Question 1

Which ion is primarily responsible for the rapid depolarization (Phase 0) in the action potential of contractile cardiac cells?

Accepted Answer

Na⁺

Question 2

During the plateau phase (Phase 2) of the contractile cardiac cell action potential, which of the following best describes the movement of ions?

Accepted Answer

Ca²⁺ enters the cell while K⁺ leaves, maintaining a relatively flat membrane potential.

Question 3

What is the correct sequence of the cardiac electrical conduction pathway?

Accepted Answer

SA node → AV node → Bundle of His → Purkinje fibers

Question 4

A patient is found to have a prolonged plateau phase in their cardiac action potential. Which ion's movement is most likely altered?

Accepted Answer

Increased Ca²⁺ influx

Question 5

During Phase 3 of the contractile cardiac cell action potential, which event occurs?

Accepted Answer

Ca²⁺ channels close and K⁺ efflux dominates, leading to repolarization.

Question 6

If the SA node fails, which structure typically takes over as the pacemaker of the heart?

Accepted Answer

AV node

Question 7

Which phase of the contractile cardiac cell action potential is characterized by the cell returning to its resting membrane potential?

Accepted Answer

Phase 4

Question 8

A drug that blocks Ca²⁺ channels would most directly affect which phase of the contractile cardiac cell action potential?

Accepted Answer

Phase 2 (plateau)

Question 9

Which equation best represents the Nernst equation for calculating the equilibrium potential of K⁺ during the cardiac action potential?

Accepted Answer

$$E_K = \frac{RT}{zF} \ln \left( \frac{[K^+]_{out}}{[K^+]_{in}} \right)$$

Question 10

A patient with hyperkalemia (elevated K⁺ in the blood) is likely to experience which change in their cardiac action potential?

Accepted Answer

Reduced repolarization due to decreased K⁺ gradient

Question 11

Which of the following best explains why the plateau phase is important in cardiac contractile cells?

Accepted Answer

It prevents premature contraction by prolonging the refractory period.

Question 12

If a mutation causes the Na⁺ channels to remain open longer during Phase 0, what is the most likely effect on the action potential?

Accepted Answer

Prolonged depolarization and increased risk of arrhythmia

Question 13

Which of the following is NOT a correct description of the cardiac electrical conduction pathway?

Accepted Answer

Impulse travels from AV node to SA node, then to Purkinje fibers.

Question 14

Which phase of the contractile cardiac cell action potential is most affected by a drug that increases K⁺ efflux?

Accepted Answer

Phase 3 (repolarization)

Question 15

A patient is given a medication that slows Ca²⁺ entry during the plateau phase. What is the most likely effect on cardiac muscle contraction?

Accepted Answer

Decreased force of contraction due to reduced Ca²⁺ availability

Question 16

Which of the following best describes the role of Purkinje fibers in the cardiac conduction system?

Accepted Answer

They rapidly distribute the electrical impulse throughout the ventricles for coordinated contraction.

Question 17

Which formula would you use to calculate the membrane potential ($$V_m) $$based on the Goldman-Hodgkin-Katz equation for multiple ions?

Accepted Answer

$$V_m = \frac{RT}{F} \ln \left( \frac{P_{K^+}[K^+]_{out} + P_{Na^+}[Na^+]_{out} + P_{Cl^-}[Cl^-]_{in}}{P_{K^+}[K^+]_{in} + P_{Na^+}[Na^+]_{in} + P_{Cl^-}[Cl^-]_{out}} \right)$$

Question 18

A patient with a blocked Bundle of His would most likely experience which of the following?

Accepted Answer

Delayed or absent ventricular contraction due to impaired impulse transmission

Question 19

Which phase of the contractile cardiac cell action potential is most responsible for the refractory period that prevents tetanus in cardiac muscle?

Accepted Answer

Phase 2 (plateau)

Cardiac Action Potential and Electrical Conduction System

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