In Figure 1 (above), the default settings were used with following values: initi
ID: 60113 • Letter: I
Question
In Figure 1 (above), the default settings were used with following values: initial resting or holding potential (HP) of -60 mV; stimulus amplitude of 100 mA/cm2; and stimulus duration of 0.1 msec. Note stimulus amplitude is measured in units of current (mA) per unit area and is displayed at the bottom of the figure. The conductances GNa and GK are displayed in lower traces. Observe the shape of the action potential, and correlate it with the rapid increase and decrease in Na+ conductance, and slower increase and decrease in K+ conductance.
Questions:
What is the magnitude of the action potential overshoot?
Why is the membrane potential following the action potential more negative than the resting (holding) potential?
What factors contribute to the increase and subsequent decrease in GNa and GK?
Explanation / Answer
a. The magnitude of action potential overshoot is about +45mV.
b. After the action potential, the negative potential is called as hyperpolarisation or undershoot. The voltage is more negative than the holding potential due to voltage-gated K+ channels remain open after reaching the resting potential.
c. The increase and decrease in the GNa and GK is due to the opening and closing of voltage-gated channels.
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