Describe how a sodium ion enters a voltagegated sodium ion c

Describe how a sodium ion enters a voltage-gated sodium ion channel. How does this channel act selectively for this ion?

Solution

When the cell membrane is at its resting membrane potential,the activation gates of the voltage gated sodium ion channnels are closed and inactivation gates are open.Voltage gated potassium ion channels are closed.Depolarization is caused when a stimulus makes the membrane potential to become more positive,leading to the opening of voltage gated sodium ion channels.On reaching the threshold many sodium channels are opened.Sodium ions move across the membrane causing depolarizaion.Voltage gated potassium ion channels also begin to open,but very slowly.Therefore depolarization takes place because more sodium ions diffuse into the cell than potassium ions diffuse out of it.As the membrane potential approaches maximum depolarization,the inactivation gates of the voltage gated sodium ion channels start closing and diffusion of sodium ions starts closing.Potassium ion channels remain open and potassium ions continue to diffuse out of the cell.The extra efflux of potassium ions causes the membrane potential to become slightly more negative than the resting value.After the potassium ions close the sodium and potassium ions establish resting membrane potential.

The voltage gated sodium ion channels consists of 4 subunits each having 6 transmembrane helices.Once actvated these helices open the pore.Two of the six helices are seperated by a loop that lines the pore and is responsible for the selective movement of sodium ions across the membrane