Absolute And Relative Refractory Period

1236 Words Feb 21st, 2016 5 Pages
1. a) Define absolute and relative refractory period in the myocardial action potential (2 marks)
Absolute refractivity period is a period where one action potential has been fired; another action potential cannot be fired no matter how strong the stimulus is. This is because the Na+ channels are inactivated. Relative refractory period follows the absolute refractivity period and is is a period where a stronger stimulus compared to the normal one is needed in order to depolarize the membrane, at this stage Na+ channels go from inactivated to a closed phase, at this point they are able to become activated, the peak is also at a lower amplitude than normal. b) Compare and discuss the relationship between the durations of the ventricular contraction and the ventricular action potential and refractory period using a diagram. Explain the significance of this relationship (4 marks) This diagram summarises the relationship between contraction and refractory period. The refractory period [RP] (yellow background) begins after the peak as the Na+ channels are closed and Ca2+ is opened, it also ends simultaneously with contraction (blue line); this is because after an action potential the Na+ channels would be activated therefore another action potential could be fired. The muscle starts to contract at phase 1 where the cell is depolarized; this is due to opening of Na+…
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