Question 1

Which structure is responsible for the mechanical and electrical connection between cardiac myocytes, allowing coordinated contraction of the heart?

Accepted Answer

Intercalated disk

Question 2

What is the primary function of gap junctions in cardiac muscle?

Accepted Answer

To allow electrical signals to pass rapidly between cells

Question 3

Which ion is essential for initiating contraction in cardiac muscle, and must enter from the extracellular space?

Accepted Answer

Ca2+

Question 4

During the action potential of an autorhythmic cell, which channel is responsible for the 'funny current' that initiates depolarization?

Accepted Answer

HCN channel

Question 5

Which equation best represents the relationship between membrane potential and ion permeability during the cardiac action potential?

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 6

Which of the following is TRUE regarding excitation-contraction coupling in cardiac muscle?

Accepted Answer

Ca2+ entry from the extracellular space is required for contraction

Question 7

A patient has a mutation that prevents phosphorylation of phospholamban (PLN). What is the most likely effect on cardiac muscle function?

Accepted Answer

Decreased rate of relaxation and reduced contractility

Question 8

Which of the following best explains why cardiac muscle cannot undergo tetanus (sustained contraction)?

Accepted Answer

The action potential duration is long, preventing summation

Question 9

Which step in the cross-bridge cycle is directly triggered by the binding of Ca2+ to troponin?

Accepted Answer

Tropomyosin shifts, exposing myosin binding sites on actin

Question 10

Which of the following statements about the length-tension relationship in cardiac muscle is correct?

Accepted Answer

A slightly stretched sarcomere increases Ca2+ sensitivity and force of contraction

Question 11

Which of the following is a direct effect of sympathetic stimulation on cardiac muscle contractility?

Accepted Answer

Phosphorylation of Ca2+ channels increases Ca2+ conductance

Question 12

During the plateau phase of the cardiac contractile cell action potential, which channels are open?

Accepted Answer

L-type Ca2+ channels

Question 13

Which of the following best describes the role of the SERCA pump in cardiac muscle relaxation?

Accepted Answer

It pumps Ca2+ back into the sarcoplasmic reticulum

Question 14

Which statement accurately describes the action potential in autorhythmic myocardial cells?

Accepted Answer

HCN channels open at -60 mV, allowing Na+ influx and gradual depolarization

Question 15

Which of the following is NOT a characteristic of cardiac myocytes?

Accepted Answer

Initiation of contraction by motor neurons

Question 16

Which process is responsible for Ca2+ induced Ca2+ release in cardiac muscle?

Accepted Answer

Activation of ryanodine receptors by Ca2+ influx through L-type Ca2+ channels

Question 17

A drug that blocks gap junctions in cardiac muscle would most likely result in which of the following?

Accepted Answer

Impaired electrical conduction between cardiac cells

Question 18

Which of the following best describes the effect of increased cytosolic Ca2+ in cardiac myocytes?

Accepted Answer

Increased cross-bridge formation and force of contraction

Question 19

Which equation describes the force generated by cardiac muscle as a function of sarcomere length and Ca2+ sensitivity?

Accepted Answer

$$F = k \cdot [Ca$$^{2+}$$] \cdot L$$

Question 20

Which of the following is a unique feature of cardiac muscle compared to skeletal muscle?

Accepted Answer

Requirement for extracellular Ca2+ entry for contraction

Cardiac Muscle: Structure, Function, and Physiology

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