Refractory Period

Refractory periods are a short phase in time following an <a href="Action potential">action potential</a> where another action potential cannot be generated. There are two types of refractory periods:

1. The absolute refractory period is a period where it is completely impossible for another action potential to be activated, regardless of the size of the trigger. This is because the <a href="Sodium channels">sodium channels</a> are inactivated and remain that way until hyperpolarization occurs. In cardiovascular mechanism, this refractory period is sometimes called effective refractory period (ERP).
   http://www.cvpharmacology.com/antiarrhy/ERP
2. The relative refractory period is the period, that occurs during the undershoot phase, where an action potential can be activated but only if the trigger is large enough. This is because the sodium channels have been reactivated but it is a difficult process due to the counter-acting <a href="Potassium">potassium</a> flow Wayne M. Becker, Lewis J. Kleinsmith, Jeff Hardin. (2006) The World of the Cell, 6th edition, San Francisco:Benjamin Cummings.
   

The refratory period causes 3 things to occur.

• The brain will be able to percieve nerve impulses as seperated events since there is a time lag between them.
• The number of generated impulses or repetitive firing rate of a neuron will be limited in a given period of timeBruce, A, Et al. Molecular biology of the cell. (6th ed.). New York: Garland Science, Taylor &amp; Francis Group, LLC, an informa business; 2015. P622-623.
• The nerve impulses will only travel in one direction. This is because, as the <a href="Action potential">action potential</a> is moving forwards along axons, the <a href="Resting potential">resting potential</a> will be re-established behind it. However, not until this happens can a new action potential occur.