When sodium channels are fully open, the membrane of the ventricular cardiocyte

There are choices for this question:

A. sharply hyperpolarizes 
B. sharply repolarizes 
C. sharply depolarizes 
D. plateaus 
E. has no reponse

The answer is "sharply depolarizes". When there is an opening of sodium channels, there will be an influx of sodium from the extracellular fluid into the cell (sodium are always bound to go inside the cell and this is regulated by the sodium-potassium pump). Sodium ions are cations and carries a positive charge, and when cations go inside the cell, depolarization occur (also when anions or negatively charged ions leave the cell, making the cell membrane more positive). 

Hyperpolarization occurs when anions go inside the cell (for instance, influx of chloride ions) or when cations leave the cell (for instance, efflux of potassium ions).

Attached is a figure representing the ventricular action potential.