Final answer:
When Na⁺ channels in an animal cell open, the membrane potential becomes less negative due to the influx of Na⁺ ions, leading to depolarization and potentially an action potential.
Step-by-step explanation:
When Na⁺ channels are opened in an animal cell, the membrane potential becomes less negative, a process known as depolarization. Initially, the cell has a resting membrane potential of around -70 mV, but upon opening the Na⁺ channels, Na⁺ ions rush into the cell due to a higher concentration outside compared to inside. This inrush of positive ions reduces the negativity inside the cell, moving the membrane potential toward zero. Eventually, the membrane potential can even become positive, reaching up to +30 mV during an action potential.
The change in membrane potential is due to electrical and concentration gradients that drive the Na⁺ ions into the cell. The subsequent influx of Na⁺ ions continues until the peak of the action potential, at which point Na⁺ channels close and K⁺ channels open, allowing K⁺ to leave the cell and leading to repolarization and eventually hyperpolarization.