In an experiment you are studying a neuron that receives synaptic inputs from two other neurons: one from neuron A and one from neuron B. Synaptic transmission from neuron A opens Ca2+ channels in the postsynaptic neuron, whereas neuron B opens Cl– channels. Assume that ECa = +200 mV, ECl = –80 mV, and Vr = –60 mV. Consider the effect of input from neuron A.

a.   Consider the effect of input from neuron A. Draw the current flow you would expect to record in the postsynaptic neuron when Vm is set to the following values with the voltage-clamp technique: 100 mV, 50 mV, 0 mV, –50 mV, and –100 mV. Draw a separate graph for each value of Vm. [0.5

b.   Does the input from neuron A depolarize or hyperpolarize the postsynaptic neuron when it is at Vr? Explain the reason for your answer.

c.   Now consider the input from neuron B. Draw the current flow you would expect to record in the postsynaptic neuron when Vm is set to the following values with the voltage-clamp technique: –60 mV, –70 mV, –80 mV, –90 mV, and –100 mV.

d.   Does the input from neuron B depolarize or hyperpolarize the postsynaptic neuron when it is at Vr? Explain the reason for your answer. [

e.   Suppose the results from the experiment indicate that the neuron receives synaptic input from a third neuron (neuron C) that releases a novel neurotransmitter. You perform a voltage-clamp experiment and discover that the reversal potential for this new neurotransmitter is –55 mV. Is this substance excitatory or inhibitory at Vr? Explain then reason for your answer.