G6 Autonomic Nervous System

Question 1

What is the autonomic nervous system in the grand scheme of things?

Answer 1

It is the efferent division of the visceral nervous system. It is further divided into the sympathetic and parasympathetic nervous systems.

Question 2

Where do synapses happen in the ANS?

Answer 2

In a ganglion.

Question 3

How many neurons are involved in the pathways for the SNS and the PSNS?

Answer 3

Both systems use a two-neuron pathway to reach their targets.

Question 4

How do the SNS and PSNS work together in the innervation of organs?

Answer 4

Most organs are innervated by both systems, so they work against each other to produce the effect on the organ.

Question 5

In general terms, what are the characteristic effects of the SNS and the PSNS?

Answer 5

SNS: fight or flight response, has widespread effects
PSNS: rest and digest, localized efects

Question 6

Where are the pre and post ganglionic cell bodies of the SNS located?

Answer 6

PRE: IMLCC (intermediolateral cell column)
at spinal cord levels T1-L2

POST: in paravertebral ganglia and prevertebral ganglia

Question 7

Where are the pre and post ganglionic cell bodies located for the PSNS?

Answer 7

PRE: brainstem nuclei of certain cranial nerves and in S2-S4 spinal levels

POST: in intrinsic ganglia (in or near wall of target organ)

Question 8

How many neurons are in the pathway for the somatic nervous system?

Answer 8

One that goes from the CNS to the voluntary muscle. This is always the case.
Two-neuron pathways are unique to the ANS.

Question 9

How many neurons are in the afferent pathways for the somatic and visceral nervous systems?

Answer 9

Afferent is always a single neuron pathway to the CNS.

Question 10

What does “dual is the rule” mean and what exceptions are there?

Answer 10

It means that most organs receive dual antagonistic innervation from both the SNS and PSNS.
Exceptions are the visceral components of the body wall (sweat and sebaceous glands, arrector pili, vascular smooth muscle) and the adrenal gland. All these receive only SNS innervation.

Question 11

What does the cranial nerve X or the vagus nerve innervate?

Answer 11

Visceral organs of the thoracic and abdominal cavities to the proximal 2/3 of transverse colon.

Question 12

Where are the pregang. cell bodies for PSNS sacral portion?

Answer 12

In the intermediate zone of the spinal cord gray matter, and they exit the spinal cord at levels S2-S4. These are pelvic splanchnic nerves.

Question 13

What do the sacral PSNS neurons innervate?

Answer 13

The distal 1/3 of the colon and the pelvic viscera (such as the bladder)

Question 14

Where are the paravertebral and prevertebral ganglia?

Answer 14

paravertabral is lateral

prevertebral is anterior, on both lateral sides of the descending aorta

Question 15

Where does the spinal cord end?

Answer 15

At the L1-L2 intervertebral disc level.

Question 16

Explain spinal cord level vs vertebral or spinal nerve level and their relationships to ant/pos roots, pos root ganglion, spinal nerve, and gray/white rami.

Answer 16

Ant/pos roots originate at respective spinal cord level

Pos root ganglion, spinal nerve, and gray/white rami are located at their appropriate vertebral level (spinal nerve level)

Question 17

What go through the white and gray rami?

Answer 17

Both connect the paravertebral ganglia with the ANTERIOR rami of spinal nerves.

White rami: pregang. sympathetic axons enter the sympathetic chain
Gray rami: postgang. sympathetic axons exit the chain and rejoin the anterior rami of spinal nerves

Question 18

Where are the white and gray rami found?

Answer 18

Because sympathetic pregang. cell bodies are only found at T1-L2, these are the only levels where white rami are found.

Because postgan. axons can exit the chain at any level, gray rami are found at all the spinal nerve (vertebral) levels.

Question 19

What are the three ways for sympathetic neurons to reach their targets?

Answer 19

1. Body wall and limbs: synapse in paravertebral ganglion, then rejoin spinal nerve and go to target
2. Thoracic viscera: synapse in paravertebral ganglion, then form cardiopulmonary splanchnic nerve
3. Abdomino/pelvic viscera: through paravertebral ganglion without synapsing, then down the abdominopelvic splanchnic nerve then synapse in prevertebral ganglion, then follow arteries to target

Question 20

What are the two types of visceral sensation?

Answer 20

Non-Pain: mechanoreceptors, baroreceptors, chemoreceptors, thermoreceptors

Pain: nociceptors (distension, ischemia, chemical irritation)

Question 21

How do the two types of visceral sensation get back to the CNS?

Answer 21

Non-pain: through the PSNS responsible for innervating the structure back through the vagus nerve or splanchnic nerves to the inferior ganglion of vagus nerve or the PRG of S2-S4, pseudounipolar neuron

Pain: through the SNS responsible for innervating that structure, through the PRG of T1-L2, pseudounipolar neuron

Question 22

What divisions of the nervous system have pseudounipolar nerves?

Answer 22

The sensory nerves (afferent) from both the somatic and the visceral nervous systems. The cell bodies are located in the posterior root ganglion.

Question 23

The neurons of which nervous system division pass through the paravertebral ganglia?

Answer 23

The visceral sympathetic and pain nerves do, but only the sympathetic nerves synapse there.