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2. You record from a mammalian neuron that has two presynaptic inputs, A and B. You stimulate A and B individually and record depolarizing synaptic potentials that are 10 mV in amplitude. When you stimulate A and B at the same time you record a depolarizing potential of 5 mV. The resting potential of the neuron is -70 mV. 10 mV Stimulate A B 10 mV A Stimulate B Stimulate A and B at same time 5 mV Current injection Voltage recording Design an experiment and diagram and explain the results that let you conclude that A is excitatory and B is inhibitory. [6 marks]
outward outward Im Im 0 0 inward inward 3) A normal squid axon is maintained in seawater and a voltage clamp is applied. The membrane potential (Vm) is changed in a step-wise manner from the resting level Vm = -70 mV to Vm =0 mV, and the membrane currents (Im) were recorded. 0 -70 Vm (mV) outward Im 0 inward • Draw similar plots of membrane current for each of the following conditions. For each plot explain in one or two sentences why the graphs differ from the normal graph drawn above. [8marks-2 marks each] • Tetrodotoxin is added to the bath surrounding the axon. • A potassium channel blocker is added to the bath surrounding the axon • [Na+] outside is adjusted so that [Na+] outside = [Na+]inside • [K+]outside is adjusted so that [K+]ouside=[K+]inside a) b)
outward outward Im Im 0 0 inward inward c) d)