Electro chemical changes during action potential in heart
Spike potential (over shoot)
Spike potential (over shoot) is the steep change in the negativity of the cell from – 90 mV to more positivity of + 40 mV in the membrane potential due to rapid increase in the permeability of the Na+ ions to the interior of the cell.
Positive after potential
During repolarization, the membrane potential drops little more negative than the normal resting value of – 90 mV due to excess of K+ ion diffusion to out side the cell. This is caused by the prolonged opening of K+ channels for several milliseconds even after repolarization.
Resting membrane potential in cardiac muscle
The resting membrane potential in cardiac muscle is – 90 mV, but has long action potential (250 msec).
- S.A. node = – 50 to – 55 mV
- Cardiac muscle = – 85 to – 95 mV
- Conduction system = – 90 to -100 mV
- Ventricle muscle = -100 to -105 mV