Refractory Periods MCQ - Practice Questions with Answers

Refractory Periods:

• At the peak of the action potential, all Na+ channels become inactivated.
• When Na+ channels are inactivated, they cannot be immediately opened again.
• Recovery from inactivation is a time- and voltage-dependent process and full recovery usually take about 3-4 ms. 
• Therefore, it takes about 3-4 ms for all Na+ channels to come out of inactivation in order to be ready for activation (opening) again. 
• The period from the initiation of the action potential to immediately after the peak is referred to as the absolute refractory period (ARP). 
• This is the time during which another stimulus given to the neuron (no matter how strong) will not lead to a second action potential. 
• Thus, because Na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials. 
• The absolute refractory period takes about 1-2 ms.
• After the absolute refractory period, Na+ channels begin to recover from inactivation and if strong enough stimuli are given to the neuron, it may respond again by generating action potentials. 
• However, during this time, the stimuli given must be stronger than was originally needed when the neuron was at rest. 
• The period during which a stronger than normal stimulus is needed in order to elicit an action potential is referred to as the relative refractory period.
• This ensures the one-way direction of an impulse from the cell body to the axon terminal