Visceral Autonomic Nervous System Flashcards
What tissues are innervated by the ANS?
smooth muscle
cardiac muscle
glands
In general, where are the 2 neurons in the ANS located?
the first is in the brain stem or spinal cord (in the CNS)
the second is in a peripheral ganglion (motor)
What are the two branches of the ANS?
sympathetic and parasympathetic
Where are the sympathetic preganglionic neuron cell bodies located?
in the lateral horns of the spinal cord segments T1-L2
Where are parasympathetic preganglionic neuron cell bodies located?
in the cranial nerve nuclei of the CN 3, 7, 9, and 10 and the spinal cord segments S2-S4
Where do the presynaptic neurons synapse in the sympathetic systems?
3 choices:
they synapse onto the postganglionic neuron in the paravertebral ganglia or sympathetic chain along the sides fo the spinal cord
they pass through the paravertebral ganglia into the splanchnic nerves and synapse onto the postganglion neuron in the prevertebral ganglia
they pass through the ganglia iwthout synapsing and synapse on the secretory cells of the adrenal gland
How doe the sympathetic preganglionic nerve fibers get to the paravertebral ganglia?
THey leave the spinal cord through the ventral roots and join the spinal nerve
they enter the ventral rami
soon after entering the rami, they enter a white ramus communicans which is attached to the paravertebral ganglia
Once the preganglionic neuron is in the paravertebral ganglia, what are its 4 options?
- it can synapse right at that same level
- It can ascend to terminate at a higher paravertebral level
- It can descend to a lower paravertebral level
- I can traverse the sympathetic trunk without terminating and form splanchnic or visceral nerves
Where must sympathetic innervation of the head come from?
remember that all sympathetic nerves originate in the thoracolumbar spinal cord - NOT the cervical. So the head comes from around T1-T2.
Why are white rami communicans white?
the axons inside are myelinated
Besizdes the preganglionic sympathetic axons, what could be present in the white communicating rami?
visceral sensory fibers
How many pairs of white rami are there in the spinal cord?
14 pairs - 28 total
Paravertebral ganglia are usually arranged segmentally with one per spinal nerve EXCEPT in what region?
cervical - there are only 3
these have communications with the 8 cervical spinal nerve
How do the paravertebral ganglia communicate the postganglionic sympathetic fibers back to the 31 pairs of spinal nerves?
through gray rami communicans
thus, there are 31 pairs of gray rami
How do sympathetic postganglion fibers reach the head?
they go thorugh the cephalic arterial branches
(also called the periarterial sympathetic plexus)
they leave the superior cervical ganglia and jump onto the carotic arteris (or any other vessel) and follow them to their destinations
Why is the superior cervical ganglion the largest of the cervical ganglia?
because thats where the postganglionic fibers for the head come out
How to postganglionic axons reach the heart, lungs, and esophagus?
They leave the paravertebral ganglia via cardiopulmonary nerves that supply the cardiac, pulmnary and aortic plexuses
Where are the cell bodies of the cardiopulmonary nerves?
they are in the middle and inferior cervical paravertebral ganglia or in the upper 5 thoracic paravertebral ganglia
What are the 3 main prevertebral ganglia?
celiac ganglion
superior mesenteric ganglion
inferior mesenteric ganglion
How do preganglionic fibers get to the prevertebral ganglia from the sympathetic chain?
they leave the sympathetic chain through splanchnic nerves
What are the equivalents of postganglioni neurons in the suprarenal medulla? WHat do they do?
the secretory cells fo the suprarenal medulla
they release primarily epinephrine into the vascular system
What neurotransmitter is released from preganglionic sympathetic neurons? What receptor do they act on?
they release acetylcholine which acts on nicotninic receptors located in the membrane of postganglionic neurons
What NT do the postganglionic neurons release? Onto what receptors?
norepinephrine on alpha or berta receptors on the target organ
What alpha/beta recetors are excitatory? Which are inhibitory?
alpha and beta 1 are excitatory
alpha 2 and beta 2 are inhibitory
Where are preganglionic cell bodies located in the parasympathetic system?
brain stem (for CN 3, 7, 9, 10) and sacral spinal cord (S2-4)
Where are the parasympathetic postganglionic cell bodies?
the ones in the head regions are in distinct cranial ganglia
those from the vagus nerve and sacral regions are in or near the organ of innervation in terminal ganglia
WHat NT is released by preganglionic parasympathetic neurons? on what receptor?
WHat NT is released by postganglionic parasympathetic neurons? On what receptor?
Preganglionic: ACh on nicotinic receptors
Postganglionic: ACh on muscarinic receptors
Which ANS system has short presynaptic neurons and long postsynatic neurons?
Which has the reverse?
sympathetic
the reverse is parasympathetic
WHy type of fibers are in the myenteric nerve plexus?
postganglionic parasympathetic neurons
this is an example of a terminal ganglion in the organ of innervtion
