The Nervous System: Autonomic Nervous...

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17 The Nervous System:

Autonomic Nervous

System


Introduction

•The autonomic nervous system:

• Functions outside of our conscious awareness

• Makes routine adjustments in our body’s

systems

•The autonomic nervous system:

• Regulates body temperature

• Coordinates cardiovascular, respiratory,

digestive, excretory, and reproductive

functions


Subdivisions of the ANS

• The autonomic nervous

system consists of

two major subdivisions

• Sympathetic division

• Also called the

thoracolumbar division

• Known as the “fight or

flight” system

• Parasympathetic division

• Also called the

craniosacral division

• Known as the “rest and

digest” system


A Comparison of the Somatic and

Autonomic Nervous Systems • The autonomic nervous system differs from

the somatic nervous system in the arrangement of the neurons connecting the central nervous system to the effector organs.

• Visceral motor neurons in the CNS, known as preganglionic neurons, send their axons, called preganglionic fibers, to synapse on ganglionic neurons, whose cell bodies are located outside the CNS, in autonomic ganglia.

• Axons from the ganglionic neurons are called postganglionic fibers because they carry impulses away from the ganglion.

• Postganglionic fibers innervate peripheral tissues and organs, such as cardiac and smooth muscle, adipose tissue, and glands.


Subdivisions of the ANS

•Sympathetic division

• Thoracic and upper lumbar nerves synapse in

ganglia near the spinal cord

• Sympathetic activation results in:

• Increased metabolism and alertness

•Parasympathetic division

• Synapses are located near the target organ

• Parasympathetic activation results in:

• Energy conservation


The Sympathetic Division

•Sympathetic division consists of:

• Preganglionic neurons between T1 and L2

• Two types of ganglionic neurons near the

vertebral columns:

sympathetic chain ganglia also called

paravertebral ganglia

collateral ganglia also known as prevertebral

ganglia

• Specialized neurons in the interior of the

suprarenal gland


Figure 17.2 Organization of the Sympathetic Division of the ANS

Preganglionic fibers

Postganglionic fibers

Hormones released

into circulation

KEY

Lateral gray

horns of spinal

segments

T1–L2

Sympathetic

chain ganglia

(paired)

Collateral

ganglia

(unpaired)

Suprarenal

medullae

(paired)

Preganglionic Neurons

Ganglionic Neurons

Innervation by

postganglionic

fibers

Through release of

hormones into

the circulation

Target Organs

Visceral effectors

in thoracic cavity,

head, body wall,

and limbs

Visceral effectors

in abdominopelvic

cavity

Organs and systems

throughout body

Sympathetic Division of ANS


Sympathetic division of the ANS

• Sympathetic division

• All preganglionic fibers

release acetylcholine

(Ach)

• Most postganglionic

fibers release

norepinephrine

(adrenergic)

stimulatory effects



• Effects of Sympathetic Chain

Ganglia

• Reduction of circulation to the

skin

• More circulation to skeletal

muscles

• Stimulates more energy

production by skeletal muscles

• Releases stored adipose

• Stimulation of arrector pili

muscles

• Dilation of pupils

• Increased heart rate

• Dilation of respiratory tubes



•Summary of the Sympathetic Division

• Consists of parallel chains on either side of the

spinal cord

• Preganglionic fibers are short and extend

from the spinal cord to the sympathetic chain

• Postganglionic fibers are long and extend

from the spinal cord to the body organs

• All preganglionic neurons release Ach

• Most postganglionic neurons release

norepinephrine


Figure 17.4 Anatomical Distribution of Sympathetic Postganglionic Fibers

Superior

Middle

Inferior

PONS

Cervical

sympathetic

ganglia

Gray rami to

spinal nerves

Greater

splanchnic

nerve

Superior

mesenteric

ganglion

Cardiac and

pulmonary

plexuses

Celiac ganglion

Sympathetic nerves

T1 T1

T2 T2

T3 T3

T4 T4

T5 T5

T6 T6

T7 T7

T8 T8

T9 T9

T10 T10

T11 T11

T12 T12

L1 L1

L2 L2

L3 L3

L4 L4

L5 L5 S1 S1 S2 S2

S3 S3 S4 S4

S5 S5

Postganglionic fibers

to spinal nerves

(innervating skin, blood

vessels, sweat glands,

arrector pili muscles,

adipose tissue)

Sympathetic

chain ganglia

Spinal cord

Coccygeal

ganglia (Co1)

fused together

(ganglion impar)

Preganglionic neurons

Ganglionic neurons

KEY

Uterus Ovary

Sacral

splanchnic

nerves

Lesser

splanchnic

nerve

Lumbar

splanchnic nerves Inferior

mesenteric

ganglion

Penis Scrotum Urinary bladder

Kidney

Suprarenal

medulla

Small intestine

Large intestine

Pancreas

Spleen

Stomach

Liver and

gallbladder

Lung

Heart

Eye

Salivary

glands


The Parasympathetic Division

•Parasympathetic Division

• Preganglionic neurons are in the brain stem and

sacral segments

• Parasympathetic division is more localized and

specific as compared to the sympathetic division

• Postganglionic neurons are near (terminal) the

target organ or within (intramural) the target

organ


Parasympathetic division of the ANS

• Parasympathetic

division

• All preganglionic fibers


• Postganglionic fibers


(cholinergic)

inhibitory effects


The Parasympathetic Division

• Effects of the Parasympathetic Division

• Pupil constriction

• Secretion of digestive enzymes from digestive glands

• Increased smooth muscle activity of the digestive

system

• Stimulation and coordination of defecation

• Contraction of the urinary bladder

• Constriction of respiratory passages

• Reduced heart rate

• Sexual arousal


Figure 17.8 Autonomic Distribution of the Parasympathetic Output Pterygopalatine ganglion

PONS

N III

N VII

N IX

N X (Vagus)

Ciliary ganglion

Submandibular

ganglion

Otic ganglion

Autonomic plexuses

(see Figure 17.9)

Pelvic

nerves

Lacrimal gland

Eye

Salivary glands

Heart

Lungs

Liver and

gallbladder

Stomach

Spleen

Pancreas

Large intestine

Small intestine

Rectum

Kidney

Urinary bladder Scrotum Penis Ovary Uterus

S2

S3

S4

Spinal

cord

Preganglionic neurons

Ganglionic neurons

KEY


Relationships between the Sympathetic and

Parasympathetic Divisions

•Sympathetic

• Widespread stimulatory effect on visceral organs

•Parasympathetic

• Modifies/inhibits the activity of structures innervated by specific cranial nerves and pelvic nerves

•Most vital organs are innervated by both the sympathetic and parasympathetic nerves

• The two often oppose (antagonistic) each other


Figure 17.10 A Comparison of the Sympathetic and Parasympathetic Divisions

Sympathetic Parasympathetic

CNS

PNS

KEY

Sympathetic

ganglion

Circulatory

system

Preganglionic

neuron

Preganglionic

fiber

Ganglionic

neurons

Postganglionic

fiber

TARGET

Parasympathetic

ganglion

Neurotransmitters

Acetylcholine

Norepinephrine

Epinephrine or


Relationships between the Sympathetic and

Parasympathetic Divisions

• Dual Innervation • The parasympathetic

fibers accompany the

sympathetic fibers to

the target organ

• The parasympathetic

and sympathetic fibers

mingle together forming

peripheral autonomic

plexuses


Visceral Reflexes

•All are polysynaptic

•Reflexes can be:

• Long reflexes

• Short reflexes


Visceral Reflexes

•Long Reflexes

• Visceral sensory

neurons go to the CNS

via the dorsal roots

• There are interneurons

within the CNS

• Information is

“interpreted” in the

spinal cord or brain

• ANS sends motor

commands to the

visceral organs


Visceral Reflexes

• Short Reflexes

• Sensory nerve

impulses go to the

ganglionic neurons

• Motor commands are

distributed by the

postganglionic fibers

• Impulses bypass the

CNS


Levels of Somatic Motor Control

•Summary of somatic motor control

• Thalamus

• Controls reflexes associated with visual and

auditory stimuli

• Hypothalamus

• Responds to hunger, thirst, and sexual activity

• Pons

• Regulates the rhythmic breathing patterns


Levels of Somatic Motor Control

•Summary of somatic motor control

• Medulla oblongata

• Alters the breathing patterns

• Brain stem

• Controls simple reflexes

• Spinal cord

• Controls simple reflexes

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