Question

Define and describe depolarization, repolarization, hyperpolarization, and threshold.

Answer 1

Threshold: It is defined as the level to which membrane potential should depolarize to generate an action potential.

For example: Resting membrane potential of a neuron is -70mV and threshold is -55 mV. It actually means cell is more negative inside than outside. Therefore, if due to any stimulus, if there is depolarization of neuron till the level of -55mV, an action potential would be generated.

Depolarization: It refers to the process in which there is shift in electrical charge which results in less negative charge inside the cell.

For example: If RMP of neuron (-70mV) goes toward less negative side, this is depolarization. It is generally facilitated by opening of sodium channel in neuron and calcium channel in skeletal and pacemaker cell. There is influx of these charges which makes membrane potential less negative.

Repolarization: It refers to the reversal of depolarization and attainment of polarised state of membrane. It is facilitated by potassium channels which causes efflux of potassium and thus making the membrane more negative ie, polarized.

Hyperpolarization: When membrane potential decreases below resting membrane potential, it is called hyperpolarization.

For example: If during repolarization, membrane potential becomes more negative than -70mV, it is called hyperpolarization.