Autonomic Nervous System

Question 1

What nucleus receives inputs from visceral afferents?

Answer 1

Nucleus of the solitary tract

Question 2

What CNs control parasympathetic output?

Answer 2

CN III, VII, IX, and X

Question 3

What results to autonomic regulation if there is a cervical spinal cord transection?

Answer 3

1. Reticulospinal inputs to sympathetic output neurons is lost
2. Reticulospinal inputs to sacral parasympathetic output neurons is lost.
3. Results in loss of blood pressure control by sympathetic neurons and bladder control.

Question 4

What largely regulates activity of sympathetic and parasympathetic output neurons?

Answer 4

Reticular formation, which integrates inputs from NTS, hypothalamus, and other areas.

Question 5

What is the difference between the white and gray rami?

Answer 5

Preganglionic sympathetic fibers leave the spinal nerve (after exiting the ventral root) and pass through the white ramus into sympathetic ganglia chain.
Postganglionic sympathetic fibers arising from paravertebral ganglia pass back from sympathetic chain into spinal nerves through gray rami.

Question 6

What are the two locations of the cell bodies of sympathetic postganglionic neurons?

Answer 6

Paravertebral ganglia and prevertebral ganglia (paravertebral are ganglia of sympathetic chain, prevertebral ganglia are ganglia of the periphery)

Question 7

What is the importance of postganglionic sympathetic fibers in the skeletal nerves?

Answer 7

These fibers pass back from sympathetic chain into spinal nerves through gray rami, and travel to the body in skeletal nerves. These nerves innervate smooth muscle targets.

Question 8

What are the 4 fates of the preganglionic sympathetic fibers after entering the ganglia?

Answer 8

1. Synapse with postganglionic neurons in the ganglion it enters
2. Pass up or down the chain and synapse with other ganglia
3. Pass through the sympathetic nerves to terminate in the prevertebral ganglia
4. Pass without synapsing all the way from the cell column of the spinal cord through the sympathetic nerves to the adrenal medulla.

Question 9

What is the location of the parasympathetic preganglionic neurons?

Answer 9

Brainstem and sacral spinal cord. Vagus nerve contains 75% of all parasympathetic preganglionic axons

Question 10

What are the targets of parasympathetic outflow of CN III?

Answer 10

Sphincter pupillae (pupillary constriction) and muscles of ciliary body (controlling the shape of the lens).

Question 11

What are the targets of parasympathetic outflow of CN VII?

Answer 11

Salivary glands (except parotid) and lacrimal and nasal glands

Question 12

What are the targets of parasympathetic outflow of CN IX?

Answer 12

Parotid gland

Question 13

What are the targets of parasympathetic outflow of CN X?

Answer 13

Nearly all thoracic and abdominal viscera

Question 14

What are the targets of parasympathetic outflow of the sacral spinal cord?

Answer 14

Distal colon, rectum, bladder, lower portion of ureters, external genitalia

Question 15

What is the total synthetic pathway to make epinephrine? What degrades epinephrine?

Answer 15

Tyrosine -> L-dopa (via Tyrosine hydroxylase) -> dopamine (via DOPA decarboxylase) -> norepinephrine (via dopamine-beta hydroxylase) -> epinephrine (via PNMT). COMT degrades epinephrine (catechol-O-methyltransferase)

Question 16

What type of ACh receptor is on autonomic ganglia?

Answer 16

A distinct subtype of nicotinic ACh

Question 17

What is the sensitivity of alpha and beta receptors for epinephrine and norepinephrine?

Answer 17

Alpha1/2: NE > Epi
Beta 1: NE = Epi
Beta 2: Epi > NE

Question 18

What sympathetic receptors are present over the heart’s conduction system?

Answer 18

Primarily beta-1 receptors

Question 19

What does the eye’s radial muscle do and what is its sympathetic receptor?

Answer 19

When sympathetically activated on its alpha1 receptor, the muscle contracts which causes widening of the pupil

Question 20

What eye muscle controlling pupil dilation is innervated by sympathetic inputs? parasympathetic inputs?

Answer 20

Sympathetic inputs are onto the radial muscle which widens pupil when the muscle contracts.
Parasympathetic inputs are onto the sphincter muscle which when it contracts causes closing of the pupil

Question 21

What is the bidirectional control of the ciliary muscle of the eye?

Answer 21

Ciliary muscle controls the lens.
When acted on by sympth inputs to beta2 receptors, results in relaxation of muscle to flatten lens for far vision
When acted on by parasympth inputs, the muscle contracts to make lens more convex for near vision.

Question 22

What sympathetic receptor is on the bronchial muscle?

Answer 22

Beta2, causing relaxation of muscle. Parasympathetic input causes contraction of the muscle

Question 23

What autonomic control of skeletal muscle is there?

Answer 23

Only sympathetic control via beta2 receptors to increase contractility

Question 24

What are the predominant inputs to sympathetic preganglionic neurons?

Answer 24

Comes from the brainstem, mainly areas of the reticular formation, and the hypothalamus.

Question 25

Just rattle off everything you know about Viagra.

Answer 25

Viagra acts as an inhibitor of phosphodiesterase type 5 (PDE5). Blocking PDE5 increases the duration which NO is active in smooth muscle cells. NO acts on the smooth muscle of blood vessel walls to cause vasodilation. Parasympathetic innervation of the blood vessels in the genitalia results in release of NO, NO produces vasodilation by activating guanylate cyclase, increasing cGMP levels. cGMP pumps calcium out of smooth muscle, inhibiting interactions of actin and myosin and causing muscle relaxation.