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First Year med - dundee > 75. The origin and conduction of the heart > Flashcards

75. The origin and conduction of the heart Flashcards

1
Q

What is the heart

A

electrically controlled muscular pump

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2
Q

what is autorhythmicity

A

the fact that the heart can beat rhythmically in the absence of external stimuli

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3
Q

where in the heart does the excitation normally originate to initiate the heart beat

A

In Pacemaker cells in the Sino-Atrial Node

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4
Q

where is the Sino-Atrial Node located

A

Upper Right Atrium (close to where the superior vena cava enters the right atrium)

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5
Q

A heart CONTROLLED by the Sino-Atrial node is said to be in …. …..

A

sinus rhythum

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6
Q

The cells in the SA NODE have ……. resting membrane potential

A

no stable

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7
Q

The cells in the SA node generate

A

regular spontaneous pacemaker potentials

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8
Q

The spontaneous pacemaker potentials takes the membrane to what

A

the threshold

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9
Q

when the threshold is reached, what is generated

A

Action potential - This results in the generation of REGULAR SPONTANOUS ACTION POTENTIALS in the SA nodal cells

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10
Q

what is the threshold for Intracellular Recording from SA Node Cell

A

-40mV (from an initial -60mV)

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11
Q

what is the pacemaker potential

A

the slow depolarization of membrane potential to the threshold aka -40mV (from an initial -60mV)

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12
Q

what causes the pacemaker potential

A
  1. The funny current - slow Na+ influx through HCN channels which are open when the cell is hyperpolarized (more negative)
  2. Decrease K+ efflux at the end of hyperpolarization period, less K+ leaves the cell which helps the inside of the cell to become less negative
  3. Ca2+ Influx also start to enter the cell, contributing to the gradual depolarization. (less negative)
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13
Q

once the threshold is reached it causes what

A

action potential (ie depolarization)

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14
Q

The RISING PHASE OF ACTION POTENTIAL (i.e. DEPOLARISATION) is caused…. HINT - what channels and what influx

A

by opening of long lasting (L-TYPE) voltage-gated Ca++ CHANNELS
Resulting in Ca++ INFLUX

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15
Q

what is the falling phase of action potentials called

A

repolarization

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16
Q

what is repolarization caused by

A
  • inactivation of L type Ca2+ channels
  • activation of K+ channels resulting in K+ efflux
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17
Q

cardiac excitement spreads from the Sino Atrial node to….?

A

Atrio-Ventricular Node

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18
Q

how does excitement spread cell-to-cell

A

Via Gap Junctions (and maybe Desmosomes but i will check!)

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19
Q

what is the AV node

A

a small bundle of specialized cardiac cells

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20
Q

where is the AV node located

A

base of the right atrium

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21
Q

what are the properties of the AV node cells

A

small in diameter, slow conduction velocity

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22
Q

spread of excitation: From SA node to AV node: mainly cell-to-cell conduction via gap junctions; but there is also some

A

Internodal Pathways

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23
Q

conduction is delayed where?

A

Av Node

24
Q

what does delay in conduction at the AV node allow

A

atrial systole (contraction) to proceed ventricle systole

25
Q

The Bundle of …..and its branches and the network of ……… allow rapid spread of action potential to the ventricles

A

His, Purkinje fibers

26
Q

Is the action potential in contractile cardiac muscle cells different to the action potential in pacemaker cells

A

YES

27
Q

the resting membrane potential remains at …………….mV until the cell is excited (cardiac muscle cell)

A

-90mV

28
Q

The rising phase (depoalrisation) is caused by what in cardiac muscle cells

A

fast Na+ influx

29
Q

The rising phase (depoalrisation) in cardiac muscle cells reverses the membrane potential to ……mV

A

+20 mV

30
Q

what is phase 0 of Contractile Myocytes Action Potential

A

Fast Na+ influx

31
Q

what is phase 1 of Contractile Myocytes Action Potential

A

closure of Na+ channels and transient (brief) K+ efflux

32
Q

what is phase 2 of Contractile Myocytes Action Potential

A

mainly Ca2+ influx (through L type Ca2+ channels)

33
Q

what is phase 3 of Contractile Myocytes Action Potential

A

closure of Ca2+ channels and K+ efflux

34
Q

what is phase 4 of Contractile Myocytes Action Potential

A

resting membrane potential

35
Q

which phase of Contractile Myocytes Action Potential is the Plateau phase

A

2

36
Q

what is the plateau phase of Contractile Myocytes Action Potential

A

the membrane potential is maintained near the peak of action potential for a few hundred milliseconds

37
Q

Plateau phase is unique to Contractile Myocytes Action Potential or Pacemaker cells

A

Contractile Myocytes Action Potential

38
Q

the falling phase is which stage of the contractile myocyte potentials

A

3

39
Q

It is possible to record the spread of electrical activity through the heart from the skin surface. What is this test?

A

Electrocardiogram (ECG)

40
Q

how does an ECG work

A

the wave of depolarisation and repolarisation moves across the heart and sets up electrical currents which can be detected by surface electrodes

41
Q

what are the standard ECG limb leads

A

Lead 1 - Right arm and left arm
Lead 2 - right arm and left leg
Lead 3 - Left arm and Left leg

42
Q

what is the P wave

A

atrial depolarization

43
Q

what is the QRS complex

A

Ventricular depolarisation

44
Q

what is the T wave

A

ventricular repolarisation

45
Q

what is PR interval

A

largley AV node delay

46
Q

what is the ST segment

A

Ventricular systole occurs here

47
Q

What is TP interval

A

diastole occurs here

48
Q

whats the order of ECG waves and intervals

A

P, PR Interval, QRS complex, ST segments, TP interval

49
Q

which nerve is the parasympathetic supply to the heart

A

Vagus

50
Q

what does the vagus nerve do on normal resting conditions

A

slows intrinsic heart rate from 100bpm to a normal resting heart rate of 70bpm

51
Q

finish the sentence. Vagus nerve supplies the ……….. and ……….. And what does the Vagus Nerve do when stimulated

A

SA Node and AV Node. Slows rate of firing from SA Node and increases AV Node delay

52
Q

when the vagus is stimulated the slope of pacemaker potential ………… and takes less/more time to reach threshold

A

decreases. More.

53
Q

cardiac sympathetic nerves supply what

A

SA Node, AV Node and Myocardium

54
Q

sympathetic stimulation does what?

A

increases the rate of firing from SA Node and decrease AV Node delay and increases force of contraction

55
Q

what neurotransmitter is acting on which receptors for sympathetic stimulation

A

Noradrenaline acting on beta 1 adrenoreceptors

56
Q

pacemaker potential reaches threshold slower/quicker.
Frequency of action potentials increase/decrease

A

quicker
increase

57
Q

whats the main difference between cardiac myocytes and pacemaker cells

A

Cardiac Myocytes:
Contraction and force
Respond to electrical impulses
Stable resting membrane potential with a plateau phase in their action potential.

Pacemaker Cells:
Heart rhythm
Spontaneous depolarization
Without a stable resting membrane potential.

First Year med - dundee (41 decks)

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