Cardiac Conduction and Rhythm - (part of chapter 17) Flashcards

1
Q

What makes the heart muscle unique from other muscles?

A

It is capable of generating and rapidly conducting its own action potentials.

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2
Q

What are the parts of the cardiac conduction system?

A
Sinoatrial (SA) node
Internodal pathways
Atrioventricular (AV) node
AV bundle
Left and right bundles of the Purkinje system
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3
Q

What is the function of the SA node?

A

This is where the rhythmic impulse is generated.

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4
Q

What is the function of the internodal pathways?

A

They conduct the impulse from the SA node to the AV node.

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5
Q

What is the function of the AV node?

A

This is where the impulse from the atria is delayed before passing to the ventricles.

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6
Q

What is the function of the AV bundle?

A

This conducts the impulse from the atria to the ventricles.

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7
Q

What is the function of the left and right bundles of the Purkinje system?

A

They conduct the impulses to all parts of the ventricles.

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8
Q

What is the “pacemaker” of the heart?

A

The SA node.

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9
Q

What would happen if transmission of impulses through the AV node were blocked?

A

The atria and ventricles would beat independently of each other.

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10
Q

How does the delay of impulse conduction in the AV node provide a mechanical advantage to the heart?

A

It allows the atria to complete their ejection of blood before ventricular contraction begins.

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11
Q

What other parts of the cardiac conduction system (besides the SA node) have the ability to control the rhythm of the heart?

A

The AV node and the Purkinje system.

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12
Q

Why does the SA node control the heart under normal circumstances (even though other parts of the cardiac conduction system can do so)?

A

The discharge rate of the SA node is considerably faster than those of the AV node and the Purkinje system.

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13
Q

What are the three parts of an action potential (and what occurs during each)?

A

The resting - unexcited state during which the membrane is polarized (positive on the outside, negative on the inside).
Depolarization - a change in the direction of polarity (negative on the outside, positive on the inside).
Repolarization - reestablishment of polarity of the resting membrane potential.

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14
Q

Which three ions are the major charge carriers in cardiac muscle cells?

A

Sodium, potassium, and calcium.

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15
Q

What role do the charge carrying ions play in the generation of cardiac arrhythmias and conduction disorders?

A

Disorders of the ion channels along with disruption in the flow of these current-carrying ions are increasingly being linked to the generation of cardiac arrhythmias and conduction disorders.

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16
Q

What are the five phases of an action potential?

A
Phase 0 - the upstroke or rapid depolarization
Phase 1 - early repolarization
Phase 2 - the plateau
Phase 3 - rapid repolarization
Phase 4 - resting membrane potential
17
Q

What types of membrane ion channels do cardiac muscles have that contribute to the voltage changes that occur during the action potential?

A

Fast sodium channels
Slow calcium-sodium channels
Potassium channels

18
Q

What is responsible for the spikelike onset of the action potential during phase 0?

A

The opening of the fast sodium channels.

19
Q

What is the depolarization threshold?

A

The point at which the fast sodium gates open, causing the membrane potential to rapidly change from -90 mV to +20 mV.

20
Q

What causes the abrupt rise in membrane potential to cease at the onset of phase 1?

A

Inactivation of the fast sodium channels, which causes an abrupt decrease in sodium permeability.