Question

Describe, in order, the events that create a local potential that (a) doesn’t result in an action potential, and (b) does result in an action potential.

Answer 1

Local potential is created when ligand binds to ligand gated ion channels in the cell membrane. Binding of this ligand causes movement of ions across the cell membrane. This leads to potential change occurring in the membrane called local potential change or simply local potential.

a) When efflux of positive charge ions such as K+ ion or influx of negatively charged ions such as Cl- ions occur then it leads to further negativity of the membrane taking the potential of the membrane away from the threshold voltage. As we know that action potential develops only when local potential changes are strong enough to bring the membrane potential to threshold voltage as at this voltage, voltage gated ion channels are opened causing deplarization and action potential generation occurs.

But here , the membrane potential has become more negative hence it won't be able to produce action potential.

b) When influx of positively charged ions such as Na+ ions or Ca++ ions occur due to opening of ligand gated channels. Then it brings the membrane potential towards threshold. As soon as the local potential brings the membrane potential to threshold, voltage gated channels open up causing depolarization and generation of action potential occurs