# Neuroscience problem

• Author
Posts
• #12476
inquilinekea
Participant

Hm so I’m having difficulty in answering this question. This is what I have so far:

1. The problem statement, all variables and given/known data

Consider a neuron with resting potential of -65 mV and threshold of -55 mV. It receives two
synaptic inputs with similar synaptic conductances, one with reversal potential of -10 mV and the
other with reversal potential of -58 mV. Draw the predicted postsynaptic response (change in
membrane potential) to stimulation of each synapse alone, and then to simultaneous stimulation of
both synapses. Briefly explain whatâ€™s going on and why the results might at first be confusing.

3. The attempt at a solution

So the neuron will reach an action potential at -55 mV. So if the neuron gains 10 mV, it will depolarize and reach an action potential. Now, how will the synaptic inputs affect the neuron? Input 1 might have a reversal potential of -10 mV, but that doesn’t say how much current it sends to the neuron, nor does it say the proportion of total positive/negative ions in the input compared to that of the neuron. So that confuses me. How do we add potentials? Do we just take some average of the resting potential of the neuron with the reversal potential of the inputs? Which would be sort of like adding up concentrations or ratios. Or do we add-55 to -10 and -55 to -58? Ions sum up additively (and don’t involve taking ratios) but I highly doubt the question wants me to say that since then there would just be hyperpolarization and no action potential for either input.

Thanks!

• #96051
mith
Participant

I think the reversal potential means the neuron potential becomes -10mV or -58mV no adding needed. So in case 1 the threshold is breached and it fires, and in case 2 it’s not fired (-58<-55). However, when you "add" them, they can’t both be simultaneously true i.e. the potential can’t be -58 and -10 at the same time…in this case you’d have to look back at the definition of reverse potential and see what exactly is happening.

Hint:the wikipedia entry could be helpful