multiple branches extend to thoracic organs to increase mucous production and decrease diameter of airways, and to decrease heart rate and force of heart contraction

Vagus Nerve (CN X)

• Vagal trunks pass through diaphragm, associate with the abdominal aorta, and project branches to ganglia located adjacent to or within wall of target organs

• Increases smooth muscle motility and secretory activity in digestive tract organs

Spinal Sacral Nerves

• Preganglionic neuron cell bodies are housed within lateral gray regions of S2–S4 spinal cord segments.

• Preganglionic axons branch to form pelvic splanchnic nerves, which contribute to the superior and inferior hypogastric plexus.

• Preganglionic fibers project to ganglionic neurons within terminal or intramural ganglia of large intestine, rectum, reproductive organs, urinary bladder, and distal ureter.

Parasympathetic Division Outflow

Sympathetic Division

• Also termed thoracolumbar division because preganglionic neuron cell bodies are housed in lateral horn between first thoracic (T1) and second lumbar (L2) spinal segments

• Preganglionic axons travel with somatic motor neuron axons to exit the spinal cord and enter the anterior roots and then the T1–L2 spinal nerves

Right and LeftSympathetic Trunks

• Sympathetic trunks are located anterior to spinal nerves and immediately lateral to vertebral column.

• Sympathetic trunk ganglia (paravertebral or chain ganglia) house sympathetic ganglionic neuron cell bodies. One sympathetic ganglion is approximately associated with each spinal nerve.

• Cervical portion of each sympathetic trunk is partitioned into three ganglia: the superior, middle, and inferior ganglia.

Overview of Sympathetic Pathways

Figure 18.6


Superior cervical ganglion

Middle cervical ganglion

Inferior cervical ganglion

T1

T2

T3

T1T1

T2

T3

Eye

Salivary glands

Heart

Blood vessels

LungGreater thoracic splanchnic nerve

Stomach

Spleen

Pancreas

Small intestine

Large intestine

Adrenal medullaKidney

Celiac ganglion

Lesser thoracic splanchnic nerve

Preganglionic

Postganglionic

T4

T5

T6

T7

T8

T9

T10

T11

T12

L1

L2

T4

T5

T6

T7

T8

T9

T10

T11

T12

L1

L2L2

Sympathetic chain ganglia

Spinal cord

L3

L4

L5

S1

S2

Rectum

Ovary Uterus

Prostate

Seminal vesicleVas deferens

BladderHypogastric plexusLumbar splanchnic nerves

Sacral splanchnic nerves

Least thoracic splanchnic nerve

Ureter (proximal)

Ureter (distal)

Testis

Right Left

Blood vessels andsweat glands of head

Cardiac andpulmonaryplexuses

Liver andgallbladder

Superiormesenteric

ganglion

Inferiormesentericganglion

Postganglionic fibersto skin, blood vessels

Sympathetic Trunk

Figure 18.7

Cervical Sympathetic Ganglia

• Postganglionic axons from cell bodies in the superior cervical ganglion distribute to structures in the head and neck. Axons innervate sweat glands, smooth muscle in blood vessels, dilator pupillae muscle of the eye, and the superior tarsal muscle of the eye.

• Middle and inferior cervical ganglia house neuron cell bodies that extend postganglionic axons to the thoracic viscera.

Rami Communicantes

• Connect sympathetic trunk to each spinal nerve

• Preganglionic sympathetic axons of T1–L2 spinal nerves are carried by white rami communicantes (or white rami)

Rami Communicantes

• Postganglionic sympathetic axons are carried from the sympathetic trunk to the spinal nerve by gray rami communicantes (or gray rami). Gray rami connect to all spinal nerves including cervical, sacral, and coccygeal spinal nerves.

• Preganglionic axons of white rami are myelinated and postganglionic axons of gray rami are unmyelinated.

Splanchnic Nerves

• Composed of preganglionic sympathetic axons that did not synapse in a sympathetic trunk ganglion

• Run anteriorly from sympathetic trunk to most of viscera

Splanchnic Nerves

• Larger nerves are preganglionic axons that extend from sympathetic trunk ganglia:– Greater thoracic splanchnic nerves: T5–T9– Lesser thoracic splanchnic nerves: T10–T11– Least thoracic splanchnic nerves: T12– Lumbar splanchnic nerves: L1 and L2– Sacral splanchnic nerves: sacral sympathetic

ganglia

Prevertebral (Collateral) Ganglia

• Splanchnic nerves typically terminate in prevertebral ganglia.

• Ganglia are unpaired and immediately anterior to the vertebral column on the anterolateral surface of the aorta in the abdominopelvic cavity.

Prevertebral (Collateral) Ganglia

• Ganglia typically cluster around the major abdominal arteries and are named for the arteries.

• Sympathetic postganglionic axons extend away from the ganglionic neuron cell bodies in the ganglia and innervate many of the abdominal organs.

Prevertebral Ganglia

Prevertebral ganglia include:• Celiac ganglion• Superior mesenteric ganglion • Inferior mesenteric ganglion

Celiac Ganglion

• Location—adjacent to origin of celiac artery

• Preganglion axons—greater thoracic splanchnic nerves (T5–T9 segment of spinal cord)

• Postganglionic axons—innervate stomach, spleen, liver, gallbladder, proximal duodenum, part of pancreas

Superior Mesenteric Ganglion

• Location—adjacent to origin of superior mesenteric artery

• Preganglionic axons—lesser and least thoracic splanchnic nerves (T10–T12 segment of spinal cord)

• Postganglionic axons—innervate distal duodenum, part of pancreas, remainder of small intestine, proximal large intestine, kidneys, proximal part of ureters

Inferior Mesenteric Ganglion

• Location—adjacent to the origin of the inferior mesenteric artery

• Preganglionic axons—lumbar splanchnic nerves (L1–L2 segment of spinal cord)

• Postganglionic axons—innervate the distal colon, rectum, urinary bladder, distal ureter, and most of reproductive organs

Sympathetic Pathways

• All preganglionic neurons originate in lateral gray horns of T1–L2 regions of the spinal cord.

• Preganglionic axons travel with T1–L2 spinal nerves.

• Preganglionic axons immediately leave spinal nerve and travel through white rami to enter sympathetic trunk.

Sympathetic Pathways• Once inside the sympathetic trunk

preganglionic axons may remain at the level of entry or travel superiorly or inferiorly within the sympathetic trunk.

• Axons exit sympathetic trunk ganglia by:– spinal nerve pathway– postganglionic sympathetic nerve pathway– splanchnic nerve pathway– adrenal medulla pathway

Spinal Nerve Pathway

Figure 18.8

Postganglionic Sympathetic Nerve Pathway

Figure 18.8

Splanchnic Nerve Pathway

Figure 18.8

Adrenal Medulla Pathway

Figure 18.8

Adrenal Medulla Pathway

• Adrenal medulla—the internal region of adrenal gland that releases hormones within the bloodstream to help promote fight-or-flight response– The hormones are epinephrine and, to a

lesser degree, norepinephrine

Sympathetic Outflow

Autonomic Plexuses

• Collections of sympathetic postganglionic axons, parasympathetic preganglionic axons, and visceral sensory axons

• Sympathetic and parasympathetic axons are close to one another

Autonomic Plexuses

• Cardiac plexus

• Pulmonary plexus

• Esophageal plexus

• Abdominal aortic plexus consists of celiac plexus, superior mesenteric plexus, inferior mesenteric plexus,

• Hypogastric plexus

Autonomic Plexuses

Figure 18.9

Cardiac Plexus• In mediastinum of thoracic cavity • Consists of postganglionic sympathetic axons

from thoracic sympathetic trunk ganglia and preganglionic axons of vagus nerve

• Increased sympathetic activity increases heart rate and blood pressure

• Increased parasympathetic activity decreases heart rate

Pulmonary Plexus

• Consists of postganglionic sympathetic axons from thoracic sympathetic trunk ganglia and preganglionic axons from the vagus nerve

• Axons project to bronchi and blood vessels of the lungs

• Parasympathetic stimulation reduces bronchial diameter (bronchoconstriction) and increases mucous gland secretion in bronchial tree

• Sympathetic innervation causes bronchodilation (increase bronchial diameter)

Esophageal Plexus

• Consists of preganglionic axons from the vagus nerve

• Parasympathetic activity coordinates smooth muscle activity during swallowing reflex in inferior wall and cardiac sphincter in inferior esophagus

Abdominal Aortic Plexus

• Consists of celiac plexus, superior mesenteric plexus, and inferior mesenteric plexus

• Composed of postganglionic axons projecting from the prevertebral ganglia and preganglionic axons from the vagus nerve

Hypogastric Plexus

• Complex meshwork of postganglionic sympathetic axons (from the aortic plexus and the lumbar region of the sympathetic trunk) and preganglionic parasympathetic axons from the pelvic splanchnic nerve

• Axons innervate viscera within the pelvic region

Neurotransmitters and Receptors

• All preganglionic axons release acetylcholine (ACh), which has an excitatory effect on the ganglionic cell.

• All postganglionic parasympathetic axons and a few postganglionic sympathetic axons release ACh on the effector.

• Depending on the receptor, ACh from parasympathetic axons may have either an inhibitory or excitatory effect on the effector.

Neurotransmitters and Receptors

• Ach released from sympathetic axons is excitatory only.

• Most postganglionic sympathetic axons release norepinephrine on the effector.

• Depending on the receptor, the effects of norepinephrine has an inhibitory or an excitatory effect.

Comparison of Neurotransmitters in the Autonomic Nervous System

Figure 18.10


Parasympathetic Pathway Sympathetic Pathways

Preganglionic axon releases ACh

ACh ACh

Target cell

ACh

Target cell Target cell

AChACh NE

Ganglionic neuron cell body anddendrites always contain receptorsfor ACh

Postganglionic axon releasesACh or NE

Target cells contain either AChreceptors (bind ACh) or NEreceptors (bind NE)

AChreceptors

AChreceptors

AChreceptors

NEreceptors

AChreceptors

AChreceptors

Dual Innervation

• Many visceral effectors have dual innervation, meaning innervation by postganglionic axons from both ANS divisions.

• The actions of the divisions usually oppose each other (antagonistic effects).

Autonomic Reflexes

Figure 18.11


4

Spinal cord

Interneuron

Urinary bladder

Ureters

Ureter

Detrusor muscle contracts

1

23

5

Pelvic splanchnic nerve

Urinarybladderstretchesas it fillswith urine

Stimulusactivatesreceptor

Nerve impulse travels through sensoryneuron to integration center in the spinal cord Nerve impulse is processed

in the integration center

Motor impulses areconducted throughmotor neurons

Postganglionicaxon

Effector responds toimpulse from motor neuron(smooth muscle contractionoccurs in the bladder walland relaxation in the internalurethral sphincter)

Internal urethral sphincterrelaxes

CNS Control of Autonomic Function

Autonomic function is influenced by the:

• cerebrum

• hypothalamus

• brainstem

• spinal cord

Control of Autonomic Functions by Higher Brain Centers

Figure 18.12


Cerebrum:• ANS activities are affected by conscious

activities in cerebral cortex and subconscious communication between association areas in the cortex with centers of sympathetic and parasympathetic control in the hypothalamus.

• Sensory processing in the thalamus and emotional states controlled in the limbic system directly affect the hypothalamus.


Hypothalamus:• Integration and command center for

autonomic functions• Contains nuclei that control visceral functions

in both divisions of the ANS• Communicates with other CNS regions,

including cerebral cortex, thalamus, brainstem, cerebellum, and spinal cord

• Central brain structure involved in emotions and drives that act through the ANS


Brainstem:• Nuclei in the mesencephalon, pons, medulla

oblongata mediate visceral reflexes.• Reflex centers control accommodation of the

lens, blood pressure changes, blood vessel diameter changes, digestive activities, heart rate changes, and pupil size.

• Centers for cardiac, digestive, and vasomotor functions are housed within the brainstem.


Spinal Cord:• Processes some autonomic responses,

notably the parasympathetic activities associated with defecation and urination, without involvement of the brain

• Higher centers in the brain may consciously inhibit these reflex activities

Neural Crest Cell Derivatives

Figure 18.13

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