Question

Match the following events of an action potential to the most appropriate description. Answers will only be used once.

Question 1 options:

1234 Resets electrical conditions of the neuron following an action potential 1234 An exceptionally strong stimulus can trigger a subsequent action potential 1234 Voltage-gated sodium channels are open, and the neuron cannot respond to another stimulus 1234 The intracellular side of the neuronal membrane becomes less negative due to an influx of sodium ions

1. Relative refractory period 2. Repolarization 3. Absolute refractory period 4. Depolarization

Answer 1

Resets electrical conditions of the neuron following an action potential---------------- 2) Repolarization

An exceptionally strong stimulus can trigger a subsequent action potential-------- 1) relative refractory period

Voltage-gated sodium channels are open, and the neuron cannot respond to another stimulus--- 3) Absolute refractory period

The intracellular side of the neuronal membrane becomes less negative due to an influx of sodium ions-------- 4) depolarization

Explanation:

1. RESTING STAGE:
The membrane is in polarised state with potential in nerve about - - 85mV.
Sodium and potassium channels are closed. Na+ are more outside the cell; K+ are concentrated inside the cell. Potential difference: - 70mV.

2. Depolarization STAGE:
When local potential touches the threshold level it opens up sodium channel in the membrane causing abrupt rising of membrane potential towards positivity. It overshoot beyond the zero level and become positve.
This is because of entry of Positive Sodium ions into the cell

3.Stage of Repolarization:
Within fractions of second the sodium channel begins to close and potassium channels open up causing diffusion of positive potassium to outside the cell.
This results in decreasing of membrane potential towards negativity.

4. Resting Conditions Re-established
Na+ and K+ channels are closed. Sodium-potassium exchange pump moves Na+ out and K+ in. Resting potential difference: -85 mV

Absolute refractory period is the duration in action potential at which any strength of stimulus won't be able to elicit a new action potential. This period corresponds to initial phase of repolarization during which sodium inactivation gates are closed.

Relative refractory period is the duration in the action in which a strong stimulus will only be able to evoke an action potential.