Autonomic Nervous System
Neural Control of Involuntary
Effectors
ANS:
 Innervates organs not usually under voluntary
control.
 Effectors include cardiac and smooth muscles
and glands.
 Effectors are part of visceral organs and blood
vessels.
Effectors
► The effectors of the
SNS are skeletal
Muscles
► The effectors of the
ANS are cardiac
muscle, smooth
muscle, and glands
Autonomic Neurons
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2 neurons in the effector pathway.
1st neuron has its cell body in gray
matter of brain or spinal cord.
– Preganglionic neuron.

Synapses with 2nd neuron within an
autonomic ganglion which extends to
synapse with effector organ.
– Postganglionic neuron.
Autonomic Neurons

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Autonomic ganglia are located in the
head, neck, and abdomen.
Presynaptic neuron myelinated and
postsynaptic neuron unmyelinated.
Morphological characteristics of ANS
Autonomic nervous system
Parasympathicus
Sympathicus
• Ganglia close to
innervated organs
• Ganglia close to
spinal cord
• Myelinated axons
• Preganglionic
axons myelinated
• Postganglionic nonmyelinated
• Заб:
Соматичната
нервна система
няма ганглии
Sympathetic Division
►Also known as
The Thoracolumbar Division
􀂃􀂃 T1 through L2
►More complex
►Consists of a
Chain of ganglia
Sympathetic Division

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Myelinated preganglionic exit
spinal cord in ventral roots at T1
to L2 levels.
Travel to ganglia at different
levels to synapse with
postganglionic neurons.
Divergence:
– Preganglionic fibers branch to
synapse with numerous
postganglionic neurons.
Convergence:
– Postganglionic neuron receives
synaptic input from large # of
preganglionic fibers.
Sympathetic Chain Ganglion
► Located on either side of spinal
cord
► Extends from base of skull to
coccyx
► 23 arranged segmentally in
each trunk
􀂃􀂃 3 cervical, 11 thoracic,
4 lumbar, 4 sacral and
1 coccygeal.
► Rami communicans attach
chain to spinal
Sympathetic Division
► “Fight-or-flight” system
► Release of norepinephrine from postganglionic
fibers and epinephrine from adrenal medulla.
► Excitatory effect in all areas except digestive
organs
► Promotes adjustments during exercise
􀂃􀂃  Blood flow to organs is reduced, flow to
muscles is increased
► Prepares the body for emergency situations
– Heart rate increases.
– Bronchioles dilate.
– Breathing is rapid and deep
– [glucose] increases.
Parasympathetic Division
► Also known as Craniosacral Division
► Concerned with keeping body energy
use low (“housekeeping”)
 Its activity is illustrated in a person
who is in a relaxed state
 Blood pressure, heart rate, and
respiratory
rates are low
 Gastrointestinal tract activity is high
► Inhibitory effect
Parasympathetic Division
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Preganglionic fibers originate
in midbrain, medulla, and
pons; and in the 2-4 sacral
levels of the spinal cord.
Preganglionic fibers synapse in
ganglia located next to or
within organs innervated.
Do not travel within spinal
nerves.
– Do not innervate blood vessels,
sweat glands,and arrector pili
muscles.
Parasympathetic Division
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4 of 12 pairs of cranial nerves contain
preganglionic parasympathetic fibers.
Preganglionic fibers are long, postganglionic
fibers are short.
Vagus:
– Innervate heart, lungs esophagus, stomach,
pancreas, liver, small intestine and upper half of
the large intestine.
Parasympathetic Division
Cranial Outflow
►Oculomotor (III):
􀂃􀂃 Smooth muscles of eye
►Facial (VII):
􀂃􀂃 Facial muscles
Facial glands
►Lacrimal
►Salivary
Cranial Outflow
► Glossopharyngeal (IX)
􀂃􀂃 Salivary glands
►Vagus (X)
􀂃􀂃 Postganglionic fibers are
in the target organ.
􀂃􀂃 Parasympathetic fibers
to heart, lungs, bronchi,
stomach, esophagus,liver,
small intestine, pancreas,
kidneys, proximal part of the
large intestine.
Parasympathetic Division
Sacral Outflow
►Arises from gray matter in
spinal cord segments S2-S4.
►Innervate distal part of large
intestine, bladder, ureters, and
the reproductive organs
Parasympathetic Effects
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Stimulation of separate parasympathetic
nerves.
Release ACh.
Relaxing effects:
– Decrease heart rate (HR).
– Dilate blood vessels.
– Increase GI activity.
Interneuron contacts in sympathetic and
parasympathetic ganglion
Adrenergic and Cholinergic Synaptic
Transmission
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ACh is NT for all preganglionic fibers of both
sympathetic and parasympathetic nervous
systems.
ACh is NT released by most postganglionic
parasympathetic fibers.
Transmission at these synapses is termed
cholinergic.
Differences between sympathetic
and parasympathetic divisions
Autonomic nervous system controls physiological arousal
Sympathetic
division (arousing)
Pupils dilate
Parasympathetic
division (calming)
EYES
Pupils contract
SALIVATION
Increases
Perspires
SKIN
Dries
Increases
RESPIRATION
Decreases
Accelerates
HEART
Slows
Inhibits
DIGESTION
Activates
Secrete stress
hormones
ADRENAL
GLANDS
Decrease secretion
of stress hormones
Decreases
Organs with Dual Innervation
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Most visceral organs receive dual
innervation (innervated by both
sympathetic and parasympathetic fibers).
Antagonistic effects:
– Actions counteract each other.
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Heart rate.
Complementary:
– Produce similar effects.
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Salivary gland secretion.
Cooperative:
– Cooperate to produce a desired effect.
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Micturition.
Enteral nervous system

Described 70 years ago, its morphological and
functional study began in 1990.

The neurons (>100 mill) outnumber those in the
spinal cord.

Forms extensive network of interconnected
ganglia.
Structure

Plexus myentericus
– Between longitudinal and circular muscle layer
in the digestive canal
– From the pharynx to the anus

Plexus submucosus
– In the submucosal layer of intestines, from the
stomach to the anus

Ganglia in each plexus are extensively
interconnected neurons
Enteral division
Function
Controls the activity of gastrointestinal tract in three
ways:
1) Controls peristalsis
2) Modulated blood flow in the intestines
3) Regulates secretion from the intestinal glands
Each activity can be influenced by sympathetic
parasympathetic impulses, but the enteral system
receives own sensory information from the
intestines and can act semiautomatically.
Regulation. Autonomic reflexes
Control by Higher Brain Centers
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Sensory input transmitted to brain centers that
integrate information.
Can modify activity of preganglionic autonomic
neurons.
Medulla:
– Most directly controls activity of autonomic system.
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Hypothalamus:
– Regulates medulla.
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Cerebral cortex and limbic system:
– Responsible for responses to emotion.
Higher centers of autonomic regulation
Responses to Adrenergic Stimulation
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Has both excitatory and inhibitory
effects.
Responses due to different membrane
receptor proteins.
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a1 : constricts vascular smooth muscles
a2 : contraction of smooth muscle
b1 : increases HR and force of contraction
b2 : relaxes bronchial smooth muscles
Responses to Cholinergic Stimulation
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Muscarinic receptors:
– Ach binds to receptor.
– Requires the mediation of G-proteins.
– Beta-gamma complex binds to chemical K+
channel, opening the channel.
Functions to:
– Decrease HR.
– Decrease force of contraction of the heart.
– Produce bronchiole constriction.
– Increase GI secretions.
Other Autonomic NTs
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Certain postganglionic autonomic axons
produce their effects through other NTs.
– ATP
– VIP
– NO