1. True or False : A postsynaptic potential is excitatory (EPSP) if the ion invo
ID: 55344 • Letter: 1
Question
1. True or False: A postsynaptic potential is excitatory (EPSP) if the ion involved has a reversal potential (Eion) that is more depolarized than the resting membrane potential (Vm or Vrest), even if that Eion is hyperpolarized to the threshold for firing an action potential.
2. An EPSP causes a depolarization of 15 mV on a proximal dendrite. At the same time, an IPSP causes a hyperpolarization of 10 mV in a different proximal dendrite.
Vm is -65 mV, and threshold for firing an action potential is -55 mV.
In this case, will an action potential be generated?
A. No, because the net effect on the membrane is -60 mV, which is below threshold.
B. Yes, because the EPSPs travel faster than IPSPs, so the hillock (trigger zone) will be stimulated to -50 mV, which exceeds threshold.
C. Maybe. We don't have enough information to answer this.
D. It depends on factors like "how much will the graded potentials decay before they arrive at the hillock". In short, if the axon hillock (trigger zone) is depolarized beyond -55 mV, the answer is "yes". If not, then "no".
A. No, because the net effect on the membrane is -60 mV, which is below threshold.
B. Yes, because the EPSPs travel faster than IPSPs, so the hillock (trigger zone) will be stimulated to -50 mV, which exceeds threshold.
C. Maybe. We don't have enough information to answer this.
D. It depends on factors like "how much will the graded potentials decay before they arrive at the hillock". In short, if the axon hillock (trigger zone) is depolarized beyond -55 mV, the answer is "yes". If not, then "no".
Explanation / Answer
1. True : A postsynaptic potential is excitatory (EPSP) if the ion involved has a reversal potential (Eion) that is more depolarized than the resting membrane potential (Vm or Vrest), even if that Eion is hyperpolarized to the threshold for firing an action potential.
2. An EPSP causes a depolarization of 15 mV on a proximal dendrite. At the same time, an IPSP causes a hyperpolarization of 10 mV in a different proximal dendrite.
Vm is -65 mV, and threshold for firing an action potential is -55 mV.
In this case, will an action potential be generated?
Answer. D. It depends on factors like "how much will the graded potentials decay before they arrive at the hillock". In short, if the axon hillock (trigger zone) is depolarized beyond -55 mV, the answer is "yes". If not, then "no".
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