Question

Describe the role of potassium channels in the neuronal trigger zone.

Answer 1

Neuronal trigger zone is the area usually at the junction of the axon and cell body, the axon hillock where chemically regulated gates and the area with voltage regulated gates meet.K+ channels are responsible for maintaining the resting potential of a neuron as well as its re-polarization following an action potential.

When an excitatory neurotransmitter is released by the presynaptic neuron and binds to the postsynaptic dendrites, ligand-gated ion channels open, allowing sodium ions to enter the cell.This de-polarisation when sufficient ,opens the Na+ channels which initiate an action potential down the axon.As sodium enters the cell, the cell membrane potential becomes more positive.

At around +40 mV, the voltage-gated sodium channels begin to close and the voltage-gated potassium channels begin to open, moving potassium down its electrochemical gradient and out of the cell . The potassium channels exhibit a delayed reaction to the membrane repolarisation, and, even after the resting potential is achieved, some potassium continues to flow out, resulting in an intracellular fluid that is more negative than the resting potential, and during which no action potential can begin (refractory period). This refractory phase ensures that the action potential propagates down the axon and not back up it.

Voltage gated K+ chanels have an intracellular gate that serves to control the flow of ions through the pore.Upon membrane depolarization , these k+ channels transition occurs through multiple closed states before finally opening.Thus,K+ Channels undergo voltage-Dependent gating that involves resting,activated-not-open,open and inactivated states.

As a general principle , K+ channel opening promotes K+ efflux and causes cell membarane hyperpolarization .Conversely,K+ channel closing reduces K+ efflux and promotes cell membrane depolarization