1) At which time point would the postsynaptic membrane potential from a second s
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Question
1) At which time point would the postsynaptic membrane potential from a second stimulus be the greatest? What molecular process can explain this phenomenon? 2) What are the four types of short-term synaptic plasticity? How do each of these affect the postsynaptic membrane potential of the second stimulus? Which of these lasts the longest? 3) How would the process of LTP be affected if NMDA channels were never blocked with Mg? How would it be affected if Mg could not be expelled from NMDA receptors? 4) What are silent synapses? Why are they silent, and how do they get converted to active synapses?Explanation / Answer
1). Depolarization is the phase of the influx of sodium ions, during which, the membrane potential becomes positive inside. If this membrane potential reaches a threshold level, then the action potential is generated. If the threshold potential is not reached, no action potential is generated, this is known as “all-or-none principle.”
The term “refractory period” refers to a period during the electrical activity of the heart. During refractory period, the nerve fiber does not respond to the stimuli because the sodium channels are in the closed state (depolarisation ends by the closure of sodium channels, without depolarization, the impulse cannot be transmitted).
Irrespective of the intensity of the stimulus, the nerve does not accept any impulses, this period is called as an absolute refractory period (the period from the peak of depolarization to the point of reaching resting membrane potential).
So, the postsynaptic membrane potential from a second stimulus is greatest after reaching the resting membrane potential (i.e. after absolute refractory period), because the sodium influx or depolarization only occurs after reaching the resting membrane potential. This phenomenon can be explained by the "all-or-none" principle.
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