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Cardio Physiology > Original and Conduction of Cardiac Impulse > Flashcards

Original and Conduction of Cardiac Impulse Flashcards

1
Q

Where does excitation of the heart normally originates?

A

pacemaker cells in the SA node

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2
Q

Do the cells the SA node have a stable resting membrane potential?

A

No

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3
Q

What is the theshold resting membrane potential?

A

-40mV

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4
Q

In the pacemaker cells, does the permeability to K+ remain constant between action potentials?

A

No

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5
Q

What is the pacemaker potential?

A

. the slow depolarization of membrane potential to a threshold

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6
Q

What is the pacemaker potential due to?

A

DECREASE in K+ EFFLUX superimposed on a SLOW Na+ INFLUX (the funny current)

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7
Q

What happens once threshold is reached?

A

The RISING PHASE OF ACTION POTENTIAL (i.e. DEPOLARIZATION) is caused by activation of VOLTAGE-GATED Ca++ CHANNELS
Resulting in Ca++ INFLUX

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8
Q

What is the falling phase of action potential (repolarization) caused by?

A

activation of K+ CHANNELS

Resulting in K+ EFFLUX

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9
Q

What does cell to cell spread of excitation occur via?

A

gap junctions

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10
Q

What is the AV node and where is it?

A

-small bundle of specialized cardiac cells
ONLY point of electrical contact between atria and ventricles
-located at the base of the right atrium; just above the junction of atria and ventricles

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11
Q

Are AV node cells small or large in diameter?

A

small

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12
Q

Do AV node cells have fast or slow conduction?

A

slow

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13
Q

What does AV node conduction delay allow?

A

allows atrial systole (contraction) to precede ventricular systole

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14
Q

What allow rapid spread of action potential to the ventricles?

A

Bundle of His and network of Purkinje fibres

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15
Q

Is the action potential in contractile cardiac muscle cells different or similar from the action potential in pacemaker cells?

A

differs considerably

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16
Q

In the ventricular muscle action potential, what does the resting membrane potential remain at until the cell is excited?

A

-90

17
Q

What is the rising phase of action potential (depolarization) caused by?

A

by FAST Na+ INFLUX

18
Q

What does the fast sodium ion influx cause the action potential to rapidly become?

A

+30

19
Q

What is the depolarization stage known as?

A

Phase 0

20
Q

What is phase 1 of the Ventricular Muscle Action Potential?

A

Closure of Na+ channels and Transient K+ efflux

21
Q

What is phase 2 of the Ventricular Muscle Action Potential?

A

Mainly Ca++ influx

22
Q

What is phase 3 of the Ventricular Muscle Action Potential?

A

Closure of Ca++ channels and K+ efflux

23
Q

What is phase 4 of the Ventricular Muscle Action Potential?

A

Resting membrane potential

24
Q

What is the plateau phase and what is it due to?

A

When the membrane potential is maintained near the peak of action potential for a few hundred milliseconds (a unique characteristic of ventricular muscle action potential) and it is mainly due to INFLUX of Ca++ through voltage-gated Ca++ channels

25
Q

Does the vagus nerve supply a continuous or discontinuous supply to the heart?

A

continuous

26
Q

Under what conditions does vagal tone dominate?

A

resting conditions

27
Q

What parasympathetic stimulation supplies the AV and SA node?

A

Vagus nerve

28
Q

What does vagal stimulation do to slope of pacmaker potential?

A

decrease

29
Q

What do the sympathetic nerves to the heart supply?

A

AV and SA nodes, myocardium

30
Q

What on the ECG masks atrial repolarization?

A

QRS

31
Q

What is the PR interval?

A

largely AV nodal delay

32
Q

When on the ECG is diastole?

A

TP interval

33
Q

When is ventricular systole?

A

ST segment

34
Q

What do the T waves represent?

A

ventricular repolarization

Cardio Physiology (6 decks)

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