Autonomic Nervous System

Question 1

How does two-neuron relay work in sympathetic and parasympathetic nervous systems?

Answer 1

efferent ANS fibers leaving the CNS are preganglionic, and release ACh in peripheral autonomic ganglia to excite postgaglionic neurons that innervate peripheral targets

Question 2

What is the difference between parasympathetic and sympathetic motor nerve fiber neurotransmitter release?

Answer 2

sympathetic nerve fibers are adrenergic: release norepinephrine by exocytosis from their varicosities

parasympathetic nerve fibers are cholinergic: release acetylcholine by exocytosis of vesicles from their varicosities

Question 3

What are varicosities?

Answer 3

swellings like bead on a string no postganglionic neurons that allow them to release neurotransmitters in a “sprinkling” fashion along their axons

Question 4

Where are nicotinic ACh receptors found in the ANS?

Answer 4

cholinergic synapses on skeletal muscle end-plates (neuromuscular junction)

synapses on postganglionic neurons in autonomic ganglia

adrenal chromaffin cells

Question 5

What are the characteristics of Nicotinic ACh receptors?

Answer 5

fast ligand-gated ion channels

depolarizing - initiate action potentials

nonselective ion channels

relay electrical excitation from one cell to the next

Question 6

What is the role of nicotinic receptors in ganglion?

Answer 6

they relay preganglionic action potentials as postganglionic action potentials

Question 7

What receptors are the principal receptors in the target organs of the sympathetic and parasympathetic nerves?

Answer 7

GCPRs

Question 8

Which specific GCPRs are key for the autonomic nervous system?

Answer 8

Muscarinic ACh receptors

adrenergic receptors

additional receptors that respond to cotransmitters like NO, ATP, and peptides

Question 9

What is the function of Muscarinic ACh receptors of target organs of the ANS?

Answer 9

mediate parasympathetic effects

Question 10

What is the function of adrenergic receptors of target organs of the ANS?

Answer 10

mediate sympathetic effects

Question 11

What is the basic function of the sympathetic nervous system?

Answer 11

fight or flight

Question 12

What is the basic function of the parasympathetic nervous system?

Answer 12

rest and digest

Question 13

What is the effect of postganglionic fibers that release neurotransmitters at GCPRs?

Answer 13

initiates biochemical signaling cascade in the target tissue rather than sending action potential

Question 14

Where is norepinephrine released from?

Answer 14

released locally in tissues at most sympathetic postganglionic varicosities

from the adrenal medulla chromaffin cells into the bloodstream

Question 15

Where is epinephrine released from?

Answer 15

adrenal medulla chromaffin cells into the bloodstream

Question 16

What are the principal sympathetic neurotransmitters?

Answer 16

norepinephrine and epinephrine - but also can use ACh

Question 17

What is the location of, specific G-protein subunit, and effect of NE/E binding to alpha-1 adrenergic receptors?

Answer 17

location: smooth muscle.

Binds to Ga(q)

Effect is smooth muscle contraction

Question 18

What is the location of, specific G-protein subunit, and effect of NE/E binding to Beta-1 adrenergic receptors?

Answer 18

location: heart, juxtaglomerular cells

Binds to Ga(s)

Effect is promotion of contraction, increase HR

Question 19

What is the location of, G-protein subunit, and effect of NE/E binding to Beta-2 adrenergic receptors?

Answer 19

location: smooth muscle

Binds to Ga(s)

Effect is smooth muscle relaxation

Question 20

What is the effect of ACh binding to nicotinic receptors?

Answer 20

channels are opened and can depolarize the cell to 0mV

Question 21

What is the function of muscarinic ACh receptor M2 binding with released ACh?

What GCPR subunit/pathway is it associated with?

Answer 21

Couples to Ga(i), GBy

Function: Slows heart rate through (1) activation of a K+ channel via Gβγ subunits, leading to hyperpolarization, and (2) through inhibiting adenylyl cyclase via Gi, turning off the formation of the cAMP second messenger and reducing PKA activity

Question 22

What is the function of muscarinic ACh receptor M3 binding with released ACh?

What GCPR subunit/pathway is it associated with?

Answer 22

Couples to Ga(q).

Function: elevate intracellular Ca2+ via IP3 pathway.

This does:
1) smooth muscle contraction

2) stimulates glands to secrete
3) elevates nitric oxide (NO) production in endothelial cells, which leads to smooth muscle relaxation and therefore vasodilation

Question 23

What does AChE enzyme do?

Answer 23

catalyzes the inactivation of ACh via hydrolysis back into choline and acetate in the extracellular space of the synaptic terminal - prevents accumulation of ACh in the blood and therefore excess parasympathetic action

Question 24

What is the role of ATP in the ANS?

Answer 24

it activates purinergic receptor (ligand-activated non-selective cation channels) which initiates smooth muscle contraction in the arterioles and vas deferens

Question 25

What is the importance of NO in sexual arousal and how do ED drugs work?

Answer 25

NO potentiates blood flow during sexual arousal via stimulation of cGMP. ED drugs prolong the life of cGMP by stopping it’s breakdown by a PDE.

Question 26

How does nitroglycerine work?

Answer 26

improves coronary circulation by releasing nitric oxide, which diffuses into vessel smooth muscle to allow for vasodilation.

Question 27

How does the body respond to increase in arterial blood pressure?

Answer 27

1. afferent input: baroreceptors sense increased tension in the aortic arch and carotid sinus in increase their action potential firing rate.
2. action potentials are sent down baroreceptor axons to the medulla of the brainstem.
3. efferent outflow: parasympathetic NS is excited and sympathetic NS is inhibited, leading to decrease in blood pressure.

Question 28

How does the body respond to increase in arterial blood pressure?

Answer 28

1. afferent input: baroreceptors sense increased tension in the aortic arch and carotid sinus in increase their action potential firing rate.
2. action potentials are sent down baroreceptor axons to the medulla of the brainstem.
3. efferent outflow: parasympathetic NS is excited and sympathetic NS is inhibited, leading to decrease in blood pressure.

Question 29

How do baroreceptors counter orthostatic hypotension?

Answer 29

firing rate falls with decreased tension in aorta, action potentials transmitted to the brainstem decrease, sympathetic nervous system is excited and parasympathetic is inhibited

Question 30

What is the exception to the general rule of norepinephrine always being a sympathetic transmitter?

Answer 30

sweat glands

Question 31

What is the exception to the general rule that sympathetic pathway is a two-neuron pathway?

Answer 31

adrenal gland

Question 32

alpha-1 receptor pathway

Answer 32

norepinephrine binds to a1 -> activates G(q) -> PLC -> IP3 & DAG -> increase calcium, activation of PKC

Question 33

alpha-2 receptor pathway

Answer 33

norepinephrine binds to a2 receptor -> activates G(i) -> inhibits adenylyl cyclase -> cAMP decreased

Question 34

beta receptor pathway

Answer 34

norepinephrine binds to beat receptor -> activates G(s) -> stimulates adenylyl cyclase -> cAMP increases and PKAs are activated

Question 35

Alpha 1 location and effect

Answer 35

contract ANS smooth muscle, glands

Question 36

Alpha 2 location and effect

Answer 36

varied effect - presynaptic terminals of adrenergic nerves - inhibits NE release

Question 37

Beta 1 location and effect

Answer 37

increases HR and contraction, heart muscle, kidney juxtaglomerular cells, fat cells

Question 38

beta 2 location and effect

Answer 38

relaxation

smooth muscle, glands, enteric neurons

Question 39

Beta 3 location and effect

Answer 39

relaxation, prevention of urination

bladder, fat cells