Final answer:
Increasing the external sodium ion concentration to 160mM leads to increased Na+ influx when sodium channels open, causing depolarization and a more positive membrane potential.
Step-by-step explanation:
When the external concentration of Na+ ions ([Na]out) is changed to 160mM, the membrane potential (Vm) of a cell is affected. The resting potential is typically around -70 mV due to the gradient maintained by the Na+/K+ pump and ion channels. If the concentration of Na+ outside the cell increases, more of these ions will enter the cell down their concentration gradient when sodium channels open.
This influx of Na+ causes depolarization, where the cell's membrane potential moves from -70 mV towards zero and may overshoot to reach positive values, potentially up to +30 mV during an action potential. This continues due to the strong concentration gradient for Na+, with further effects being dependent on other cellular mechanisms such as additional ion channel dynamics and membrane potential regulations.