18.5 Pacemaker Cells

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1

pacemaker cells contract

false

2

the sponteneously produced action is called

autorhythmic

3

where are pacemaker cells located?

throughout heart along special conduction pathways

4

what spreads the depolarizing current to cardiac muscle cells

gap junctions

5

pacemaker cells have an unstable resting membrane potential

true

6

the resting membrane potential of pacemaker cells is what?

-60 mV

7

pacemaker cells close K+ channels and open Na+ slowly to let sodium in

true

8

the cell become slowly depolarized by the Na+ voltage channels opening

true

9

the threshold of pacemaker cells is what?

-40mV

10

at the threshold what voltage gated channel opens?

Ca2+

11

for pacemakers to repolarize what is opened?

K+ voltage gated channels

12

conduction pathways run throughout the myocardium

true

13

what initiates the heart beat

the SA node

14

SA node

sinoatrial node

15

where are the SA nodes?

small mass of pacemaker cells in right atrial wall; inferior to the superior vena cava

16

how many impulses does the SA node generate a minute

75

17

The SA node generates a faster impulse than any other heart cell

true

18

the SA node is the true pacemaker of the heart

true

19

what does the Bachmann's bundle connect?

the right and left atria

20

the bachmann's bundle keeps both atria at synch

true

21

depolarization of the SA node causes what to happen?

atria to contract at the same time

22

there are gap junctions between atrial and ventricular myocardium

false

23

what does the internodal pathways connect?

SA node to AV node

24

where is the AV node located

in the interatrial septum, near tricuspid

25

What does the AV node do?

delays depolarization

26

AV node

atrioventricular node

27

how many impulses does the AV node generate per minute?

50

28

the AV node cannot run the heart if the SA is damages

false

29

the atrioventricular bundle connects what

AV node to ventricles

30

bundle of His

atrioventricular bundle

31

what is the only electrical connection between the atria and the ventricles?

atrioventricular bundle

32

atrioventricular bundle splits into right and left bundle branches

true

33

atrioventricular bundle does not continue on to form Purkinje fibers

false

34

purkinje fibers

depolarize the contractile cells of ventricles

35

subendocardial conducting network

purkinje fibers

36

purkinje fibers innervate papillary muscles

true

37

depolarization of pacemaker cells cause depolarilzation of cardiac muscles cells

true

38

what is the resting membrane potential in contractile cells

-90 mV

39

in resting membrane potential in contractile cells what channel is always open?

K+

40

what is the resting membrane potential for skeletal muscle?

-90 mV

41

during depolarization of contractile cells what is opened?

voltage gates fast Na+ channels, Na rapidly flow into cell

42

sarcolemma depolarizes to +30mV

true

43

at +30mV what opens in contractile cells?

voltaged gates slow Ca2+ channels

44

during repolarization of contractile cells what is opened?

voltage gated K+ channels and K+ leaves the cell

45

absolute refractory period

time when cell cannot depolarize again

46

the absolute refractory period is longer in cardiac muscle than skeletal muscle

true

47

the absolute refractory period prevents tetanic contractions such as cramps, spasms, and tremors

true

48

hypercalcemia

too much calcium

49

what does hypercalcemia cause?

prolonged and spastic heart contractions

50

hypocalcemia

low calcium levels

51

hypocalcemia reduces what?

the force of each heartbeat

52

hyperkalemia

high potassium levels

53

what does hyperkalemia do?

speeds up membrane repolarization disrupting heart rhythm

54

hypernatremia

blood Na+ levels are too high

55

what does hypernatremia prevent

the entry of calcium into myocardium

56

arrhythmia is a heart defect

true

57

arrhythmia

uncoordinated atrial and ventricular contraction

58

two types of arrhythmia

PAT and V-tac

59

PAT

paroxysmal atrial tachycardia; burst of atrial contractions

60

V-tac

ventricular tachycardia; rapid uncoordinated ventricular contractions

61

fibrillation

rapid and irregular contractions of cardiac muscles

62

what can treat fibrillation

defibrillator

63

what can lead to fibrillation

tachycardia

64

defibrillation does what?

restart entire electrical systems

65

ectopic focus

inappropriate region of heart controls rhythm

66

where can ectopic focuses appear

atria or ventricles

67

what are ectopic focuses caused by

  • ischemic damage to conduction pathways
  • stimulants
  • fever
68

what can ectopic focuses lead to

arrhythmia and fibrillation

69

a heart block is damage to what structure in the heart ?

AV node or AV bundle

70

first degree heart block

depolarization is delayed for too long

71

second degree heart block

only some of the impulses are transmitted

72

third degree heart block

no action potential pass to the ventricles

73

third degree heart block aka

complete heart block

74

asystole

period when heart fails to contract

75

asystole is when there are electrical signals from cardiac muscles

false

76

flatline

asystole