# What is the sum of the peak IPSP voltage change and the peak EPSP voltage change? d) What is the net change in synaptic potential when an EPSP and IPSP occur simultaneously? Why is your answer different from the simple sum of potentials in part c?

The membrane potential, Em, of a post-synaptic cell can be calculated from the following equation:

equation in attachment

where grest is the leakage current which maintains the resting potential, Erest is the normal resting potential, gE is the conductance due to excitatory post-synaptic channels (e.g., AMPA channels), ErevE is the reversal potential for the excitatory channels, gI is the conductance due to inhibitory post-synaptic channels (e.g., GABA channels) and ErevI is the reversal potential for the inhibitory channels (this equation comes from the equivalence circuit discussed in Lecture 13 & 14, slide 21). Assume grest = 1 milliSiemens, Erest = -65 mV, ErevE = -10 mV, ErevI = -70 mV.

a) If gE at the peak of the EPSP is 2 milliSiemens, what is the height of the EPSP without an IPSP (i.e., what is the change in potential from resting)?

b) If gI at the peak of the IPSP is 1 milliSiemens, what is the change in potential from resting?

c) What is the sum of the peak IPSP voltage change and the peak EPSP voltage change?

d) What is the net change in synaptic potential when an EPSP and IPSP occur simultaneously? Why is your answer different from the simple sum of potentials in part c?