Choose Tutorial "The Na Action Potential"
Increase the time base ( Total # ( ms ) ) to 20 ms
Open a 2nd Stimulus Control Panel
Set the delay on the first panel to 0 ms.
leave duration and amplitude set to default
Set the delay on the second panel to 4 ms.
leave duration and amplitude set to default
Click on Reset & Run
Repeat this stimulation protocol with increases of the 2nd delay , in increments of ms
Describe what you observed , and propose a possible mechanism
When the second current injection is delayed by 10 milliseconds , it begins to decay non exponentially ,
indicating asdf
When the delay for IClamp[1] = 11 ms ,
another action potential can be triggered again
Repeat this stimulation protocol for 2nd delays of 4 , 5 , 6 , 8 , and 10 ms
increasing the 2nd stimulus amplitude to determine whether you can generate a 2nd action potential.
try doubling the amplitude repeatedly
Indicate what stimulus amplitude produced the most “action potential” like response.
2nd Delay ( milli second ) | Necessary Amplitude for AP ( nano Ampere ) |
---|---|
4 | 3.2 |
5 | 1.6 |
6 | 0.8 |
8 | 0.4 |
10 | 0.2133 |
Indicate what happened to threshold and action potential peak as the 2nd delay was increased.
Explain what could account for these changes in threshold and peak
the delay has to be at least long enough for sodium channels to inactivate and then reset to closed
the cell also has to wait on potassium channels to close and reset.
Set the 2nd stimulus delay to 10 ms
with an amplitude sufficient to generate an action potential
Select Keep Lines
Click on Reset & Run.
Now change the 1st stimulus to an amplitude of 0.5 nA and a duration of 8 ms.
Indicate what happened to the action potential triggered by the 2nd stimulus
it blocked it from happening
Indicate whether a 2nd action potential occurred after increasing the 2nd stimulus amplitude.
if you increase to around
Explain what events could have caused this to happen
most of the sodium channels are still inactivated
we got it to fire again because the first set potassium channels that opened during first action potential were still not closed
Close 2nd Stimulus Control Panel.
Set 1st stimulus amplitude to 0.0 nA
Set Total # ( ms ) to 30 ms
Increase Extracellular K ( mM ) in 1 mM increments
Explain what accounts for these electrical responses
first action potential fires
second action potential fires
the more you increase extracellular potassium , the more positive
this is generally going to move
making it easier to fire action potentials