Question

Describe sequence of event rom initial stimules through to the resting state.

Answer 1

During the resting state, the cell (eg: nerve cell) is polarised. The interior of the cell is negatively charged, and it contains high concentrations of K⁺ ions. The exterior of the cell is positively charged, and it contains high concentrations of sodium ions. The resting membrane potential of a neuron is, -70 to -80mV (millivolts).

When any form of impulse strikes the nerve cell, it causes change in membrane potential by changing the ion permeability across the membrane. If the membrane potential reach threshold potential (the minimum potential difference to elicit a response), then the action potential is generated.

Electrophysiological events of nerve impulse conduction:

1. Depolarisation: It is the influx of sodium ions, and the membrane potential moves towards positive side, when the membrane potential becomes more positive inside i.e., approximately, +35 to +45mV, the process of depolarisation stops by the closure of sodium channels. This phase is followed by repolarisation.
2. Repolarisation: It is the efflux of potassium ions, and the membrane potential moves to the negative side. When it reaches normal resting membrane potential, the cell enters into the resting stage.
3. Refractory period: During refractory period, the nerve fibre does not respond to the stimuli because the sodium channels are in closed state (depolarisation ends by the closure of sodium channels, without depolarization, the impulse cannot be transmitted). Irrespective of the intensity of the stimulus, the nerve do not accept any impulses, this period is called as absolute refractory period (the period from the peak of depolarization to the point of reaching resting membrane potential).