Final answer:
Opening Na+ channels in a resting cell causes depolarization, as Na+ ions enter the cell and reduce the negative charge of the membrane potential, moving it towards zero. This is a key step in the initiation of an action potential.
Step-by-step explanation:
When Na+ channels are opened in a previously resting cell, the membrane potential will be affected by depolarization. This occurs because the concentration of Na+ is significantly higher outside the cell compared to inside, creating a strong concentration gradient that drives sodium ions into the cell. As sodium ions, which are positively charged, enter the cell, they decrease the negative charge of the resting membrane potential, moving it closer to zero. This shift in the membrane potential from the typical resting voltage of -70 mV towards a less negative value is known as depolarization.
Depolarization is crucial for the initiation of an action potential, which occurs following a stimulus that either opens a ligand-gated Na+ channel or a mechanically gated Na+ channel. Once the stimulus triggers these channels to open, Na+ enters the cell, and the resulting decrease in the negative charge inside initiates the action potential, a vital step in the process of neuronal communication and muscle contraction.