AP2 18B HW

Which of the following structures collects the depolarization wave from the atria to pass it onto the ventricles?

AV node

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

AV node

Which of the following is NOT a difference between cardiac and skeletal muscle? Cardiac muscle does not use the sliding filament mechanism for contraction; skeletal muscle does. Cardiac muscle cells contain more mitochondria than do skeletal muscle cells. The plasma membranes of cardiac muscle cells interlock, but skeletal muscle fibers are independent. Cardiac muscle cells quickly die in the absence of oxygen; skeletal muscle cells are better able to adapt to oxygen deficiency.

Cardiac muscle does not use the sliding filament mechanism for contraction; skeletal muscle does.

Why are gap junctions a vital part of the intercellular connection of cardiac muscles? Gap junctions allow calcium to enter the cell, triggering calcium release from the SR. Gap junctions form strong intercellular connections. Gap junctions allow action potentials to spread to connected cells. Gap junctions contract when stimulated, strengthening the force of cardiac cell contraction.

Gap junctions allow action potentials to spread to connected cells. Gap junctions are a form of electrical synapse that allow action potentials to spread to connected cells. This property allows the signal to spread efficiently through the heart.

Which statement regarding cardiac muscle structure is accurate? Cardiac cells are long, cylindrical, and multinucleate. Cardiac cells possess few mitochondria. Myofibrils of cardiac muscle tissue vary in diameter and branch extensively. Cardiac muscle cells are independent of one another both structurally and functionally.

Myofibrils of cardiac muscle tissue vary in diameter and branch extensively.

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

P wave

Which portion of the electrocardiogram represents the depolarization wave received by the atria from the sinoatrial (SA) node?

P-wave

Which portion of the electrocardiogram represents the time during which the ventricles are in systole?

Q-T interval

During which portion of the electrocardiogram do the atrioventricular valves close, correlating with the first heart sound ("lub")?

R-S waves

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

SA node

The order of impulse conduction in the heart, from beginning to end, is __________.

SA node, AV node, bundle of His, bundle branches, and Purkinje fibers

Consider the following characteristics of the cells found in muscle tissue. Which feature is shared by both cardiac muscle and skeletal muscle? branched cells striations triads intercalated discs

Striations

Adding a chemical that reduces Na+ transport near the sinoatrial (SA) node would have what effect on the heart's intrinsic conducting system?

The SA node would depolarize less quickly, reducing the heart rate.

Suppose a patient develops a myocardial infarction that disables the sinoatrial node. Would the heart still pump blood to the aorta and the pulmonary trunk?

Yes, because the atrioventricular node will still stimulate ventricular systole.

The P wave on an electrocardiogram represents __________.

atrial depolarization

What does the ECG wave tracing represent?

electrical activity of the heart

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

fast calcium

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

gap junctions

What structures connect the individual heart muscle cells?

intercalated discs Intercalated discs connect the heart muscle cells. They include desmosomes (anchoring junctions) and gap junctions (communicating junctions).

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?

potassium

Specifically, what part of the intrinsic conduction system generates the original stimulus that reaches the atrioventricular (AV) node, allowing it to conduct impulses to the atrioventricular bundle?

sinoatrial (SA) node

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

the flow of positive ions from adjacent cells

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

ventricular depolarization

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

voltage-gated potassium channels