14 The Autonomic Nervous System

© 2011 Pearson Education, Inc.

PowerPoint® Lecture Presentations prepared byAlexander G. CheroskeMesa Community College at Red Mountain

14The Autonomic Nervous System


Section 1: ANS Functional Anatomy and Organization

• Learning Outcomes

• 14.1 List the divisions of the ANS and the general functions of each.

• 14.2 Describe the structures and functions of the sympathetic and

parasympathetic divisions of the autonomic nervous system.

• 14.3 Describe the innervation patterns of the sympathetic and parasympathetic

divisions of the autonomic nervous system.




• 14.4 Describe the various types of sympathetic and parasympathetic receptors and

their associated neurotransmitters.

• 14.5 Describe the mechanisms of neurotransmitter release in the ANS,

and explain the effects of neurotransmitters on target organs and tissues.



• Comparisons of somatic nervous system (SNS) and autonomic nervous system (ANS)

• SNS

• Motor neurons exert voluntary control over skeletal muscles

• Lower motor neurons may be controlled by

• Reflexes based in spinal cord

• Upper motor neurons with cell bodies in brain nuclei or at primary motor cortex

Animation: Somatic Autonomic Nervous System

© 2011 Pearson Education, Inc.Figure 14 Section 1 1

A schematic of the somatic nervous system(SNS), which provides conscious and sub-Conscious control over skeletal muscles

BRAIN

Upper motorneurons in

primary motorcortex

Skeletalmuscle

Skeletalmuscle

Lowermotor

neurons

Spinal cord

Somaticmotornuclei ofspinal cord

Somatic motornuclei of brain

stem



• Comparisons of somatic nervous system (SNS) and autonomic nervous system (ANS) (continued)

• ANS

• CNS motor neurons synapse with visceral motor neurons in autonomic ganglia, which control visceral effectors

• Integrative centers located in hypothalamus• Comparable to SNS upper motor neurons

• Two types of visceral motor neurons1. Preganglionic neurons (cell bodies in CNS)

• Activities represent direct reflex responses

§ Ganglionic neurons (cell bodies in autonomic ganglia)

• Innervate effectors like cardiac and smooth muscle

© 2011 Pearson Education, Inc.Figure 14 Section 1 2

Preganglionicneuron

Visceral Effectors

Smoothmuscle

Glands

Cardiacmuscle

Adipocytes

A schematic of the autonomicnervous system (ANS), whichcontrols visceral functions largelyoutside our awareness

Preganglionicneuron

Ganglionicneurons

Autonomicganglia

Autonomicnuclei inspinal cord

Spinalcord

Autonomicnuclei inbrain stem

Visceral motornuclei in

hypothalamus BRAIN


Module 14.1: ANS divisions

• Three ANS divisions

1. Sympathetic (or thoracolumbar) division

• Axons emerge from thoracic and superior lumbar segments of spinal cord

• Innervate ganglia relatively close to spinal cord

• “Kicks in” only during periods of exertion, stress, or emergency

2. Parasympathetic (or craniosacral) division

• Axons emerge from brain stem and sacral spinal segments

• Innervate ganglia very close (or within) target organs

• Most often, effects are opposite to sympathetic

© 2011 Pearson Education, Inc.Figure 14.1 1

Autonomic Nervous System

Sympathetic Division Parasympathetic Division

In the sympathetic division, or thoracolumbar(thor-a-kō-LUM-bar) division, axons emerge from the thoracic and superior lumbar segments of the spinal cord and innervate ganglia relatively close to the spinal cord.

In the parasympathetic division, or cranio-sacral (krā-nē-ō-SĀ-krul) divions, axonsemerge from the brain stem and the sacralsegments of the spinal cord, and they innervateganglia very close to (or within) target organs.

The two main divisionsof the ANS: the sympatheticand parasympatheticdivisions

Cranial nerves(III, VII, IX, andX)

T1T2

T3

T4

T5

T6

T7

T8

T9

T10

T11

T12

L1

L2

S2

S3

S4

Sacral nerves(S2, S3, S4 only)

Lumbar nerves(L1, L2 only)

Thoracicnerves


Module 14.1: ANS divisions

• Three ANS divisions (continued)

3. Enteric nervous system (ENS)

• Extensive network of neurons (~100 million) and nerve networks within walls of digestive tract

• Influenced by sympathetic and parasympathetic divisions

• However, many complex visceral activities are coordinated on a local level (without CNS instructions)

• Will be discussed more in Ch. 21 (Digestive System)


The extensive system of neurons andnerve networks of the enteric nervoussystem (ENS)

Esophagus

Stomach

Large intestine

Small intestine


Representative plexuses, ganglia,and nerves of the sympathetic andparasympathetic divisions

Pelvic symaptheticchain

Hypogastric plexus

Inferior mesentericplexus and ganglion

Superior mesentericganglion

Celiac plexusand ganglion

Esophageal plexus

Thoracic sympatheticchain ganglia

Pulmonary plexus

Cardiac plexus

Autonomic Plexusesand Ganglia

Right vagus nerve

Aortic arch

Trachea

Esophagus

Diaphragm

Superior mesentericartery

Inferior mesentericartery

Thoracic spinalnerves

Left vagus nerve

Splanchnic nerves


Module 14.1 Review

a. Identify the major divisions of the autonomic nervous system.

b. What division of the ANS is responsible for the physiological changes you experience when startled by a loud noise?

c. Compare the anatomy of the sympathetic division with the parasympathetic division.


Module 14.2: Autonomic ganglia

• Autonomic ganglia

• Sympathetic division

• Preganglionic fibers (neurons) are relatively short while postganglionic fibers (neurons) are relatively long

• Accordingly, sympathetic ganglia (where these fibers synapse) are relatively near spinal cord

• Specific ganglia

1. Sympathetic chain (on either side of spinal cord)

• Innervates visceral effectors in thoracic cavity, head, body wall, and limbs



• Sympathetic division (continued)

• Specific ganglia (continued)

2. Collateral ganglia (within abdominopelvic cavity)• Includes celiac, superior, and inferior mesenteric

ganglia

• Innervates visceral effectors in abdominopelvic cavity

3. Adrenal medulla• Center of adrenal gland

• Acts as endocrine gland

• Targets organs and systems throughout body




• Prepares body for heightened levels of somatic activity

• Known as “fight or flight” division

• Typical responses

1. Heightened mental alertness

2. Increased metabolic rate

3. Reduced digestive and urinary functions

4. Activation of energy reserves

5. Increased respiratory rate and dilation of passageways

6. Elevated heart rate and blood pressure

7. Activation of sweat glands


Organization of the sympathetic division of the ANS

PreganglionicNeurons

Lateral grayhorns ofspinalsegmentsT1-L2

Ganglionic Neurons

Each sympathetic chainconsists of a series ofinterconnected ganglialocated on either side of thevertebral column.

The collateral ganglia,located within theabdominopelvic cavity,include the celiac, superiormesenteric, and inferiormesenteric ganglia.

The center of each adrenalgland contains a sympatheticganglion, the adrenalmedulla, that acts as anendocrine organ.

Ganglionic neurons inthe sympathetic chainand collateral gangliaexert their effectsthrough innervationof peripheral targetorgans.

Ganglionic neurons inthe adrenal medullaeaffect target organsthroughout the bodythrough the release ofhormones into thegeneral circulation.

Target Organs

Organs andsystemsthroughout thebody

Visceral effectorsin abdomino-pelvic cavity

Visceral effectorsin thoracic cavity,head, body wall,and limbs

KEY

Preganglionic fibers

Postganglionic fibers

Hormones releasedinto circulation



• Parasympathetic division

• Typical preganglionic fiber synapses on 6–8 ganglionic neurons

• May be situated in:

• Terminal ganglia (near target organ)

• Usually paired

• Ciliary ganglion (intrinsic eye muscles)

• Pterygopalatine and submandibular ganglia (nasal, tear, and salivary glands)

• Otic ganglion (parotid salivary gland)



• Parasympathetic division (continued)

• Typical preganglionic fiber synapses on 6–8 ganglionic neurons (continued)

• May be situated in: (continued)

• Intramural (murus, wall) ganglia (embedded in target organ wall)

• Typically interconnected masses/clusters of cells

• Innervate visceral organs of neck, and of thoracic and abdominopelvic cavities



• Parasympathetic division (continued)

• Concerned with regulation of visceral function and energy conservation

• Known as “rest and digest” system

• Typical responses

1. Decreased metabolic rate

2. Decreased heart rate and blood pressure

3. Increased salivary and digestive gland secretion

4. Increased digestive tract motility and blood flow

5. Stimulation of urination and defecation


Organization of the parasympathetic division of the ANS

KEY

Preganglionic fibers

Postganglionic fibers

PreganglionicNeurons

Ganglionic Neurons Target Organs

In sacral segments of thespinal cord, parasympatheticnuclei lie in the lateral grayhorns of spinal segmentsS2–S4.

The midbrain, pons,and medulla oblongatacontain parasympatheticnuclei associated withcranial nerves III, VII, IX,and X.

Pelvicnerves

III

VII

IX

X

Ciliary ganglion

Pterygopalatine andsubmandibularganglia

Otic ganglion

Intramural ganglia

Intramural ganglia

Visceral organs ininferior portion ofabdominopelviccavity

Visceral organs of neck,thoracic cavity,and most ofabdominal cavity

Parotid salivary gland

Nasal glands, tearglands, and salivaryglands

Intrinsic eye muscles(pupil and lens shape)


Module 14.2 Review

a. List general responses to increased sympathetic activity and to parasympathetic activity.

b. Describe an intramural ganglion.

c. Starting in the spinal cord, trace the path of a nerve impulse through the sympathetic ANS to its target organ in the abdominopelvic cavity.


Module 14.3: Autonomic innervation patterns

• Autonomic innervation patterns


• Every spinal nerve has a gray ramus carrying sympathetic postganglionic fibers

• Preganglionic fibers passing to collateral ganglia form splanchnic nerves

• Postganglionic fibers innervating thoracic cavity structures form bundles or sympathetic nerves

© 2011 Pearson Education, Inc.Figure 14.3

The innervation of the sympathetic division: at left, thedistribution of nerves to the skin, skeletal muscles, andtissues of the body wall; at right, the distribution of nerves to visceral organs

PONS

Eye

Salivaryglands

Heart

Lung

Liver andgallbladder

Stomach

Spleen

Pancreas

Largeintestine

Smallintestine

Adrenalmedulla

Kidney

Urinary bladderScrotum

PenisUterus

Ovary

Inferiormesentericganglion

Superior mesentericganglion

Celiac ganglion

Cardiac andpulmonary plexuses

Sympathetic nerves

Splanchnicnerves(SEE NOTE 2)

T1T1

L2L2

Spinalcord

Superior

Middle

Inferior

Cervicalsympathetic

ganglia

Gray rami tospinal nerves(SEE NOTE 1)

Postganglionic fibers tospinal nerves (innervatingskin, blood vessels, sweatglands, arrector pilimuscles, adipose tissue)

Sympatheticchain ganglia

Coccygealganglia (Co1)

fused togetherNOTE 1

NOTE 2Every spinal nerve has a gray ramus thatcarries sympathetic postganglionic fibersfor distribution in the body wall and limbs.In the head and neck, postganglionicsympathetic fibers leaving the superiorcervical sympathetic ganglia supply theregions innervated by cranial nerves III,VII, IX, and X.

Preganglionic fibers on their way to the collateralganglia form the splanchnic (SPLANK-nik) nerves.Postganglionic fibers innervating structures in thethoracic cavity, such as the heart and lungs, formbundles known as sympathetic nerves. Preganglionic neurons

KEY

Ganglionic neurons


Module 14.3: Autonomic innervation patterns


• Vagus nerve (X) alone provides ~75% of all parasympathetic outflow

• Numerous vagus nerve branches intermingle with sympathetic fibers forming nerve plexuses

• Preganglionic fibers in sacral spinal cord segments form distinct pelvic nerves

• Innervate intramural ganglia in kidneys, bladder, terminal portions of large intestine, and sex organs

© 2011 Pearson Education, Inc.Figure 14.3

Preganglionicfibers in thesacral segmentsof the spinal cord,which carry sacralparasympatheticoutput

Spinalcord

S2

S3

S4

Uterus Ovary

Penis

Scrotum

Liver andgallbladder

Stomach

Spleen

Pancreas

Largeintestine

Smallintestine

Kidney

Urinary bladder

Rectum

Eye

Salivary glands

Heart

Lungs

Hypogastricplexus

Inferior mesentericplexus

Celiac plexus

Cardiac plexus

Vagus nerve (X),which providesabout 75 percentof all parasympa-thetic outflow

PONS

Otic ganglion

Submandibularganglion

Ciliary ganglion

Pterygopalatine ganglion

IIIVII

IX

The innervation of the parasympathetic division onone side of the body; the innervation on the oppositeside (not shown) follows the same pattern

Lacrimal gland

Preganglionic neuronsKEY

Ganglionic neurons


Module 14.3 Review

a. Define splanchnic nerves.

b. Which nerve carries the majority of the parasympathetic outflow?

c. Describe sympathetic nerves.


Module 14.4: Autonomic neurotransmitters and receptors

• Autonomic neurotransmitters and receptors


• Adrenergic receptors (bind “adrenaline”)

• Located in plasma membranes of target cells

• Binding of epinephrine (E) or norepinephrine (NE) activates enzymes (2nd messenger system) within cell

• Two classes

1. Alpha receptors (generally stimulated by NE & E)

• α1 receptors – generally excitatory

• α2 receptors – generally inhibitory




• Adrenergic receptors (continued)

• Two classes (continued)

2. Beta receptors (generally stimulated by E)

• β1 receptors – cardiac muscle stimulation and increased tissue metabolism

• β2 receptors – relaxation of respiratory passage and blood vessel smooth muscle

• β3 receptors – release of fatty acids from adipose tissue for metabolic use in other tissues




• Neurotransmitter release

• Epinephrine (E) and norepinephrine (NE) can be released

• Locally, involving more norepinephrine

• Effects last a few seconds

• Generally, from adrenal medulla

• 3× more epinephrine than norepinephrine

• More beta receptors activated

• Effects may last several minutes

© 2011 Pearson Education, Inc.Figure 14.4 1 – 2

The effects of sympathetic stimulation, which result primarily from the interactions of NE and E with adrenergicreceptors in the target cell’s plasma membrane

The stimulation of alpha receptors bynorepinephrine, which activates enzymeson the inside of the target cell’s plasmamembrane

The stimulation of beta receptors by epinephrine, which triggerschanges in the metabolic activity of the target cell

Epinephrine

Betareceptor

Activation ofadenylate cyclase

cAMP ATP

If β3

receptorIf β2 receptorIf β1

receptor

Cardiac musclestimulationand increasedtissuemetabolism

Relaxation of smoothmuscle in respiratorypassages and in theblood vessels of skeletalmuscle

Release of fattyacids by adiposetissue for metabolicuse in other tissues

CYTOPLASM OF TARGET CELLCYTOPLASM OF TARGET CELL

Gland cellsecretion

Smooth musclecontraction

Inhibition ofcell

Release of Ca2+

from ER

Reduction ofcAMP levels

Second messengersactivated

If α1

receptorIf α2

receptor

Plasma membraneAlpha

receptor

Norepinephrine




• Receptors (all bind ACh)

1. Nicotinic receptors (also bind nicotine)• Located on ganglion cell surfaces

• Also on sympathetic ganglion cells and at SNS neuromuscular junctions

• Always excitatory

2. Muscarinic receptors (also bind muscarine toxin)• Located at cholinergic neuromuscular and neuroglandular

junctions as well as some sympathetic cholinergic junctions

• Can be excitatory or inhibitory


CYTOPLASM OF TARGET CELL

The action of nicotinicreceptors of theparasympathetic division

AChNa+

Nicotinicreceptor

ACh

The action of muscarinic receptorsof the parasympathetic division

CYTOPLASM OF TARGET CELL

Muscarinicreceptor

G protein(inactive)

G proteinactivated

Plasma membrane

Metaboliceffects

Activation/inactivationof specific enzymes

The effects of the binding of ACh to nicotinic and muscarinic receptors of the parasympathetic division


Module 14.4 Review

a. Compare and contrast alpha and beta receptors.

b. Compare nicotinic receptors with muscarinic receptors.

c. An individual with high blood pressure (hypertension) is prescribed a drug that blocks beta receptors. How could this medication alleviate hypertension?


Module 14.5: Anatomical and physiological characteristics of ANS divisions

• Characteristics of ANS divisions

• Sympathetic activation

• Can occur at:

• Local level using mainly NE

• Affect only target organs

• Generalized body using E and NE

• Have effects in many organs

• Also alters CNS activity

• Controlled by hypothalamus



• Sympathetic activation effects

• Increased alertness through reticular activating system

• Feeling of energy and euphoria

• Increased activity in cardiovascular and respiratory centers of pons and medulla oblongata

• Increased blood pressure, heart/breathing rate, inspiration depth

• General elevation in muscle tone

• Mobilization of energy reserves

• Breakdown of liver and muscle glycogen

• Release of adipose tissue lipids



• Parasympathetic activation

• Under normal conditions, not controlled or activated as a whole

• Active continuously as individual reflex responses

• Effects center on relaxation, food processing, and energy absorption

• Also called anabolic division (anabole, a rising up) because blood nutrients generally increase



• Parasympathetic activation effects

• Constrictions of pupils and focusing of eye lenses for nearby objects

• Secretion of digestive glands

• Secretion of hormones that promote nutrient absorption and utilization

• Blood flow and glandular activity changes associated with sexual arousal



• Parasympathetic activation effects (continued)

• Increased digestive organ smooth muscle activity

• Stimulation and coordination of defecation

• Contraction of urinary bladder during urination

• Constriction of respiratory passageways

• Reduction in heart rate and force of contraction


A summary of the anatomical characteristics of the sympathetic divisionof the ANS (left) and of the parasympathetic division of the ANS (right)

A summary of the anatomical characteristics of the sympathetic division of the ANS

A summary of the anatomical characteristicsof the parasympathetic division of the ANS

Sympathetic

CNS CNS

PNS PNS

Adrenalmedulla

Bloodstream

Preganglionicneuron

Preganglionicneuron

Preganglionicfiber

Preganglionicfiber

Sympatheticganglion

Ganglionicneurons

Ganglionicneurons

Postganglionicfiber

Postganglionicfiber

Parasympatheticganglion

KEY

Neurotransmitters

Acetylcholne

Norepinephrine

EpinephrineTARGET TARGET

Parasympathetic

or


Module 14.5 Review

a. What neurotransmitter is released by all parasympathetic neurons?

b. Why is the parasympathetic division called the anabolic system?

c. What physiological changes are typical in tense (anxious) individuals?


Section 2: Autonomic Regulation and Control Mechanisms


• 14.6 Discuss the relationship between the two divisions of the ANS and the significance of

dual innervation.

• 14.7 Define a visceral reflex, and explain the significance of such reflexes.

• 14.8 Explain the roles of baroreceptors and chemoreceptors in homeostasis.

• 14.9 Describe the hierarchy of interacting levels of control in the autonomic nervous

system beginning with the hypothalamus.


Section 2: Autonomic Regulation and Control Mechanisms

• Autonomic Regulation and Control Mechanisms

• ANS output affects virtually every body system

• Unconscious ANS control can maintain homeostasis and vital physiological processes without conscious input

• Survival in a coma can continue for decades

© 2011 Pearson Education, Inc.Figure 14 Section 2

A general overview of theway the nervous systemdistributes information andissues motor commands

Central nervoussystem (CNS)processing

Processing at the consciouslevel, which can be affected bymemory, learning, or planning.

Sensory processingcenters

Motor centers operatingat the subconscious level.

Motor Responses

Motor pathways

Somatic Visceral

Sensory pathways

General sensoryreceptorsStimulus

Somatic nervoussystem (SNS)

Somatic effectors(skeletal muscles)

Autonomic nervoussystem (ANS)

Visceral effectors(smooth muscle,glands, cardiacmuscle, adipocytes)


Module 14.6: Visceral responses to ANS control

• Visceral responses to ANS control

• Even in the absence of stimuli, autonomic motor neurons maintain continuous activity

• = Autonomic tone

• Many organs receive signals from both ANS divisions

• = Dual innervation

• Effects may be opposing or complementary

• In organs with only sympathetic innervation, response may vary with receptor type







Module 14.6: Visceral responses to ANS control

• Dual innervation example: heart

• Heart consists of cardiac muscle tissue triggered by specialized pacemaker cells affected by ANS

• Parasympathetic: ACh release decreases heart rate

• Sympathetic: NE release accelerates heart rate

• Small amounts of both neurotransmitters released continuously to maintain autonomic tone

• Under resting conditions, parasympathetic dominates


At rest, both ANSdivisions are activeat low levels, butparasympatheticeffects predominate.

Increasedparasympatheticstimulationlowers theheart rate.

Parasympatheticinhibition or sympatheticstimulation increases theheart rate. The balancebetween these factorscan be precisely adjusted.

Increased sympatheticstimulation combinedwith parasympatheticinhibition result in anincrease in heart rate tomaximum levels.

Time

180

120

72

50

He

art

ra

te(b

ea

ts p

er

min

ute

)

The effects of both autonomic divisions on the heart, which receives dual innervation


Module 14.6 Review

a. Define dual innervation.

b. Discuss autonomic tone and its significance in controlling visceral function.

c. You go outside in winter and blood flow to your skin is reduced, conserving body heat. You become angry, and your face turns red. Explain these changes.


Module 14.7: Visceral reflexes

• Visceral reflexes

• Provide automatic motor responses that can be modified, facilitated, or inhibited by higher centers (especially those of hypothalamus)

• All are polysynaptic

• Components of reflex arc

1. Receptor (interoceptors such as nociceptors, thermoreceptors, baroreceptors, chemoreceptors, etc.)

2. Sensory neuron

3. Processing center (spinal cord nuclei and solitary nuclei of brain stem)

4. Visceral motor neurons (one or two)



• Two visceral reflex types

1. Short reflexes

• Bypass CNS entirely

• Impulses relay with interneurons in ganglia

• Control simple motor responses with localized effects

• Usually just one part of an organ

• Predominate in enteric nervous system


A short reflex, which bypasses the CNS and involvessensory neurons and interneurons whose cell bodies arelocated within autonomic ganglia

Stimulus

Receptors inperipheral tissue

Afferent(sensory) fibers

Autonomicganglion

Ganglionicneuron

Shortreflex

Peripheraleffector

Response



• Two visceral reflex types (continued)

2. Long reflexes

• Pathway

• Visceral sensory neurons in cranial nerves and autonomic nerves enter CNS through dorsal roots

• Interneurons process information in CNS

• ANS motor neurons carry response to visceral effectors

• Predominate over short reflexes

• Activate entire organs and coordinate responses of multiple organ systems

Animation: Sympathetic Innervation

Animation: Parasympathetic Innervation


A long reflex, which is the autonomic equivalentof a polysynaptic reflex

Stimulus

Receptors inperipheral tissue

Longreflex

Central nervoussystem

Processing centerin spinal cord

(or brain)

Preganglionicneuron

Autonomicganglion

PeripheraleffectorResponse




Module 14.7 Review

a. Define visceral reflex.

b. Describe the solitary nucleus.

c. Compare short reflexes with long reflexes.


Module 14.8: Monitoring visceral function with baroreceptors and chemoreceptors

• Baroreceptors

• Stretch receptors that monitor pressure changes

• Distortion of dendritic branches changes AP generation rate

• Free nerve endings in walls of:

• Blood vessels (monitor blood pressure and flow)

• Tubes of respiratory, digestive, and urinary tracts (monitor volume changes)


The sites and functions of thebody’s baroreceptors

Baroreceptors of CarotidSinus and Aortic Sinus

Baroreceptors of Lungs

Baroreceptors of Colon

Baroreceptors of Digestive Tract

Baroreceptors of Bladder Wall

Provide information onvolume of tract segments,trigger reflex movement ofmaterials along tract

Provide information on volume of urinarybladder, trigger urinationreflex

Provide information on volumeof fecal material in colon, triggerdefecation reflex

Provide information on lungstretching to respiratoryrhythmicity centers for controlof respiratory rate

Provide information on bloodpressure to cardiovascular andrespiratory control centers


Module 14.8: Monitoring visceral function with baroreceptors and chemoreceptors

• Chemoreceptors

• Specialized neurons detecting small changes in specific chemical or compound concentration

• Reflexive control of respiratory and cardiovascular function

• Are found in:

1. Medulla oblongata and other brain areas

• Monitor pH and PCO2 in CSF

2. Carotid bodies (near origin of internal carotid arteries in neck)

• Monitor pH, PCO2, and PO2 in blood

3. Aortic bodies (between branches of aortic arch)

• Monitor pH, PCO2, and PO2 in blood


Chemoreceptors of Aortic Bodies

Chemoreceptors of Carotid Bodies

Chemoreceptors in RespiratoryCenters in the Medulla Oblongata

The body’s chemoreceptors, which play important roles in thereflexive control of respiration and cardiovascular function

Sensitive to changes in the pH,PCO2

, and PO2 in arterial blood

Sensitive to changes in the pH,PCO2

, and PO2 in arterial blood

Respond to the concentrations ofhydrogen ions (pH) and carbondioxide (PCO2

) in cerebrospinal fluid

Via cranialnerve IX

Via cranialnerve X

Trigger reflexiveadjustments inrespiratory andcardiovascularactivity

Trigger reflexiveadjustments indepth and rate ofrespiration


Blood vessel

Chemoreceptiveneurons

A photomicrograph ofa carotid body

Carotid body LM x 400

The body’s chemoreceptors, which play important roles in thereflexive control of respiration and cardiovascular function


Module 14.8 Review

a. Define baroreceptor and chemoreceptor.

b. Which type of receptor is sensitive to changes in blood pH?

c. Where are baroreceptors located within the body?


Module 14.9: Levels of ANS motor control

• Autonomic activities are controlled mainly in two CNS areas

1. Autonomic ganglia and spinal cord

• Simple reflexes

2. Medulla oblongata

• More complex reflexes

• Cardiovascular reflexes

• Respiratory reflexes

• Salivation

• Swallowing digestive secretions

• Peristalsis

• Urinary function


Module 14.9: Levels of ANS motor control

• Lower CNS centers are subject to regulation by higher brain areas

• Hypothalamus

• Limbic system

• Thalamus

• Cerebral cortex


Module 14.9 Review

a. What structure within the brain relays sensory information?

b. Identify the target structures for the SNS and ANS.

c. Harry has a brain tumor that is pressing against his hypothalamus. Would you expect this tumor to interfere with autonomic function? Why or why not?

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14 The Autonomic Nervous System