Question

What is caused by the inability of Na+ ion channels to open for several milliseconds after their

inactivation?

(1) hyperpolarization
(2) depolarization
(3) termination
(4) refractory period
(5) action potential

Answer 1

The refractory period is caused by the temporary inactivation of Na+ ion channels after an action potential, preventing immediate reactivation and ensuring proper transmission of neural signals.

Step-by-step explanation:

The inability of Na+ ion channels to open for several milliseconds after their inactivation leads to what is known as the refractory period. During an action potential, the voltage-gated Na+ channels open to allow Na+ ions to enter the cell, causing depolarization.

Following this peak depolarization, these channels become inactivated and enter a state where they cannot open again right away. This refractory period ensures that the action potential travels in one direction and prevents the neuron from becoming overly excitable.

There are two types of refractory periods: the absolute refractory period, where no new action potential can be initiated, and the relative refractory period, where a new action potential can only be initiated with a stronger than normal stimulus due to ongoing K+ outflow.

The refractory period thus plays a crucial role in the timing of action potentials.

Answer 2

The inability of Na+ channels to open after inactivation leads to the refractory period, which includes an absolute phase where no action potentials can be initiated and a relative phase where only a stronger stimulus can initiate an action potential.

Step-by-step explanation:

The inability of sodium (Na+) ion channels to open for several milliseconds after their inactivation is caused by the refractory period. During an action potential, there are two gates on the voltage-gated Na+ channel: an activation gate and an inactivation gate.

The inactivation gates close shortly after the cell depolarizes, preventing Na+ from entering the cell again. This period ensures that the action potential only travels in one direction towards the axon terminals.

The absolute refractory period is the time during which no new action potential can be initiated, regardless of the strength of a stimulus. This is due to the inactivation of Na+ channels.

The relative refractory period follows, during which a stronger than usual stimulus is required to initiate another action potential, as potassium (K+) is still exiting the cell.