Question

3. Many neurons contain "delayed K channels". Like voltage-gated Nat channels, these voltage-gated K+ channels open in response to a rise in membrane potential and then undergo inactivation. However, opening of the voltage-gated K channels lags behind opening of the voltage-gated Na channels. a) Why does neuronal function require the voltage-gated K channels to open more slowly than the voltage-gated Na channels? b) Compared to a neuron that lacks voltage-gated K channels, what differences would you expect in the shape of the action potential? c) Will the presence of voltage-gated K channels make the neuron more or less refractory to firing another action potential soon after the previous one?

Answer 1

Ans a. The activation kinetics of Na+ channels are faster than K+ channels. Basically, ion channels are protein pores in the membrane. Upon depolarization, the pore opens, which is a process with fast kinetics in Na+ channels and slower kinetics in K+ channels. K+ channel activation is in the order of 6 times slower than Na+ channel activation. The slower inactivation of K+ channels allows sufficient Na+ to flow in the cell for the depolarization phase of the action potential to develop.

Ans b.If neuron lacks voltage gated K+ channels than the action potential mechanism would stop because of eventual shortage of K+ ions in the extra cellular fluid of neurons which means there would be no depolarization possible which would possibly lead to delaying of or absence of reaction to a stimulus.

example: a person will not move his hand even if he is pin pricked.

Ans c.Yes,the presence of voltage gated K+ channels make the neuron more refractory to firing another action potential soon because as we know that due to voltage gated K+ channels depolarization of action potential develop. In depolarization channels allow sodium ions to flow from outside the cell into the cell. The sudden rush of sodium into the cell changes the electrical charge inside of the cell from negative to positive, which also changes the outside from positive to negative, allowing neurons to fire action potential in fast bursts permitting neuronal communication.