ANSWER THE ESSAYS AND THE BULLET (-) QUESTIONS

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Autonomic Nervous System

Autonomic Nervous System & Visceral Reflexes

Autonomic Nervous System (ANS)
general properties
anatomy

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

Walter Cannon- coined the expressions as homeostasis & fight or flight

homeostasis cannot be maintained without the ANS

General Properties of ANS

autonomic nervous system (ANS) – motor nervous system controlling glands, cardiac & smooth muscle

a.k.a. visceral motor system
primary organs of ANS
viscera of thoracic and abdominal cavities
some structures of the body wall
cutaneous blood vessels
sweat glands
piloerector muscles
involuntarily – w/o conscious intent
visceral effectors function modulated by ANS

Visceral Reflexes

visceral reflexes – unconscious & automatic responses, slower

visceral reflex arc
receptors – nerve endings that detect stretch, tissue damage, blood chemicals, body temperature, & 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

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

example of homeostatic negative feedback loop

Glossopharyngeal

nerve transmits signals

to medulla oblongata

Baroreceptors

sense increased

blood pressure

Common carotid

artery

Vagus nerve

transmits

inhibitory

signals

to cardiac

pacemaker

Terminal

ganglion

Heart rate

decreases

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
increases 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 according to the body’s changing needs
parasympathetic tone
maintains smooth muscle tone in intestines
holds resting heart rate down to ~ 70 – 80 beats / min
sympathetic tone
keeps most blood vessels partially constricted and maintains blood pressure

sympathetic division excites the hearts but inhibits digestive & urinary function, while parasympathetic has the opposite effect

Neural Pathways

ANS has components in both the central & peripheral nervous systems
control nucleus in hypothalamus and other brainstem regions
motor neurons in the spinal cord & peripheral ganglia
nerve fibers that travel through the cranial & spinal nerves

somatic motor pathway
a motor neuron from the brainstem or spinal cord issues a myelinated axon that reaches all the way to the skeletal muscle

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 – the first neuron has a soma in the brainstem or spinal cord
synapses with a postganglionic neuron whose axon extends the rest of the way to the target cell

Somatic versus Autonomic Pathways

ANS – two neurons from CNS to effectors

presynaptic neuron whose cell body is in CNS
postsynaptic neuron cell body in peripheral ganglion

Somatic efferent innervation

Autonomic efferent innervation

ACh

ACh or NE

Myelinated

fiber

Somatic effectors

(skeletal muscles)

Myelinated

preganglionic fiber

Unmyelinated

postganglionic fiber

Autonomic

ganglion

Visceral effectors

(cardiac muscle,

smooth muscle,

glands)

a.k.a. thoracolumbar division because it arises from the thoracic & lumbar regions of spinal cord

relatively short preganglionic and long postganglionic fibers

preganglionic neurosomas in lateral horns & nearby regions of the gray matter of spinal cord
fibers exit spinal cord by way of spinal nerves T1 to L2
lead to nearby sympathetic chain of ganglia (paravertebral ganglia)
series of longitudinal ganglia adjacent to both sides of the vertebral column from cervical to coccygeal levels
usually 3 cervical, 11 thoracic, 4 lumbar, 4 sacral, and 1 coccygeal ganglion
sympathetic nerve fibers are distributed to every level of the body

Sympathetic Nervous System

each paravertebral ganglion is connected to a spinal nerve by two branches – communicating rami

preganglionic fibers are small myelinated fibers that travel form spinal nerve to the ganglion by way of the white communicating ramus (myelinated)

postganglionic fibers leave the ganglion by way of the gray communicating ramus (unmyelinated)
forms a bridge back to the spinal nerve

postganglionic fibers extend the rest of the way to the target organ

Sympathetic Nervous System

Sympathetic Chain Ganglia

Cardiac n.

Splanchnic n.

Heart

Rib

Bronchi

Diaphragm

Phrenic n.

Superior

vena cava

Vagus n.

Sympathetic

chain

Communicating

ramus

Thoracic

ganglion

after entering the sympathetic chain, the postganglionic fibers may follow any of three courses

end in ganglia & synapse w/ postganglionic neuron

travel along chain & synapse in ganglia at other levels
these fibers link the paravertebral ganglia into chain
only route ganglia at cervical, sacral, & coccygeal levels receive input

pass through chain w/o synapsing & continue as splanchnic nerves

Sympathetic Nervous System

nerve fibers exit sympathetic chain by
spinal nerve route
most sweat glands, piloerector muscles, & blood vessels of the skin & skeletal muscles

sympathetic nerve route
nerves extend to the heart, lungs, esophagus & thoracic blood vessels
nerves form carotid plexus around carotid artery
issue fibers to effectors in the head (salivary, nasal glands, iris dilators)
cervical ganglia form cardiac nerves to heart

splanchnic nerve route
fibers arise from spinal nerves T5 to T12 pass through the sympathetic ganglia w/o synapsing
continue on as the splanchnic nerves
lead to second set of ganglia – collateral (prevertebral) ganglia and synapse there

Sympathetic Nervous System

collateral ganglia form network- abdominal aortic plexus

wraps around abdominal aorta

three major collateral ganglia in this plexus
celiac, superior mesenteric, and inferior mesenteric
postganglionic fibers accompany these arteries & their branches to their target organs

solar plexus – collective name for the celiac and superior mesenteric ganglia
nerves radiate from ganglia like rays of the sun

Sympathetic Nervous System

Efferent Pathways

Salivary glands

Heart

Lung

Stomach

Spleen

Pancreas

Small intestine

Large intestine

Rectum

Kidney

Bladder

Penis

Scrotum

Uterus

Ovary

Pons

Regions of spinal cord

Thoracic

Cervical

Lumbar

Sacral

Eye

Adrenal medulla

Preganglionic neurons

Postganglionic neurons

Postganglionic fibers to

skin, blood vessels,

adipose tissue

Sympathetic chain

ganglia

Liver and

gallbladder

Inferior

mesenteric

ganglion

Superior

mesenteric

ganglion

Celiac

ganglion

Cardiac and

pulmonary plexuses

Preganglionic Pathways

Collateral ganglion

Spinal nerve

White ramus

Gray ramus

Sympathetic nerve

Splanchnic nerve

Postganglionic neuron

Preganglionic neuron

Somatic neuron

Somatic

motor fiber

To somatic effector

(skeletal muscle)

Soma of

somatic motor

neuron

Postganglionic

sympathetic fibers

To liver, spleen, adrenal glands,

stomach, intestines, kidneys,

urinary bladder, reproductive organs

Sympathetic

ganglion

Sympathetic

trunk

Soma of

postganglionic

neuron

Communicating

rami

Postganglionic

sympathetic fiber

Preganglionic

sympathetic fiber

Soma of

preganglionic

neuron

To sweat glands,

piloerector muscles,

and blood vessels

of skin and

skeletal muscles

To iris, salivary glands,

lungs, heart, thoracic

blood vessels, esophagus

15-*

Ganglia and Abdominal Aortic Plexus

Celiac ganglia

(a)

(b)

Aortic plexus

Renal plexus

Esophagus

Diaphragm

Kidney

Superior mesenteric artery

Inferior mesenteric artery

Aorta

Celiac trunk

Adrenal gland

Adrenal cortex

Adrenal medulla

First lumbar

sympathetic

ganglion

Pelvic

sympathetic

chain

Inferior mesenteric

ganglion

Superior mesenteric

ganglion

Figure 15.6

Summary of Sympathetic Innervation

effectors in body wall are innervated by sympathetic fibers in spinal nerves

effectors in head and thoracic cavity are innervated by fibers in sympathetic nerves

effectors in abdominal cavity are innervated by sympathetic fibers in splanchnic nerves

Adrenal Glands

paired adrenal glands on superior poles of the kidneys

each is two glands with different functions
adrenal cortex (outer layer)- secretes steroid hormones

adrenal medulla (inner core)- a sympathetic ganglion
modified postganglionic neurons w/o dendrites or axons
stimulated by preganglionic sympathetic neurons that terminate on these cells
secretes hormones into bloodstream
catecholamines - 85% epinephrine (adrenaline) and 15% norepinephrine (noradrenaline)
also function as neurotransmitters

Parasympathetic Division

parasympathetic division is also called the craniosacral division
arises from the brain and sacral regions of the spinal cord
fibers travel in certain cranial and sacral nerves

origin of long preganglionic neurons
midbrain, pons, and medulla
sacral spinal cord segments S2-S4

pathways of long preganglionic fibers
fibers in cranial nerves III, VII, IX and X
fibers arising from sacral spinal cord
pelvic splanchnic nerves and inferior hypogastric plexus

terminal ganglia in or near target organs
long preganglionic, short postganglionic fibers

Parasympathetic Cranial Nerves

Oculomotor nerve (III)
narrows pupil and focuses lens

Facial nerve (VII)
tear, nasal and salivary glands

Glossopharyngeal nerve (IX)
parotid salivary gland

Vagus nerve (X)
viscera as far as proximal half of colon
cardiac, pulmonary, and esophageal plexus

Lacrimal gland

Heart

Lung

Stomach

Pancreas

Small intestine

Rectum

Bladder

Penis

Scrotum

Uterus

Ovary

Ciliary ganglion

Spleen

Descending

colon

Otic ganglion

Cardiac plexus

Eye

Thoracic

Cervical

Lumbar

Sacral

Preganglionic neurons

Postganglionic neurons

Pterygopalatine

ganglion

Oculomotor n.

(CN III)

Submandibular

ganglion

Facial n.

(CN VII)

Submandibular

salivary gland

Parotid

salivary gland

Glossopharyngeal n.

(CN IX)

Vagus n.

(CN X)

Pulmonary

plexus

Esophageal

plexus

Abdominal

aortic

plexus

Pelvic

splanchnic

nerves

Inferior

hypogastric

plexus

Liver and

gallbladder

Kidney and

ureter

Transverse

colon

Pelvic

nerves

Regions of

spinal cord

Celiac

ganglion

Efferent Pathways

remaining parasympathetic fibers arise from levels S2 to S4 of the spinal cord

form pelvic splanchnic nerves that lead to the inferior hypogastric plexus

most form pelvic nerves to their terminal ganglion on the target organs
distal half of colon, rectum, urinary bladder, and reproductive organs

Lacrimal gland

Heart

Lung

Stomach

Pancreas

Small intestine

Rectum

Bladder

Penis

Scrotum

Uterus

Ovary

Ciliary ganglion

Spleen

Descending

colon

Otic ganglion

Cardiac plexus

Eye

Thoracic

Cervical

Lumbar

Sacral

Preganglionic neurons

Postganglionic neurons

Pterygopalatine

ganglion

Oculomotor n.

(CN III)

Submandibular

ganglion

Facial n.

(CN VII)

Submandibular

salivary gland

Parotid

salivary gland

Glossopharyngeal n.

(CN IX)

Vagus n.

(CN X)

Pulmonary

plexus

Esophageal

plexus

Celiac

ganglion

Abdominal

aortic

plexus

Pelvic

splanchnic

nerves

Inferior

hypogastric

plexus

Liver and

gallbladder

Kidney and

ureter

Transverse

colon

Pelvic

nerves

Regions of

spinal cord

Neurotransmitters and Receptors

Mechanism of differential effects of autonomic neurons

constricting some vessels but dilating others

neurotransmitters released and receptor types found on target cells

2 fundamental reasons:

sympathetic & parasympathetic fibers secrete different neurotransmitters

target cells respond to same neurotransmitter differently depending on the receptor type
all autonomic fibers secrete either acetylcholine or norepinephrine
2 classes of receptors for each of these neurotransmitters

Acetylcholine (ACh)

ACh secreted by all preganglionic neurons in both divisions & the postganglionic parasympathetic neurons (cholinergic fibers)

2 types of cholinergic receptors
muscarinic receptors
all cardiac & smooth muscle, & gland cells have muscarinic receptors
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
called adrenergic fibers
receptors for it called adrenergic receptors

alpha-adrenergic receptors
usually excitatory
2 subclasses use different 2nd messengers (α1 & α2)

beta-adrenergic receptors
usually inhibitory
2 subclasses with different effects, but both act through cAMP as a second messenger (β1 & β2)

Overview

autonomic effects on glandular secretion are often indirect result of effect on blood vessels
vasodilation – increased blood flow – increased secretion
vasoconstriction – decreased blood flow – decreased secretion

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

Dual Innervation

dual innervation - most viscera receive nerve fibers from both parasympathetic &

sympathetic divisions

antagonistic effect – 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

cooperative effects – two divisions act on different effectors to produce a unified overall effect
parasympathetics increase salivary serous cell secretion
sympathetics increase salivary mucous cell secretion

Dual Innervation of the Iris

Brain

Spinal cord

Iris

Pupil

Pupil dilated

Pupil constricted

Parasympathetic fibers

of oculomotor nerve (III)

Sympathetic

fibers

Ciliary

ganglion

Superior

cervical

ganglion

Parasympathetic

(cholinergic) effect

Sympathetic

(adrenergic) effect

Adrenergic

stimulation of

pupillary dilator

Cholinergic stimulation

of pupillary constrictor

Control of Autonomic Function

ANS regulated by several levels of CNS
cerebral cortex has an influence – anger, fear, anxiety

hypothalamus - major visceral motor control center
nuclei for primitive functions – hunger, thirst

midbrain, pons, and medulla oblongata contain:
nuclei for cardiac & vasomotor control, salivation, swallowing, sweating, bladder control, and pupillary changes

spinal cord reflexes
defecation and micturition reflexes- integrated in spinal cord

neuropharmacology – study of effects of drugs on the nervous system

sympathomimetics- enhance sympathetic activity
cold medicines dilate bronchioles or constrict nasal blood vessels

sympatholytics- suppress sympathetic activity
beta blockers reduce high BP interfering w/ effects of epinephrine/norepinephrine on heart & blood vessels

many drugs also act on neurotransmitters in CNS
Prozac blocks reuptake of serotonin to prolong its mood-elevating effect

caffeine competes with adenosine (the presence of which causes sleepiness) by binding to its receptors

Drugs and the Nervous System