Looking simulations A and B, the membrane

Looking at stimulus C, again, only one action potential was
produced for that of the first stimulus. Conversely, the value for the
depolarisation produced for the second stimulus in simulation C is greater than
the values produced in simulation A and B, which was due to the fact that for
simulations C and D, the delay between the two stimulations was 7 ms instead of
4ms as presented in simulations A and B.

 

For simulation D, there were two action potentials produced.
The first action potential had a larger peak than that the second. This
indicated that there was a refractory period for the second simulation, however
this refractory period would be known as the relative refractory period,
whereas previously in simulations A and B, the membrane was in the absolute
refractory period. The difference between these two periods is that an action
potential is unable to be triggered in any way during the absolute refractory
period, however, there is the possibility of an action potential being produced
in the relative refractory period. This is because for the relative refractory
period, a large enough stimulus will allow the membrane to reach threshold
potential, whereas changing the intensity of the stimulus in the absolute
refractory period cannot sufficiently depolarise the membrane. So, for
simulation D, the second stimulus, which increased from 50mA/cm2 to 100 mA/cm2, was large enough
to depolarise the membrane fully and thus trigger an action potential.

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Referring back to the fact that comparatively,
simulations C and D also had a delay of 7 ms rather than the 4ms delay for simulations
A and B, this allowed for a greater amount of time for the concentration
gradients of the cell to return to resting potential after the refractory
period and hyperpolarisation, and thus allow for another action potential as
sodium channels can then be activated more efficiently to fully depolarise the
membrane. This is evident by the fact that a greater value for depolarisation
was measured in the second stimulus for simulation C and two action potentials
were produced in simulation D, whereas only one action potential was produced
for both simulation A and C.

 

Q6. As an action potential was not produced, latency would not be able to be
measured as it was not reached, similar to how an action potential was not
reached. The infinity symbol is used to quantify an amount that cannot be
measured. In this case it would therefore be suitable to refer to the latency
with infinity as the value for latency cannot be measured.

 

Q7. From my
results, it was clear that a minimum threshold voltage (mV) was required to
trigger an action potential. The recorded threshold voltages were fairly
similar in value and all ranged from -56 to -68, thus showing that an action
potential could only be reached if these threshold potentials were reached for
each stimulus. This would therefore indicate that action potentials are
threshold phenomena.

 

Q8. The values
for amplitude of the action potentials that I recorded during the experiments
were all very similar, thus reinforcing the ‘all or nothing principle’ of
action potentials which states that an action potential is either triggered or
is not and once it has been triggered, each action potential has the same size.
As the amplitudes, I recorded were all similar, this would align to the ‘all or
nothing principle’.

 

Q9. From Graph 1,
it can be see that in general, as the stimulus strength (mA/cm2)  increased, the latency (ms) of the action
potential decreased. Each stimulus duration created a curve besides that of 0.5
ms, that all otherwise showed that as stimulus strength increased, latency
decreased. The 0.5 ms stimulus duration did not produce a curve as there was
not enough data for this variable. The curve produced by the 1 ms stimulus duration
presented a much steeper decline for the trend, while the 2 and 5 ms stimulus
durations had more gentle slopes.

 

Q10. From Graph
2, it can be seen that as stimulus duration (ms) increases, latency (ms)
remains constant.  From 2ms onwards, all the
strengths remain fairly constant. The graphs produced for that of 7 and 10 mA/cm2 present some declines in their latencies from
1-2 ms, with 7mA/cm2  having a slightly steeper
decline than that of 10mA/cm2 .