Download The Autonomic Nervous System

Biology 211
Anatomy & Physiology I
Autonomic
Nervous
System
We have discussed how nerves carry
motor and sensory information to and
from different parts of the body
but
Certain tissues require a different type
of innervation.
These are smooth muscle tissue
cardiac muscle tissue
glands
found in many different organs of the body
Autonomic Nervous System
The efferent (motor) component of the peripheral nervous
system includes two types of neurons:
Somatic Neurons regulate voluntary movement
(contraction of skeletal myocytes)
Autonomic Neurons regulate involuntary functions
(rate & force of of cardiac myocyte contraction)
(contraction of smooth myocytes)
(secretion of glands)
Both types of neurons run through the same nerves.
For example, the vagus nerve (cranial nerve #10) contains
somatic motor neurons which control contraction of skeletal
myocytes in muscles of the pharynx during swallowing
AND
autonomic motor neurons controlling contraction of cardiac
myocytes and of smooth myocytes in the digestive system
Somatic and autonomic neurons follow different pathways
Somatic
Autonomic
Voluntary
Effectors: Skeletal M.
Involuntary
Effectors: Cardiac M.
Smooth M
Glands
Neurons extend from
CNS to effectors
without synapsing.
Two neurons to get from
CNS to effectors; therefore
one synapse.
"Two neuron chain"
Autonomic Nervous System has two divisions based
on two criteria:
a) Where the cell body of the first neuron is located
(In the brain or in a specific region of spinal cord)
b) Where the axon of the first neuron synapses with
the dendrites of the second neuron
(far away from the effector cells, or near effector cells)
Since there are always two neurons between the central
nervous system and the effector cells in an autonomic
pathway, they must synapse somewhere.
They do so in a ganglion located somewhere in the body
(more about this in a moment)
First cell = Preganglionic neuron
Second cell = Postganglionic neuron
Postganglionic
Neuron
Preganglionic
Neuron
Sympathetic Division of Autonomic Nervous System
Preganglionic neuron starts in thoracic or lumbar
levels of spinal cord.
Preganglionic neuron synapses with postganglionic
neuron in a ganglion relatively far from effector cells
Parasympathetic Division of Autonomic Nervous System
Preganglionic neuron starts in brain or sacral level
of spinal cord.
Preganglionic neuron synapses with postganglionic
neuron in a ganglion very near the effector cells
As we will see in a few minutes,
these two divisions of the autonomic
nervous system innervate the same
effector cells but have different
effects on those cells
Let’s Start Out With The Sympathetic Division
of the autonomic nervous system
Preganglionic neurons start in the
thoracic or lumbar levels of the
spinal cord
and
They synapse with postganglionic
neurons in ganglia which are
located relatively far from the
effector cells (smooth myocytes,
cardiac myocytes,
gland cells)
Sympathetic Division of the autonomic nervous system
That synapse between
preganglionic neurons and
postganglionic neurons can
occur in either of two sets of
ganglia:
Paravertebral Ganglia
Prevertebral Ganglia
Note: Since there are only two neurons which reach from
the central nervous system to the effector cells,
a sympathetic synapse can occur in either set of
ganglia, but not both
Sympathetic Division of the autonomic nervous system
1) Some preganglionic sympathetic neurons synapse with
their postganglionic neurons in paravertebral ganglia
which form a “chain” next to the vertebrae
(Sympathetic Division)
Note that the chain of
paravertebral ganglia
extends up into the neck
to supply sympathetic
innervation to structures
in the head, neck, and
upper thorax
Three things can happen in a paravertebral ganglia
of the sympathetic division:
A. The preganglionic
and postganglionic
neurons synapse in the
ganglion at the same
level.
The axon of the
postganglionic neuron
goes back into the spinal
nerve at the same level
to reach its effector cells.
Three things can happen in a paravertebral ganglia
of the sympathetic division:
B. The preganglionic
neuron enters the
ganglion but goes up or
down one or more levels
before it synapses with the
postganglionic neuron.
The axon of the
postganglionic neuron
then goes back into the
spinal nerve at this new
level to reach its effector
cells.
Three things can happen in a paravertebral ganglia
of the sympathetic division:
C. The preganglionic
neuron just passes
through the ganglion and
continues to a prevertebral
ganglion, where it
synapses with the
postganglionic neuron.
The axon of the
postganglionic neuron
then goes directly to its
effector cells in the
abdomen.
(Sympathetic Division of the autonomic nervous system)
2) Preganglionic sympathetic neurons in pathways to
abdominal organs pass through the paravertebral
ganglia (see previous slide) to synapse with their
postganglionic neurons in prevertebral ganglia which
are located near major arteries of the abdomen.
There are three of these prevertebral ganglia:
Celiac ganglion
Superior mesenteric ganglion
Inferior mesenteric ganglion
The second part of the autonomic nervous system is its
Parasympathetic Division
Preganglionic parasympathetic
neurons start in the brainstem or
in sacral levels of the spinal cord
and
They synapse with postganglionic
parasympathetic neurons in
ganglia which are located
relatively near the effector cells:
(smooth myocytes,
cardiac myocytes,
gland cells)
The other part of the autonomic nervous system is its
Parasympathetic Division
1. In the head, there are four
larger parasympathetic ganglia
located near the effector cells
Ciliary ganglion
(posterior to eye in orbit)
Pterygopalatine ganglion
(posterior to maxilla)
Submandibular ganglion
(near angle of mandible)
Otic ganglion
(inferior to foramen ovale)
The other part of the autonomic nervous system is its
Parasympathetic Division
2. Below the head: small
parasympathetic ganglia are
located within the
walls of target organs
such as intestines, heart,
uterus, etc.
Parasympathetic Autonomic Ganglia
Usually very small,
often only a few dozen
neuron cell bodies
Most organs have both sympathetic and
parasympathetic innervation, each of which acts in
opposition to the other to balance the functions of the
effector cells.
Most organs have both sympathetic and
parasympathetic innervation, each of which acts in
opposition to the other to balance the functions of the
effector cells.
Sympathetic:
Fear
Fight
Flight
F
Parasympathetic:
"Rest, Digest, and Foreplay"
Most organs have both sympathetic and
parasympathetic innervation, each of which acts in
opposition to the other.
For example:
Heart:
Sympathetic increases heart rate & force of contraction
Parasympathetic decreases heart rate & force of contraction
Most organs have both sympathetic and
parasympathetic innervation, each of which acts in
opposition to the other.
For example:
(Heart: Sympathetic increases rate & force
Parasympathetic decreases rate & force )
Lungs:
Sympathetic dilates air passages
Parasynpathetic constricts air passages
Most organs have both sympathetic and
parasympathetic innervation, each of which acts in
opposition to the other.
For example:
(Heart: Sympathetic increases rate & force
Parasympathetic decreases rate & force )
(Lungs: Sympathetic dilates air passages
Parasynpathetic constricts air passages)
Digestive System:
Sympathetic decreases activity; constricts anal sphincter
Parasympathetic increases activity; relaxes anal sphincter
Most organs have both sympathetic and
parasympathetic innervation, each of which acts in
opposition to the other.
For example:
(Heart: Sympathetic increases rate & force
Parasympathetic decreases rate & force )
(Lungs: Sympathetic dilates air passages
Parasynpathetic constricts air passages)
(Digestive System: Sympathetic decreases activity
Parasympathetic increases activity)
Urinary System:
Sympathetic inhibits urination
Parasympathetic promotes urination