q3 - 2confused2bdoctor

[ArchivalUser]

1. The onset of the QRS complex on surface ECG corresponds to which
action potential phase?
a. Phase I
b. Phase II
c. Phase III
d. Phase IV
e. Phase 0
2. The isoelectric ST segment on surface ECG corresponds to which
action potential phase?
a. Phase I
b. Phase II
c. Phase III
d. Phase IV
e. Phase 0
3. The T wave on the surface ECG corresponds to which action potential
phase?
a. Phase I
b. Phase II
c. Phase III
d. Phase IV
e. Phase 0

[ArchivalUser]

phase 0
phase II
phase III

[ArchivalUser]

agree

[ArchivalUser]

The answers are E, B, C. The surface ECG tracing, which is a representation of the electrical
activity of the heart, corresponds to the various phases of the ventricular
action potential. The QRS complex on surface ECG represents
ventricular depolarization. The intracellular activity during ventricular
repolarization is a rapid influx of sodium and corresponds to phase 0 of
the action potential. The isoelectric ST segment corresponds to continued ventricular depolarization and repolarization. This corresponds to
the plateau phase or phase II. This phase is mediated via slow calcium
channels. The T wave on surface ECG represents ventricular repolarization.
Intracellularly, this corresponds to phase III, during which potassium
rapidly exits the cells.