Question

1. Which of the following statements is false?

a. The action potential of a cardiac contractile cell has a plateau.

b. The action potential of a cardiac contractile cell has three phases.

c. The action potential of a cardiac contractile cell has a gradual depolarization.

d. The action potential of a cardiac contractile cell returns to rest.

2. The electrical axis of the heart corresponds to:

a. The conduction of the heart

b. The cardiac contractile cell action potential

c. The cardiac nodal cell action potential

d. The orientation of the heart

Answer 1

Ans1:- b)The action potential of a cardiac contractile cell has three phases.

There are five cardiac action potential phases, numbered 0 through 4 .

Phase 0 is depolarization of the membrane and the opening of "fast" (i.e., high-flow) sodium channels. Potassium flow also decreases.

Phase 1 is partial repolarization of the membrane thanks to a rapid decrease in sodium-ion passage as the fast sodium channels close.

Phase 2 is the plateau phase, in which the movement of calcium ions out of the cell maintains depolarization. It gets its name because the electrical charge across the membrane changes very little in this phase.

Phase 3 is repolarization, as sodium and calcium channels close and membrane potential returns to its baseline level.

Phase 4 sees the membrane at its so-called resting potential of −90 millivolts (mV) as a result of the work of the Na+/K+ ion pump. The value is negative because the potential inside the cell is negative compared to the potential outside of it, and the latter is treated as the zero frame of reference. This is because three sodium ions are pumped out of the cell for every two potassium ions pumped into the cell; recall that these ions have an equivalent charge of +1, so this system results in a net efflux, or outflow, of positive charge.

From above explaination it is clear that all other options are correct.

Ans2:- a). The conduction of the heart

The mean QRS axis refers to the average orientation of the heart's electrical activity.

normal heart axis is between –30° and 90°. If the axis is more positive than 90° it is referred to as right axis deviation. If the axis is more negative than –30° it is referred to as left axis deviation.