What characteristic makes voltage gated Na channels open quickly?

Voltage-gated sodium channels are integral membrane proteins that play a crucial role in the generation and propagation of action potentials in excitable cells, such as neurons and muscle cells. The characteristic that allows these channels to open quickly is related to their responsiveness to changes in membrane potential.

When there is a small change in voltage, typically from a resting potential to a threshold potential, these channels undergo a conformational change due to the positive feedback mechanism triggered by the initial depolarization. This change in voltage leads to an all-or-nothing response where the channels open rapidly, allowing sodium ions to flow into the cell. This influx of sodium ions contributes to the rapid depolarization phase of action potentials.

A large change in voltage would not be characteristic of the initial activation compared to the threshold that smaller changes begin. The absence of electrical charge would not influence the behavior of the sodium channels since they are dependent on voltage difference for their operation. Additionally, while the concentration of sodium ions is necessary for the function of the channels, it is the change in voltage that directly triggers the quick opening of the channels. Thus, a small change in voltage is the key characteristic that leads to the rapid opening of voltage-gated sodium channels.