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

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Flashcards in Lecture 09: Mechanisms Underlying Normal Heart Rate Changes (Hayward) Deck (22):
0

RR interval

R peak to R peak. Used to determine HR

1

sinus tachycardia

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

2

beta-1 adrenergic receptors on SA node bind what?

Norepinephrine from sympathetic postganglionics

3

sinus bradycardia

normal ECG with slow HR (<60 bpm)

4

2 possible causes of sinus bradycardia

Decreased sympathetic or increased parasym. input to SA node

5

Why does HR normally increase with inspiration?

increased pulmonary stretch afferent input during inspiration which inhibits parasympathetic output

6

Which ANS dominates HR?

Parasympathetic

7

Firing rates of pacemaker cells determined by 3 things:

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

8

Most important modulator of SA node

ANS

9

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

increases

10

increased intracellular cAMP ---> Pacemaker Na and Ca channels

make them more likely to open

11

how does beta-1 stimulation increase cAMP?

By activation of G protein

12

Increased pacemaker depolarization --> phase 4

makes phase 4 slope steeper

13

Increased pacemaker depolarization --> time required to reach AP threshold

decreases

14

activation of muscarinic receptors is linked with what protein?

inhibitory intracellular G protein

15

Inhibitory intracellular G protein 2 actions:

1) Decreases slops of phase 4 or spontaneous depolarization
2) increases time to threshold potential by increasing K+ conductance

16

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

Decrease

17

Muscarinic receptor binding --> probability K channels open

increase

18

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

parasympathetic

19

Ach --> potential?

Decreases potential

20

HR is normally determined by:

SA node intrinsic rate

21

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

phase 4

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