Transcript Slide 1

The Autonomic Nervous System
The Autonomic
Nervous System
Visceral sensory
&
Visceral motor
Autonomic nervous system
 The autonomic nervous system is the
subdivision of the peripheral nervous
system that regulates body activities that
are generally not under conscious control
 Visceral motor innervates non-skeletal
(non-somatic) muscles
 Visceral sensory
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To repeat…
 ANS is the subdivision of the peripheral nervous
system that regulates body activities that are
generally not under conscious control
 Visceral motor innervates non-skeletal (nonsomatic) muscles
 Composed of a special group of neurons serving:
 Cardiac muscle (the heart)
 Smooth muscle (walls of viscera and blood vessels)
 Glands
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Basic anatomical difference between the motor
pathways of the voluntary somatic nervous
system (to skeletal muscles) and those of the
autonomic nervous system
 Somatic division:
 Cell bodies of motor neurons reside in CNS (brain or
spinal cord)
 Their axons (sheathed in spinal nerves) extend all the
way to their skeletal muscles
 Autonomic system: chains of two motor neurons
 1st = preganglionic neuron (cell body in brain or cord)
 2nd = postgangionic neuron (cell body in ganglion
outside CNS)
 Slower because lightly or unmyelinated
(see next diagram)
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 Axon of 1st (preganglionic) neuron leaves
CNS to synapse with the 2nd (ganglionic)
neuron
 Axon of 2nd (postganglionic) neuron
extends to the organ it serves
Diagram contrasts somatic (lower) and autonomic:
autonomic
this dorsal
root ganglion
is sensory
somatic
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Note: the autonomic ganglion is motor
Divisions of the autonomic nervous system
(visceral motor part of it)
 Parasympathetic division
 Sympathetic division
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Divisions of the autonomic nervous system
 Parasympathetic division
 Sympathetic division
Serve most of the same organs but
cause opposing or antagonistic effects
Parasysmpathetic: routine maintenance
“rest &digest”
Sympathetic: mobilization & increased metabolism
“fight, flight or fright” or “fight, flight or freeze” 9
Where they come from
Parasympathetic:
craniosacral
Sympathetic:
thoracolumbar
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Sympathetic nervous system
“fight, flight or fright”
 Also called thoracolumbar system: all its neurons
are in lateral horn of gray matter from T1-L2
 Lead to every part of the body (unlike parasymp.)
 Easy to remember that when nervous, you sweat; when
afraid, hair stands on end; when excited blood pressure
rises (vasoconstriction): these sympathetic only
 Also causes: dry mouth, pupils to dilate, increased heart
& respiratory rates to increase O2 to skeletal muscles,
heart and brain
 Norepinephrine (noradrenaline) is
neurotransmitter released by most postganglionic
fibers (acetylcholine in preganglionic): “adrenergic”
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Sympathetic
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The preganglionic neuron projects from the spinal cord out the ventral
root (just like motor neurons do).
The preganglionic neuron sends its axon down white ramus
communicans to reach a ganglion within the sympathetic trunk
These fibers now have one of the following TWO options:
1- synapse in a paravertebral ganglion
2- synapse in a collateral ganglion
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paravertebral ganglion
When the preganglionic axon reaches the paravertebral ganglion, it synapses on a
postganglionic neuron. The preganglionic axon may also send off branches to
synapse on other postganglionic neurons in the same or nearby paravertebral
ganglia
The postganglionic neuron sends its axon out the gray ramus communicans
The postganglionic axon runs from the gray ramus communicans out through the
spinal nerve toward the skin ( mainly targets like the arrector pili muscles and blood
vessels and glands)
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Collateral ganglion
bypasses this paravertebral ganglion to continue to project away from the
spinal cord in a separate nerve (splanchnic nerves
The preganglionic axon reaches the collateral ganglion via the splanchnic nerve
and synapses on a postganglionic neuron within it. The postganglionic neuron
then projects its axon to synapse on its target
collateral ganglia tend to influence the deeper visceral organs (heart, kidneys,
and digestive system)
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The ratio of preganglionic to postganglionic
sympathetic is about 1:10 Permitting a wide
control of involuntary structures
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Sympathetic trunks
 two ganglionated nerve trunks that extends the whole length of vertebral column
Each trunk has:
 3 ganglia In the neck
11 or 12 ganglia in the thorax
 4 or 5 in the lumber region
 4 or 5 in the pelvis
Below, the two trunks end by joining together to form a single ganglion
(ganglion impar)
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Parasympathetic nervous system
“rest & digest”
 Also called the craniosacral system
because all its preganglionic neurons are
in the brain stem or sacral levels of the
spinal cord
 Cranial nerves III,VII, IX and X
 In lateral horn of gray matter from S2-S4
 Only innervate internal organs
 Acetylcholine is neurotransmitter at end
organ as well as at preganglionic synapse:
“cholinergic”
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Parasympathetic continued
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pupils constrict
Stimulates digestive glands
Increases motility of smooth muscle of digestive tract
Decreases heart rate
Causes bronchial constriction
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Parasympathetic
(only look at this
if it helps you)
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The myleinated efferent fibers of the craniosacral outflow are
preganglionic and synapse in peropheral ganglia located close
To the viscera they innervate
The ratio of preganglionic to postganglionic
sympathetic is about 1:3 or less, which is much
More restricted than in sympathetic part of the system
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