Autonomic Nervous System

Question 1

what type of receptors are adrenoreceptors (both alpha and beta classes)?

Answer 1

GPCR

Question 2

contrast the effects of alpha1, alpha2, beta1, beta2, and beta3 adrenergic receptors (GPCR)

Answer 2

alpha1: Gq —> increase PLC (IP3, DAG) —> activate ligand-gated Ca2+ channels —> vasoconstriction

alpha2: Gi —> lower cAMP —> inhibits GI smooth muscle contractibility/glandular secretions/NT secretion (negative feedback)

beta1: predominately heart, Gs/cAMP —> increased chronotropy (heart rate) and inotropy (cardiac contractibility), renin secretion from renal JG cells (renin-angiotensin-aldosterone system)

beta2: in heart and vasculature, Gs/cAMP —> increased chronotropy (heart rate) and inotropy (cardiac contractibility), vasodilation, hepatic glycogen metabolism, glycogenolysis in skeletal muscle

beta3: Gs/cAMP —> lipolysis (adipose)

Question 3

chronotropy vs inotropy

Answer 3

chronotropy = heart rate
inotropy = cardiomyocyte contractile force

Question 4

as plasma levels of epinephrine increase, how does the affinity of epinephrine for the different types of adrenoreceptors change?

Answer 4

low plasma epi: higher affinity for beta1 (increased chronotropy and inotropy) and beta2 (vasodilation - skeletal muscle)

high plasma epi: higher affinity for alpha1 (vasoconstriction - arterioles) and beta1 (increased chronotropy and inotropy)

basically, there is a switch from vasodilation to vasoconstriction effects as plasma epinephrine levels rise, while heart rate/contractile force continue to be increased

Question 5

as plasma levels of norepinephrine increase, how does the affinity of norepinephrine for the different types of adrenoreceptors change?

Answer 5

low plasma norepi: higher affinity for alpha1 (vasoconstriction - arterioles) > beta1 (increased chronotropy and inotropy)&raquo_space;> beta2 (vasodilation - skeletal muscle)

high plasma norepi: higher affinity for alpha 1 (vasoconstriction - arterioles) and beta1 (increased chronotropy and inotropy)

basically with increased plasma levels of norepinephrine, there is a stronger chronotropy/inotropy effect

Question 6

in the sympathetic nervous system, preganglionic fibers are [shorter/longer] than postganglionic fibers

Answer 6

SNS: short preganglionic fibers (cholinergic - ACh), long post-ganglionic fibers (noradrenergic - NE)

Question 7

in the SNS, what signaling molecules and types of receptors are found in pre- and post-ganglion if fibers?

Answer 7

preganglionic fibers: cholinergic (ACh)

synapse on post-ganglionic fibers with cholinergic-nicotinic (N2R) receptors

post-ganglionic fibers: noradrenergic (norepinephrine)

synapse on effector tissues with adrenoreceptors (alpha and beta types)

Question 8

which adrenergic receptor is similar to the muscarinic M1/M3/M5 receptors in that it signals through Gq G protein to stimulate PLC?

Answer 8

alpha1 adrenergic: Gq —> PLC —> IP3/DAG —> vasoconstriction (arterioles)

muscarinic M1/3/5: Gq —> PLC —> IP3/DAG

Question 9

what is the function of the enzymes COMT and MAO?

Answer 9

COMT = catechol-O-methyl transferase
MAO = monoamine oxidase

these enzymes degrade adrenergics (NE/E) to decrease their level in the synapse

Question 10

what are the usual sources of epinephrine and norepinephrine, respectively, in the body?

Answer 10

most epi secreted from adrenal medulla (chromaffin cells)

most norepi secreted from postganglinoic sympathetic fibers

Question 11

modified post-ganglionic fibers within the adrenal medulla that secrete epinephrine into ciruclation

Answer 11

chromaffin cells

innervated by pre-ganglionic SNS fibers

Question 12

activation of which adrenergic receptors is responsible for facilitating each of the following sympathetic nervous system effects:
a. decreased GI motility/secretions
b. bronchiolar dilation
c. liver glycolysis, gluconeogenesis
d. skeletal muscle glycolysis, contractility
e. lipolysis (adipose)
f. chronotropy, inotropy
g. decreased insulin secretion (pancreas)
h. vasoconstriction

Answer 12

beta2:
a. decreased GI motility/secretions
b. bronchiolar dilation
c. liver glycolysis, gluconeogenesis
d. skeletal muscle glycolysis, contractility

beta3: e. lipolysis (adipose)

beta1: f. chronotropy, inotropy

alpha2: g. decreased insulin secretion (pancreas)

alpha1: h. vasoconstriction

Question 13

which provides a more rapid response, sympathetic or parasympathetic nervous system?

Answer 13

SNS is much more acute/rapid than PSNS

Question 14

in the parasympathetic nervous system, preganglionic fibers are [shorter/longer] than postganglionic fibers

Answer 14

parasympathetic: long preganglionic fibers (cholinergic - ACh), short post-ganglionic fibers (cholinergic - ACh)

Question 15

in the PSNS, what signaling molecules and types of receptors are found in pre- and post-ganglion if fibers?

Answer 15

preganglionic fibers: cholinergic (ACh)

synapse on post-ganglionic fibers with cholinergic-nicotinic receptors (N2R)

post-ganglionic fibers: cholinergic (ACh)

synapse on effect tissues with cholinergic-muscarinic receptors (CM, 5 isoforms)

Question 16

what enzyme degrades ACh in synapses?

Answer 16

cholinesterase

Question 17

what kind of drugs are atenolol, metoprolol, and propranolol?

Answer 17

beta blockers (indicated by “-olol” ending)

recall beta blockers are antagonists of beta adrenergic receptors

Question 18

what kind of drug is atropine?

Answer 18

atropine: antagonist of cholinergic-muscarinic (CM) receptors

recall CM receptors bind ACh and are found in effector tissues that PSNS cholinergic post-ganglionic fibers synapse on

Question 19

what are the 3 nuclei within the medulla through which ANS control of cardiac function originates?

Answer 19

1. NTS: nucleus of tractus solitarius
2. NA: nucleus ambiguous
3. DMV: dorsal motor nucleus of the vagus

DMV and NA are subdivided into cardioacceleratory center, cardioinhibitory center, and vasomotor center

Question 20

T/F: PSNS has no direct effect on vasodilation

Answer 20

TRUE: vasodilation occurs via less SNS signaling