Question

Briefly describe how the intrinsic excitability (i.e. Na_Vs & K_Vs) of a neuron determines its action potential waveform shape and inactivation period

Answer 1

in neuronal chemistry At rest, a typical neuron has a resting potential (potential across the membrane) of -60−60minus, 60 to -70−70minus, 70 millivolts. This means that the interior of the cell is negatively charged relative to the outside. so sudden change of this membrane potential we will get like that

a large enough depolarization event, perhaps resulting from multiple depolarizing inputs that happen at the same time, can lead to the production of an action potential. An action potential, unlike a graded potential, is an all-or-none event: it may or may not occur, but when it does occur, it will always be of the same size (is not proportional to the size of the stimulus).

• An action potential begins when a depolarization increases the membrane voltage so that it crosses a threshold value (usually around-55−55minus, 55 \text{mV}mVm, V).

• At this threshold, voltage-gated \text {Na}^+Na​+​​N, a, start superscript, plus, end superscript channels in the membrane open, allowing many sodium ions to rush into the cell. This influx of sodium ions makes the membrane potential increase very rapidly, going all the way up to about +40+40plus, 40 \text{mV}mVm, V.

• After a short time, the sodium channels self-inactivate (close and become unresponsive to voltage), stopping the influx of sodium. A set of voltage-gated potassium channels open, allowing potassium to rush out of the cell down its electrochemical gradient. These events rapidly decrease the membrane potential, bringing it back towards its normal resting state.

• The voltage-gated potassium channels stay open a little longer than needed to bring the membrane back to its resting potential. This results in a phenomenon called “undershoot,” in which the membrane potential briefly dips lower (more negative) than its resting potential.

• Eventually, the voltage-gated potassium channels close and the membrane potential stabilizes at resting potential. The sodium channels return to their normal state (remaining closed, but once more becoming responsive to voltage). The action potential cycle may then begin again.