Describe the net flow of ionic current during the phases of the action potential. During what...

Describe the net flow of ionic current during the phases of the action potential. During what phase of the action potential does positive feedback occur.

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Expert Solution

* Action potential consists of 4 phases. Action potential is triggered by a graded potential. This graded potential depolarize the membrane till it reaches a threshold, Which will eventually help in activation of voltage gated Na+ channels .

In Phase 0,there will be rapid influx of Na+, later Na+ channels are inactivated, combined with efflux of K+. During this depolarisation, Voltage gated Na+ channels open because of electrical stimulus. As there is more amount of Na+ rush into the cell, positive Na+ ions causes raise of charge inside the cell from negative to positive. As the voltage gated Na+ channels get inactivated and voltage gated K+ channels open, action potential reaches its peak. After the threshold is reached, Action potential is produced ,as they described as all or nothing only after Threshold is reached, maximum response occurs. In second phase the efflux of K+ and influx of Ca+2 are balanced. After the cell is depolarized the voltage gated Na+ ion channels close. Raised positive charge inside cell causes K+ channels open, K+ ions move out of cell membrane and tries to reach the resting potential.

At the end of this phase, repolarization occurs because of K+ efflux, This is phase 3.

After phase 3, phase 4 resting potential is formed. In Phase 4, voltage gated Na+ channels close,K+ channels activate.

Na+ channel inactivation creates peak repolarization phase. K+ channel activation complete s it.

After every action potential there will be refractory period. It is divided into absolute and relative refractory period.

*In Phase 1of action potential, depolarisation, positive feedback occurs. When sodium ions enter, causing depolarisation membrane potential move toward Na+equilibrium potential.more Na+ channels open causing more influx of Na+ ions. This is also called regenerative process.

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Sydney Mullin answered 9 months ago

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