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What happens 1-2 milliseconds after the voltage gated Na+ channels open?
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What channels open during action potential? What do they do? Why?
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PhysiOEx Ex3Actvy5
Measuring absolute & refractory periods
| Question | Answer |
|---|---|
| What happens 1-2 milliseconds after the voltage gated Na+ channels open? | The channels inactivate meaning they no longer allow sodium to go through the channel. These channels cannot be re-opened by depolarisation for at least a few milliseconds so during this time fewer sodium channels can be opened. |
| What channels open during action potential? What do they do? Why? | Voltage gatedK+ channels, more slowly. They contribute to the re-polarisation of the action potential from its peak as more potassium flows out of this second type of potassium channel |
| Describe the phase of after-hyperpolarisation (or the undershoot) | The flux through extra voltage K+ channels the depolarisation of the membrane to threshold & it also causes the membrane potential to become transiently more negative than the resting potential at the end of an action potential |
| What 3 things make it harder for the 2nd action potential to be generated after the 1st action potential? | Voltage gated K+channels have opened, some voltage gated Na+ channels are inactivated & the efflux of K+ opposes a depolarisation towards threshold |
| What is the refractory period? | The time after an action potential where a 2nd action potential can be generated |
| Is the threshold for the 1st action potential the same or different from the 2nd action potential in a 60 msec interval? | The threshold for the 1st action potential is lower than the threshold for the 2nd action potential |
| What is the absolute refractory period? | The interval at which the 2nd action potential falls. The time in which no action potential can be generated regardless of the strength of the stimulus. |
| If you further decrease the interval between the stimuli, will the threshold for the second action potential change? | The threshold for the second action potential will be higher (requiring a larger depolarization). |
| Why is it harder to generate a second action potential during the relative refractory period? | A greater stimulus is required because voltage-gated K+ channels that oppose depolarization are open during this time. |
| What is the original threshold for this neuron? | A 20 mV depolarization to -50 mV. |
| As the interval between stimuli decreases, the depolarization needed to generate the second action potential | increases. |
| Judging from your results, what time period after the first action potential best describes the relative refractory period (the time when a second action potential can be generated only if the stimulus intensity is increased)? | 7.5 ms-60 msec |
| At what interval between stimuli did the second action potential fail, regardless of the stimulus intensity? What is the absolute refractory period for this neuron? | 3.75 msec answer to both Q's |
Created by:
meunid