Question

Describe how an action potential occurs in a neuron and any ions which are involved. Also explain the following graph at each point. | Voltage (mv) Time (ms)

Answer 1

It is a graph showing electrical changes in a nerve membrane.

numbering is done according to the given graph.

5-.it is the resting phase potential called resting membrane potential(-70mv).here the cell is more permeable to K+ions and relatively impermeable to Na+ions.inside the cell is negative and outside is positive,this is due to actvation of Na+K+ ATPase pump and k+ leaky channels(major).thus the cell sends 3Na+ outside in exchange of 2k+ inside also k+ ions leak out making inside of cell relatively negative in relation to outside.

Then there occours action potential when the cell is stimulated.Action potential curve is the graphical registration of electrical activity that occours in an excitable tissue.It shows 3 major parts.1.latent period,2.depolarization,3.repolarisation.

1.latent period is the period when no change occours in the electrical potential immediately after applying the stimulus.It is a very short period with duration of 0.5-1ms.When stimulus is applied,there is slight irregular deflection of base line for a very short period ,called stimulus artifact.slowly Na+ ions enter cell till it reaches a certain potential called threshold potential or firing level ,when rapid entry of Na+ions occur due to opening of Na+ channels.

2.After inital phase of slow depolarisation,rate increases suddenly and shoots up beyond the zero potential.it occuor after it reaches threshold potential,at which voltage gated Na+ channels are opened.

3. Repolarization_once depolarization is completed repolarization starts(initially rapid and later slow).As Na+channels are short lived they open and close rapidly and then k+ channels open leading to efflux of k+ ions.(all these channels are voltage gated).

4. it is the phase of hyperpolarization,occours due to more efflux of k+ ions out of cell. After some time cell again reaches its resting membrane potential.

While the cell is depolarised or repolarizing it doesnot respond to further stimuli called refractory period.