Neuroscience problem
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 Garter
 Posts: 5
 Joined: Sat Mar 15, 2008 2:37 am
Neuroscience problem
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 what’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 add55 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!
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 what’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 add55 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!
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
Hint:the wikipedia entry could be helpful
Living one day at a time;
Enjoying one moment at a time;
Accepting hardships as the pathway to peace;
~Niebuhr
Enjoying one moment at a time;
Accepting hardships as the pathway to peace;
~Niebuhr
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