How many EPSPs must be stimulated to produce action potential if all 5 ISPS are stimulated?

Question

Twenty neurons synapse with a single receptor neuron. Fifteen of the 20 neurons release neurotransmitters that produce EPSPs at the postsynaptic membrane, and the other 5 release neurotransmitters that produce IPSPs. Each time one of the neurons is stimulated, it releases enough neurotransmitter to produce a 2 mV change in potential at the postsynaptic membrane. If the threshold of the postsynaptic neuron is 10 mV, how many of the excitatory neurons must be stimulated to produce an action potential in the receptor neuron if all 5 inhibitory neurons are stimulated? (Assume that spatial summation occurs.)

Answer 1

Contrary to the above answer "All or none" refers to action potential propagation, not initiation which is mediated by electronic potentials created by EPSP / IPSPs in the soma.

If you assume spatial summation and each IPSP is -2mV then the total of all 5 inhibitory inputs summated is -10mV.

So to reach the 10mV threshold (assuming a resting potential of zero, which is of course not what you would get in real life but the question doesn't make sense unless you assume this) you need 20mV positive input, which would require 10 of the excitatory neurons to fire (if each produces a 2mV EPSP).

Answer 2

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Answer 3

Ever hear of the all or none.