Chapter 17 - The Heart Part 2

The atria contract

Which of the following happens immediately after the P wave?

AV node

Which of these structures conduct(s) action potentials the slowest?

SA node

Which part of the conduction system initiates the depolarizing impulse, which spreads throughout the heart?

AV node

Which part of the intrinsic conduction system delays the impulse briefly before it moves on to the ventricles?

SA node

Which part of the intrinsic conduction system normally initiates the depolarizing impulse that causes a heartbeat?

Purkinje fibers initiate spontaneous action potentials, which cause the ventricles to contract early.

A person notices his or her heart beat because he or she senses blood being pumped by the heart. Excessive caffeine intake can lead to irregular heart rhythms (arrhythmias) that patients perceive as "skipped beats." Given that caffeine is a stimulant, which of the following mechanisms best explains the reason for the feeling that the heart skipped a beat?

Gap junctions

Action potentials generated by the autorhythmic cells spread to the contractile cells through what structures in the membrane?

P wave

Contraction of the atria results from which wave of depolarization on the ECG tracing?

Bundle branches

Convey(s) the impulse down the interventricular septum

Purkinje fibers

Convey(s) the impulse throughout the ventricular walls

AV node

Delay(s) occurs here while atria contract

AV bundle

Electrical link(s) between atria and ventricles

The flow of positive ions from adjacent cells

In order to cause cardiac muscle contraction, the contractile cells must also depolarize. What causes the depolarization of the contractile cells?

Internodal pathways

Link(s) between the SA node and AV node

Potassium

One of the changes that occurs in the pacemaker potential (unstable resting membrane potential) in the SA node (an autorhythmic cell) is a decreased efflux of what ion?

Voltage-gated potassium channels

Repolarization of an autorhythmic cell is due to the opening of which channels?

SA node

Set(s) the pace for entire heart

Pressure in the ventricles increases

The AV valves close when?

Ventricular repolarization

The T wave of an ECG corresponds to?

So blood is forced upward, toward the semilunar valves

The anatomy of the intrinsic conduction system causes contraction of the ventricles to begin at the apex and move superiorly. Why is this important?

Pressure in the left ventricle falls below aortic pressure

The aortic valve closes when?

Pacemaker cells

The cells that rhythmically and spontaneously generate action potentials in the heart are called?

delayed; before

The electrical impulse is __________ as it passes through the AV node, because the atria need to contract __________ ventricles.

SA node

The main pacemaker of the heart is the?

End-diastolic volume

The maximum amount of blood in the ventricles at the end of the ventricular filling phase is called?

Ca2+ influx

The plateau phase of the cardiac action potential is due to?

Involve calcium voltage-gated channels

Unlike skeletal muscle action potentials, cardiac muscle action potentials?

Isovolumetric contraction

Ventricular systole begins during the __________ phase of the cardiac cycle.

Electrical activity in the heart

What does the ECG wave tracing represent?

Ventricular depolarization

What does the QRS complex represent in the ECG wave tracing?

Fast calcium

When threshold is reached at the SA node (an autorhythmic cell), what channels open causing further depolarization of the membrane?