Absolute And Relative Refractory Period

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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.…show more content…
The duration of contraction is between 0-150 ms, at this point the cell is at phase 2 (plateau phase), where Ca2+ is entering the cell due the opening of L type Ca2+ channels. The binding of Ca2+ to Troponin-C initiates contraction of the cardiac muscle. At phase 3 the Ca2+ channels close and slow K+ channels open . The relationship between refractory period and contraction is quite significant as they both occur simultaneously to ensure summation does not occurs. (Total 6 marks) 2. a) What is meant by an arrhythmia? Define bradycardia and tachycardia. (3 marks) Arrhythmia is defined as an irregular rhythm of a heartbeat; the heart can beat either too fast or too slow. Bradycardia is when the heartbeat is slower than normal (fewer than 60 BPM) in contrast to tachycardia where the heartbeat is faster than normal (more than 100 BPM). b) Give normal (or physiological) and pathological examples of each. (3 marks) Bradycardia could be caused by ageing which is a physiological cause, as the heart rate tends to slow down with age and during deep sleep where the heart rate may fall below 60 BPM. The main cause of Bradycardia may be to disease which is a pathological cause, such as hypothyroidism which slows down the electrical impulses throughout the heart. Other pathological causes could be due to damage of the heart’s electrical system; this includes Endocarditis which is an infection in the heart valves/inner lining Tachycardia could be caused by
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