Lecture 09: Mechanisms Underlying Normal Heart Rate Changes (Hayward)

Question 0

sinus tachycardia

Answer 0

normal ECG with fast HR (>150bpm in medium dog)

Question 1

RR interval

Answer 1

R peak to R peak. Used to determine HR

Question 2

beta-1 adrenergic receptors on SA node bind what?

Answer 2

Norepinephrine from sympathetic postganglionics

Question 3

sinus bradycardia

Answer 3

normal ECG with slow HR (<60 bpm)

Question 4

2 possible causes of sinus bradycardia

Answer 4

Decreased sympathetic or increased parasym. input to SA node

Question 5

Why does HR normally increase with inspiration?

Answer 5

increased pulmonary stretch afferent input during inspiration which inhibits parasympathetic output

Question 6

Which ANS dominates HR?

Answer 6

Parasympathetic

Question 7

Firing rates of pacemaker cells determined by 3 things:

Answer 7

1) rate of phase 4 spontaneous depolarization
2) maximum negative diastolic potential (max. neg. MP reached following repolarization)
3) threshold potential

Question 8

Most important modulator of SA node

Answer 8

ANS

Question 9

NE binding to beta-1 receptors –> probability of pacemaker Na and Ca channels to open via 2nd messenger system

Answer 9

increases

Question 10

increased intracellular cAMP —> Pacemaker Na and Ca channels

Answer 10

make them more likely to open

Question 11

how does beta-1 stimulation increase cAMP?

Answer 11

By activation of G protein

Question 12

Increased pacemaker depolarization –> phase 4

Answer 12

makes phase 4 slope steeper

Question 13

Increased pacemaker depolarization –> time required to reach AP threshold

Answer 13

decreases

Question 14

activation of muscarinic receptors is linked with what protein?

Answer 14

inhibitory intracellular G protein

Question 15

Inhibitory intracellular G protein 2 actions:

Answer 15

1) Decreases slops of phase 4 or spontaneous depolarization

2) increases time to threshold potential by increasing K+ conductance

Question 16

Muscarinic receptor binding –> probabilty Na and Ca channels open?

Answer 16

Decrease

Question 17

Muscarinic receptor binding –> probability K channels open

Answer 17

increase

Question 18

Which part of ANS might be linked to 2nd degree AV block?

Answer 18

parasympathetic

Question 19

Ach –> potential?

Answer 19

Decreases potential

Question 20

HR is normally determined by:

Answer 20

SA node intrinsic rate

Question 21

Funny Na+ channels are active in slow-type AP during which phase?

Answer 21

phase 4