1. Biology 322 Human Anatomy I
Autonomic Nervous System

2. Autonomic Nervous System

3. 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 cardiac myocyte contraction)
(contraction of smooth myocytes)
(secretion of glands)
Both types of efferent neurons run through the same cranial or spinal nerves

4. Comparison: Somatic vs Autonomic efferent neurons
Voluntary Involuntary
Effectors: Skeletal M 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"

5. Autonomic Nervous System has two divisions based on two criteria:
a) Where the cell body of the first neuron is located
(Brain, or specific region of spinal cord)
b) Where the axon of the first neuron synapses with
the dendrites of the second neuron
(Far away from effector cells; or near effector cells)

6. They do so in a ganglion located somewhere in the body
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

7. Sympathetic Division of Autonomic Nervous System
Preganglionic neuron starts in thoracic
or lumbar levels of spinal cord.
Preganglionic neuron synapses with
postganglionic neuron relatively far
from the 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 very near the
effector cells

8. 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)

9. 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

10. Sympathetic Division of the autonomic nervous system
Some preganglionic sympathetic neurons synapse with their postganglionic neurons in paravertebral ganglia which form a “chain” next to the vertebrae

11. (Sympathetic Division)
Note that this chain of paravertebral ganglia extends up into the neck to supply sympathetic innervation to structures in the head, neck, and upper thorax

12. 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
and
The axon of the postganglionic neuron goes back into the spinal nerve at the same level to reach its effector cells.

13. 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
and
The axon of the postganglionic neuron then goes back into the spinal nerve at this new level to reach its effector cells.

14. 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.

15. (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

16. The second half 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)

17. The second half of the autonomic nervous system is its Parasympathetic Division
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)

18. 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.

19. Parasympathetic Autonomic Ganglia
Usually very small, often only a few dozen neuron cell bodies

20. 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.

21. 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
Sexual intercourse, orgasm, ejaculation
Parasympathetic:
"Rest, Digest, and Sexual Foreplay"

22. For example:
Heart:
Sympathetic increases heart rate & force of contraction
Parasympathetic decreases heart rate & force of contraction

23. For example:
(Heart: Sympathetic increases rate & force
Parasympathetic decreases rate & force )
Lungs:
Sympathetic dilates air passages
Parasynpathetic constricts air passages

24. 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

25. 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