FIRST YEAR DAY 1

A 55-year-old man with hypokalemia presents with palpitations. The physician explains that the resting membrane potential of his cardiac myocytes is altered. Which ion channel is primarily responsible for maintaining the resting membrane potential in cardiac muscle?

• Fast Na+ channels

• L-type Ca2+ channels

• Inward rectifier K+ channels

• T-type Ca2+ channels

A patient is diagnosed with a genetic mutation affecting "Intercalated Discs." Which functional property of the heart will be most directly impaired?

• Ability to store calcium

• Rapid spread of action potentials (Functional Syncytium)

• Synthesis of ATP

• Duration of the absolute refractory period

During a laboratory experiment, a cardiac muscle fiber is stimulated. Unlike skeletal muscle, cardiac muscle cannot be tetanized. This is due to:

• Absence of T-tubules

• Long absolute refractory period

• Slow calcium sequestration

• Presence of gap junctions

A 60-year-old woman is prescribed a Calcium Channel Blocker. In the plateau phase (Phase 2) of the ventricular action potential, which of the following occurs?

• Rapid Na+ influx

• Slow Ca2+ influx balanced by K+ efflux

• Closure of all K+ channels

• Maximum K+ permeability

In the mechanism of "Excitation-Contraction Coupling," the trigger for calcium release from the Sarcoplasmic Reticulum (SR) is:

• Direct electrical stimulation of the SR

• Influx of Ca2+ through L-type channels (Calcium-induced calcium release)

• Entry of Na+ through fast channels

• Binding of Acetylcholine to the sarcolemma

A patient has severe hypercalcemia. What effect would this have on the heart's contraction?

• Spastic contraction

• Flaccid paralysis

• Increased heart rate

• Prolonged AV nodal delay

The "Self-Excitation" of the SA node (Phase 4) is primarily caused by the gradual opening of which channels?

• Fast Na+ channels

• Funny (If) sodium channels and T-type Ca2+ channels

• L-type Ca2+ channels

• Inward rectifier K+ channels

A patient is given a drug that increases the permeability of the SA node to Potassium (K+). What is the expected clinical effect?

• Tachycardia

• Bradycardia (Hyperpolarization)

• Increased contractility

• Ventricular fibrillation

The "Relative Refractory Period" of the cardiac cycle is defined as the time when:

• No stimulus, regardless of strength, can cause an action potential

• A supra-normal stimulus can trigger a second action potential

• The muscle is in Phase 0

• Calcium is being pumped back into the SR

A researcher notes that cardiac muscle T-tubules are larger than those in skeletal muscle and are found at the Z-lines. This anatomical feature is important because:

• It allows for anaerobic metabolism

• It facilitates the entry of extracellular Ca2+ necessary for contraction

• It houses the pacemaker cells

• It prevents the heart from overstretching