Q: Which equation best represents the Nernst equation for calculating the equilibrium potential of an ion, which is crucial for understanding cardiac muscle physiology?

$$E = \frac{RT}{zF} \ln \left( \frac{[\text{ion}]_{\text{out}}}{[\text{ion}]_{\text{in}}} \right)$$

Question 1

Which of the following best describes a key physiological difference between cardiac muscle and skeletal muscle?

Accepted Answer

Cardiac muscle cells are connected by intercalated discs, allowing synchronized contraction, while skeletal muscle cells lack these structures.

Question 2

Which ion plays a critical role in the plateau phase of the cardiac muscle action potential, distinguishing it from skeletal muscle?

Accepted Answer

Calcium ($$Ca^{2+})$$

Question 3

A patient is experiencing arrhythmias due to impaired electrical conduction in the heart. Which unique feature of cardiac muscle is most likely involved?

Accepted Answer

Intercalated discs containing gap junctions

Question 4

Which equation best represents the Nernst equation for calculating the equilibrium potential of an ion, which is crucial for understanding cardiac muscle physiology?

Accepted Answer

$$E = \frac{RT}{zF} \ln \left( \frac{[	ext{ion}]_{	ext{out}}}{[	ext{ion}]_{	ext{in}}} ight)$$

Question 5

During intense exercise, skeletal muscle can function anaerobically, producing lactic acid. Why is cardiac muscle less able to sustain anaerobic metabolism?

Accepted Answer

Cardiac muscle has a higher density of mitochondria and depends primarily on aerobic metabolism for ATP production.

Question 6

Which of the following best explains why cardiac muscle cannot undergo tetanus, unlike skeletal muscle?

Accepted Answer

Cardiac muscle action potentials have a prolonged refractory period due to the plateau phase, preventing summation.

Question 7

A researcher measures the resting membrane potential of a cardiac myocyte and finds it to be approximately $$-90 mV. $$Which ion is primarily responsible for this value?

Accepted Answer

Potassium ($$K^+)$$

Question 8

Which structure is present in cardiac muscle but absent in skeletal muscle, allowing for rapid transmission of electrical impulses between cells?

Accepted Answer

Intercalated discs

Question 9

If a drug blocks voltage-gated calcium channels in cardiac muscle, what is the most likely effect on the cardiac action potential?

Accepted Answer

Shortening of the plateau phase and reduced contraction strength

Question 10

Which of the following statements is true regarding the source of calcium for contraction in cardiac muscle compared to skeletal muscle?

Accepted Answer

Cardiac muscle uses both extracellular and intracellular calcium for contraction, while skeletal muscle primarily uses intracellular calcium.

Question 11

A patient with a mutation affecting gap junction proteins in cardiac muscle is most likely to experience which of the following?

Accepted Answer

Impaired synchronization of heart contractions, leading to arrhythmias

Question 12

Which of the following best describes the control of contraction in cardiac muscle compared to skeletal muscle?

Accepted Answer

Cardiac muscle contraction is initiated by the autonomic nervous system, while skeletal muscle contraction is initiated by the somatic nervous system.

Question 13

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

Accepted Answer

Cardiac muscle is protected from arrhythmias caused by rapid, repeated stimulation.

Question 14

Which of the following is a correct statement about the energy metabolism of cardiac muscle?

Accepted Answer

Cardiac muscle has a high density of mitochondria and can use both fatty acids and glucose for ATP production.

Question 15

Which of the following best explains why cardiac muscle cells are resistant to fatigue compared to skeletal muscle cells?

Accepted Answer

Cardiac muscle cells have a rich blood supply and abundant mitochondria, allowing continuous aerobic metabolism.

Question 16

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

Accepted Answer

Cardiac muscle contraction is initiated by pacemaker cells that generate spontaneous action potentials.

Question 17

A patient is given a drug that increases the permeability of cardiac muscle cell membranes to sodium ions. What is the most likely effect on the action potential?

Accepted Answer

The depolarization phase will be enhanced, leading to increased heart rate.

Question 18

Which of the following best describes the role of the sarcoplasmic reticulum in cardiac muscle compared to skeletal muscle?

Accepted Answer

The sarcoplasmic reticulum in cardiac muscle releases calcium only in response to extracellular calcium influx.

Question 19

Which of the following is a direct result of the presence of gap junctions in cardiac muscle?

Accepted Answer

Electrical impulses are rapidly transmitted between cardiac muscle cells, allowing coordinated contraction.

Comparison of Cardiac and Skeletal Muscle Physiology

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