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Flashcards in Physiology Deck (288)
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1

what is the name for the mechanism of the heart beating rhythmically in the absence of external stimuli?

autorhythmicity

2

where does excitation of the heart normally originate?

pacemaker cells in the sino-atrial node

3

where is the SA node located?

upper right atrium
(close to where the SVC enters the RA)

4

what is it called when a heart is controlled by the sino-atrial node?

sinus rhythm

5

why do cells within the SA node have spontaneous pacemaker potential?

they do not have a stable resting membrane potential so the drift through depolarisation spontaneously

6

what is the name of the slow depolarisation of membrane potential, that takes the potential to a threshold for the AP to occur?

pacemaker potential

7

what is the pacemaker potential (ie the slow depolaristation to a threshold) due to?

decreasing in K+ efflux
slow Na + influx
(resulting in an increasingly positive membrane potential)

8

what happens in a pacemaker cell once the threshold has been reached?
(the rising phase of action potential)

activation of voltage-gated Ca++ channels causing an Ca++ influx

9

what is the falling phase of the pacemaker action potential caused by?

activation of K+ channels
resulting in K+ efflux

10

why is there a short pause of the electrical impulse at the AV node?

to allow time for both atria to contract in order for co-ordination of systole

11

from SA node to the atria what is the process of excitation spread?

cell-to-cell spread of excitation via gap junctions

12

what are gap junctions?

low resistance protein channels

13

within the ventricles, what is the process of excitation spread?

cell-to-cell spread of excitation via gap junctions

14

where is the AV node located?

at the base of the right atrium
(just above the junction of atria and ventricles)

15

what should be the only point of electrical contact between atria and ventricles?

AV node

16

how do the cells within the AV node facilitate the pause that allows co-ordination of systole?

slow conduction velocity between them

17

what are the pathways by which the electrical impulse is spread from the SA node to the AV node?

internodal pathways
cell-to-cell spread (gap junctions)

18

what is the function of the bundle of his and the purkinje fibres?

allow rapid spread of action potential to the ventricles

19

what is the resting potential of ventricular muscle action potentials?

-90mV (until cell is excited)

20

what causes the rising phase of action potential within the ventricular muscle cell?

fast Na+ influx

21

what does the fast influx of sodium reverse the ventricular muscle action potential to?

+30mV
(from -90mV)

22

what phase is the rising phase of action potential within the ventricular muscle cell?

phase 0

23

what causes phase 1 of the ventricular muscle action potential?

closure of Na+ channels and transient K+ efflux

24

what phase is the plateau phase of the ventricular muscle action potential?

phase 2

25

what causes phase 2 (plateau phase) of the ventricular muscle action potential?

opening of Ca++ voltage gated channels and Ca++ influx
(with background K+ efflux causing it to balance out)

26

what causes phase 3 of the ventricular muscle action potential?

closure of voltage gated Ca++ channels and K+ efflux

27

what is phase 4 of the ventricular muscle action potnential?

membrane rests at resting membrane potential
(-90mV)

28

what is the unique characteristic of contractile cardiac muscle cell's action potential?

the plateau phase

29

what part of the nervous system influences the heart rate?

autonomic nervous system

30

what does sympathetic stimulation do to the heart rate?

increases heart rate