Absolute Refractory Period

A refractory period is a period of time where the cells are resistant to depolarisation. There are 3 different refractory periods, firstly the absolute refractory period which is the part of the cardiac cycle where no further depolarisation can take place. Secondly it is the relative refractory period where depolarisation of the cells can occur but only if the stimulus is strong enough, and finally there is the diminished refractory period where the cells are still resistant to depolarisation but it can still occur even with a relatively small stimulus (Catalano, 2002).
The total duration of a compensatory break and an extra systole is equal to two cardiac cycles. Extra systole occurs when the heart receives a stimulus during diastole which causes an extra contraction to occur; it is then followed by a compensatory break which is a period of absolute refraction, where the muscle rests (Khurana, 2012).
A myogramme requires that needle electrodes be inserted into the muscle the electrical activity of the muscle is then displayed on a screen, showing the oscillating waves produced by the muscle and how the muscle reacts to a stimulus (Arthritis, foundation, 2017).
Vagus tonus refers to the degree of activity occurring within the parasympathetic nervous system, which may result in changes in heart rate, the vagus nerve is responsible for keeping the heart beating within normal ranges. Changes in vagal tone can be extremely dangerous (Wise Geek,