Transcript Biosc_48_Chapter_9_lecture

Chapter 09
ANS
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I. Neural Control of Involuntary
Effectors
Autonomic Neurons
1. Innervate organs not under voluntary control
2. Effectors include:
a. Cardiac muscle
b. Smooth muscle of visceral organs and blood
vessels
c. Glands
3. Part of the PNS
Differences between somatic and autonomic


Somatic motor neurons have cell bodies in the
spinal cord and just one neuron traveling from
spinal cord to effector.
Autonomic motor system has two sets of
neurons in the PNS.
 The preganglionic neuron has cell bodies in
the brain or spinal cord and synapses in an
autonomic ganglion
 The postganglionic neuron has cell bodies in
the ganglion and synapses on the effector
Autonomic Neurons



Preganglionic neurons: originate in the
midbrain or hindbrain or from the thoracic,
lumbar, or sacral spinal cord
Postganglionic neurons: originate in ganglion
Autonomic ganglia are located in the head,
neck, and abdomen as well as in chains along
either side of the spinal cord
The ANS has pre- and postganglionic neurons
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Autonomic
ganglion
CNS
Involuntary
effector
Smooth
muscle
Preganglionic
neuron
Postganglionic
neuron
Visceral Effector Organs

Somewhat independent of innervation and will not
atrophy if a nerve is cut (unlike skeletal muscle)
 Target may become even more sensitive to
destimulation; called denervation
hypersensitivity
 Cardiac muscle and some smooth muscle
contract rhythmically without nerve stimulation.
Autonomic innervation can speed up or slow
down intrinsic contractions.
 Autonomic motor neurons can stimulate or inhibit,
depending on the organ and the receptors
Neurotransmitters


Somatic motor neurons release only acetylcholine
which is always excitatory.
Autonomic neurons release mainly acetylcholine
and norepinephrine but may be excitatory or
inhibitory
Somatic vs. Autonomic System
II. Divisions of the Autonomic
Nervous System
Sympathetic Division
1. Preganglionic neurons orginate from the thoracic
and lumbar regions of the spinal cord.
a. Also called the thoracolumbar division
2. Preganglionic neurons synapse in sympathetic
ganglia that run parallel to the spinal cord.
a. These are called the paravertebral ganglia.
b. These ganglia are connected, forming a
sympathetic chain of ganglia (sympathetic
trunk).
Sympathetic Division
3. Myelinated axons of the preganglionic neurons
exit the spinal cord at ventral roots and travel in
white rami communicantes and synapse in
autonomic ganglia at multiple levels.
4. Unmyelinated axons of the postganglionic
neurons form the gray rami communicantes,
which return to the spinal nerve and travel with
other spinal nerves to their effectors.
Sympathetic Chain of Paravertebral Ganglia
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Spinal cord
Posterior (dorsal) root
Anterior (ventral) root
Sympathetic chain of
paravertebral ganglia
Rami communicantes
Sympathetic ganglion
Spinal nerve
Vertebral body
Rib
Convergence and Divergence
a. Because preganglionic neurons can branch and
synapse in ganglia at any level, there is:
1) Divergence: One preganglionic neuron
synapses on several postganglionic neurons at
different levels.
2) Convergence: Several preganglionic neurons
at different levels synapse on one
postganglionic neuron.
b. Allows the sympathetic division to act as a single
unit through mass activation and to be tonically
active
Sympathetic Neuron Pathways
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Visceral effectors:
Smooth muscle of
blood vessels, arrector
pili muscles, and
sweat glands
1. Preganglionic axons
synapse with
postganglionic
neurons
Dorsal
root
2. Postganglionic
axons innervate
target organs
Sympathetic
chain
ganglion
Dorsal root
ganglion
Spinal
nerve
Sympathetic chain
White
ramus
Ventral
root
Splanchnic
nerve
Gray ramus
Visceral effector:
intestine
Collateral
ganglion
(celiac ganglion)
Spinal cord
Preganglionic neuron
Postganglionic neuron
Collateral Ganglia

Many of the sympathetic neurons that exit the
spinal cord below the diaphragm do not synapse
in the sympathetic chain of ganglia.
 Instead, they form splanchnic nerves, which
synapse in collateral ganglia.
1) Collateral ganglia include celiac, superior
mesenteric, and inferior mesenteric ganglia.
2) Postganglionic neurons innervate organs of the
digestive, urinary, and reproductive systems.
Collateral Sympathetic Ganglia
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Diaphragm
Superior mesenteric
ganglion
Celiac ganglion
Adrenal gland
Renal plexus
First lumbar
sympathetic
ganglion
Aortic plexus
Inferior mesenteric
ganglion
Pelvic sympathetic
chain
Adrenal Glands



The adrenal medulla secretes epinephrine and
norepinephrine when stimulated by the
sympathetic nervous system as a part of mass
activation
Chromaffin cells of the adrenal medulla are
modified postganglionic neurons that have lost
their axons
Preganglionic sympathetic neurons innervate
directly on these cells.
Summary of the Sympathetic Division
Parasympathetic Division

Preganglionic neurons originate from the
brainstem or sacral region of the spinal cord.
a. Also called the craniosacral division
b. They synapse on ganglia located near or in
effector organs; called terminal ganglia
c. Preganglionic neurons do not travel with
somatic neurons (as sympathetic
postganglionic neurons do).
 Terminal ganglia supply very short postganglionic
neurons to the effectors
Cranial Nerves and the Parasympathetic Division

The occulomotor, facial, glosso-pharyngeal, and
vagus nerves carry parasympathetic
preganglionic neurons.
 Occulomotor (III) nerve
1) Preganglionic fibers exit midbrain and synapse
on the ciliary ganglion.
2) Postganglionic fibers innervate the ciliary
muscle of the eye.
Cranial Nerves and the Parasympathetic Division

Facial (VII) nerve: Preganglionic fibers exit the
pons and synapse in:
1) Pterygopalatine ganglion: Postganglionic
fibers synapse on nasal mucosa, pharynx,
palate, and lacrimal glands.
2) Submandibular ganglion: Postganglionic
fibers synapse on salivary glands.
Cranial Nerves and the Parasympathetic Division

Glossopharyngeal (IX) nerve:
 Preganglionic fibers exit medulla and synapse
on otic ganglion. Postganglionic fibers
innervate the parotid gland.

Vagus (X) nerve:
 Preganglionic fibers exit medulla, branch into
several plexi and nerves, and travel to
terminal ganglia within effector organs (heart,
lungs, esophagus, stomach, pancreas, liver,
intestines).
Path of the Vagus Nerve
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Hyoid bone
Vagus nerve
Thyroid cartilage
of larynx
Trachea
Right
pulmonary
plexus
Right
cardiac
branch
Left pulmonary plexus
Right
gastric nerve
Left gastric nerve
Celiac plexus
Liver
Superior
mesenteric nerve
Left cardiac branch
Stomach
Sacral Nerves

Preganglionic nerves originate in lateral gray
horn of spinal cord segments S2,3,4 and
synapse on terminal ganglia

Postganglionic nerves provide innervation to the
descending colon, sigmoid colon, rectum, urinary
organs and reproductive organs.
Summary of Parasympathetic Division
Comparison of the Sympathetic and
Parasympathetic Divisions
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Cranial nerve III
Midbrain
Cranial nerve VII
Hindbrain
Cranial nerve IX
Ciliary muscle and
pupil of eye
Lacrimal gland
and nasal mucosa
Cranial nerve X
Submandibular
and sublingual
glands
T1
T2
T3
Parotid gland
T4
T5
Lung
T6
T7
T8
T9
Sympathetic chain
ganglion
Greater splanchnic
nerve
T12
Spleen
Lesser splanchnic
nerve
S2
S3
S4
Stomach
Pancreas
L1
L2
Heart
Liver and gallbladder
T10
T11
Celiac
ganglion
Superior
mesenteric
ganglion
Large intestine
Small intestine
Adrenal gland
and kidney
Inferior
mesenteric
ganglion
Urinary bladder
Pelvic nerves
Reproductive
organs
III. Functions of the
Autonomic Nervous System
General functions
Sympathetic Functions
 The sympathetic division activates the body for
“fight or flight” through the release of
norepinephrine from postganglionic neurons
and the secretion of epinephrine from the
adrenal medulla.
 Prepares the body for intense physical activity
in emergencies by increasing heart rate and
blood glucose levels and by diverting blood to
skeletal muscles
 Tonically regulates heart, blood vessels, and
other organs
General functions
Parasympathetic Functions
 The parasympathetic division is antagonistic to
the sympathetic division.
 Allows the body to “rest and digest” through
the release of ACh from postganglionic
neurons
 Slows heart rate, and increases digestive
activities
Summary of Autonomic Functions
Cholinergic Synaptic Transmission
a. Acetylcholine (ACh) is the neurotransmitter
secreted by all preganglionic neurons
(sympathetic and parasympathetic)
b. It is also the neurotransmitter released from most
parasympathetic postganglionic neurons.
c. Some sympathetic postganglionic neurons (those
that innervate sweat glands and skeletal muscle
blood vessels) release ACh.
d. These synapses are called cholinergic.
Adrenergic Synaptic Transmission
a. Norepinephrine is the neurotransmitter released
by most sympathetic postganglionic neurons.
b. These synapses are called adrenergic.
Response to Adrenergic Stimulation

Can be epinephrine in the blood or
norepinephrine from sympathetic nerves
 Can stimulate or inhibit, depending on receptors
a. Stimulation: heart, dilatory muscles of the iris,
smooth muscles of many blood vessels
(causes vessel constriction)
b. Inhibition: Bronchioles in lungs, other blood
vessels; inhibits contraction and causes dilation
of these structures
Neurotransmitters of the Autonomic
Nervous System
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Cranial
parasympathetic
nerves
Terminal
ganglion
ACh
Visceral
effectors
NE
Visceral
effectors
ACh
Paravertebral
ganglion
ACh
Adrenal
medulla
Sympathetic
(thoracolumbar)
nerves
ACh
E, NE (hormones)
Circulation
Visceral
effectors
NE
ACh
Sacral
parasympathetic
nerves
Collateral
ganglion
ACh
ACh
Visceral
effector
organs
Varicosities



Axons of postganglionic neurons have various
swellings called varicosities that release
neurotransmitter along the length of the axon.
They form “synapses en passant” - in passing.
Sympathetic and parasympathetic neurons
innervate the same tissues but release different
neurotransmitters
Sympathetic and Parasympathetic Release of
Different Neurotransmitters
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Sympathetic
neuron
Varicosity
Synapses
en passant
Smooth muscle cell
Parasympathetic
neuron
(a)
Axon of Sympathetic
Neuron
Synaptic vesicle
with norepinephrine (NE)
NE
Adrenergic
receptors
Antagonistic effects
Smooth
muscle cell
Cholinergic
receptors
ACh
Axon of Parasympathetic
Neuron
(b)
Synaptic vesicle
with acetylcholine (ACh)
3. α and β Adrenergic Receptors
a. Two types of α(alpha) - α1 and α2
b. Two types of β(beta) - β1 and β2
c. All act using G-proteins and second messenger
systems.
1) β receptors use cAMP.
2) α receptors use a Ca2+ second messenger
system.
d. Alpha receptors are more sensitive to
norepinephrine
e. Beta receptors are more sensitive to blood
epinephrine
f. α2 Receptors
1) Located on presynaptic axons
2) When stimulated, result in inhibition of
norepinephrine release in the synapse
a) May be a negative-feedback system
b) Some drugs to lower blood pressure act on
these α2 receptors to inhibit presynaptic
neurons in the brain, inhibiting the whole
sympathoadrenal system.
c) There are different subtypes that will give
different responses
*Adrenergic effects in different organs
Examples of Adrenergic and Cholinergic
Agonists and Antagonists
Response to Cholinergic Stimulation
1. ACh released from preganglionic neurons of both
the sympathetic and parasympathetic division is
stimulatory.
2. ACh from postganglionic neurons of the
parasympathetic division is usually stimulatory,
but some are inhibitory, depending on receptors.
3. In general, sympathetic and parasympathetic
effects are opposite
Cholinergic Receptors
Nicotinic: found in autonomic ganglia
1) Stimulated by Ach from preganglionic neurons
2) Serve as ligand-gated ion channels for Na+ & K+
3) Blocked by curare
Muscarinic: found in visceral organs and stimulated by
release of Ach from postganglionic neurons
1) Five types identified; can be stimulatory or
inhibitory (opening K+ or Ca2+ channels)
2) Use G-proteins and second messenger system
3) Blocked by atropine
Cholinergic Receptors & Responses to ACh
Comparison of Nicotinic & Muscarinic ACh
Receptors
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Nicotinic ACh
receptors
Muscarinic ACh
receptors
Postsynaptic membrane of
• All autonomic ganglia
• All neuromuscular junctions
• Some CNS pathways
• Produces parasympathetic nerve effects in
the heart, smooth muscles, and glands
• G-protein-coupled receptors (receptors
influence ion channels by means of G-proteins)
Na+
ACh
ACh
Ligand-gated channels
(ion channels are part
of receptor)
αβ
γ
αβ
γ
K+
Depolarization
K+
Hyperpolarization
(K+ channels
opened)
Excitation
Na+ or Ca2+
ACh
K+
Depolarization
(K+ channels
closed)
Inhibition
Excitation
Produces slower
heart rate
Causes smooth muscles of the
digestive tract to contract
Receptor Activity in Autonomic
Regulation
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Parasympathetic division
Sympathetic division
Preganglionic
neurons
ACh
Nicotinic
ACh receptors
Postganglionic
neurons
ACh
Norepinephrine
Stimulates
muscarinic ACh
receptors
Parasympathetic
nerve effects
Stimulates
α1-adrenergic
receptors
Stimulates
β1-adrenergic
receptors
Vasoconstriction in Increased
viscera and skin heart rate and
contractility
Stimulates
β2-adrenergic
receptors
Dilation of
bronchioles (of lung)
and blood vessels
Other Autonomic Neurotransmitters

Some postganglionic autonomic neurons do
not release ACh or norepinephrine.
a. Called “nonadrenergic, noncholinergic
fibers”
b. Proposed neurotransmitters include ATP,
vasoactive intestinal peptide (VIP), and nitric
oxide (NO).
Nonadrenergic, Noncholinergic Fibers



Important for erection of the penis.
Parasympathetic neurons innervate blood
vessels, causing relaxation and vasodilation using
NO.
NO can also produce smooth muscle relaxation in
the stomach, intestines, urinary bladder, and the
brain.
Organs with Dual Innervation

Most visceral organs are innervated by both
sympathetic and parasympathetic neurons.
 Most of the time these systems are antagonists:
a. Heart rate – sym increases, para decreases
b. Digestive functions – sym decreases, para
increases
c. Pupil diameter – sym dilates, para constricts
Complementary Effects


Occur when both divisions produce similar effects
on the same target
Example - Salivary gland secretion:
Parasympathetic division stimulates secretion of
watery saliva; sympathetic constricts blood
vessels so the secretion is thicker.
Cooperative Effects



Occur when both divisions produce different
effects that work together to promote a single
action.
Example - Erection and ejaculation:
Parasympathetic division causes vasodilation and
erection; sympathetic causes ejaculation
Example - Urination: Parasympathetic division
aids in urinary bladder contraction; sympathetic
helps with bladder muscle tone to control
urination.
Summary of Autonomic Functions
Organs Without Dual Innervation

The following organs are innervated by the
sympathetic division only:
a. Adrenal medulla
b. Arrector pili muscles in skin
c. Sweat glands in skin
d. Most blood vessels
 Regulated by increase and decrease in
sympathetic nerve activity
 Important for body temperature regulation through
blood vessels and sweat glands
Control of ANS by Higher Brain Centers

Many visceral functions are regulated by
autonomic reflexes.
a. Sensory input is sent to brain centers
(usually by the vagus nerve), which integrate
the information and modify the activity of
preganglionic neurons.
b. Medulla oblongata controls many
cardiovascular, pulmonary, urinary,
reproductive, and digestive functions.
Regulation of the Medulla

Higher brain regions regulate the medulla.
1) Hypothalamus: major regulatory center of the
ANS – body temperature, hunger, thirst,
pituitary gland
2) Limbic system: responsible for autonomic
responses during emotional states (blushing,
pallor, fainting, cold sweating, racing heart rate)
3) Cerebellum – motion sickness nausea,
sweating, cardiovascular changes
4) Frontal & temporal lobes – emotion and
personality
Aging
a. Associated with increased levels of sympathetic
activity
b. Increased sympathetic tone
c. Increased risk for hypertension and
cardiovascular diseases
Autonomic Reflexes