Question 1

Which structural feature of cardiac muscle cells is primarily responsible for resisting mechanical stress during heart contractions?

Accepted Answer

Desmosomes

Question 2

Compared to skeletal muscle, which of the following is TRUE about cardiac muscle fibers?

Accepted Answer

They are shorter, often branched, and may be uni- or bi-nucleate

Question 3

During the cardiac action potential, what is the primary cause of the 'calcium plateau' phase?

Accepted Answer

Sustained influx of calcium ions through L-type Ca$^{2+}$ channels

Question 4

Which equation best represents the Nernst equation for calculating the equilibrium potential of potassium ($K^+$) in cardiac muscle cells?

Accepted Answer

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

Question 5

A patient is given a drug that blocks L-type Ca$^{2+}$ channels in cardiac muscle. What is the most likely effect on the cardiac action potential?

Accepted Answer

Shortened plateau phase and reduced contraction strength

Question 6

Which of the following best explains why cardiac muscle cells have a longer refractory period than skeletal muscle cells?

Accepted Answer

The calcium plateau prolongs depolarization, preventing premature contractions

Question 7

Which neurotransmitter is released by the parasympathetic nervous system to decrease heart rate?

Accepted Answer

Acetylcholine

Question 8

In cardiac muscle, excitation-contraction coupling relies on which process for calcium release?

Accepted Answer

Calcium-induced calcium release from the sarcoplasmic reticulum

Question 9

Which of the following is a key difference between the action potentials of cardiac and skeletal muscle cells?

Accepted Answer

Cardiac muscle action potentials have a prolonged plateau phase due to calcium influx

Question 10

A researcher measures the resting membrane potential of a cardiac contractile cell and finds it to be approximately $-90$ mV. What is the main contributor to this negative resting potential?

Accepted Answer

High permeability to potassium ions

Question 11

Which of the following best describes the role of gap junctions in cardiac muscle tissue?

Accepted Answer

They allow for rapid electrical communication between adjacent cells

Question 12

If the autonomic nervous system upregulates cardiac muscle activity, which neurotransmitter is most likely involved?

Accepted Answer

Epinephrine

Question 13

Which of the following statements about cardiac muscle contraction is CORRECT?

Accepted Answer

It requires both surface membrane and sarcoplasmic reticulum calcium influx

Question 14

A mutation causes cardiac muscle cells to lack desmosomes. Which clinical consequence is most likely?

Accepted Answer

Increased risk of cell separation and arrhythmias

Question 15

Which of the following is a major anatomical difference between cardiac and skeletal muscle cells?

Accepted Answer

Cardiac muscle cells are often branched and connected by intercalated discs

Question 16

During the absolute refractory period of a cardiac muscle cell, which of the following is TRUE?

Accepted Answer

A second action potential cannot be initiated regardless of stimulus strength

Question 17

Which process is essential for relaxation of cardiac muscle after contraction?

Accepted Answer

Active transport of Ca$^{2+}$ back into the sarcoplasmic reticulum

Question 18

A patient with hyperkalemia (elevated extracellular $K^+$) is at risk for which change in cardiac muscle cell membrane potential?

Accepted Answer

Depolarization of the resting membrane potential

Question 19

Which of the following best explains why cardiac muscle cells do not require nerve stimulation to contract?

Accepted Answer

They possess intrinsic pacemaker activity

Question 20

Which of the following is a consequence of the long refractory period in cardiac muscle?

Accepted Answer

Prevention of tetanic contractions

Cardiac Muscle: Structure, Function, and Comparison to Skeletal Muscle

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