Zoo Psych Neuro 523 Problem Set 7 answers 2016 1 At a neuromuscular junction if the ratio of the conductance change for sodium and for potassium ions is one what is the reversal potential of the postsynaptic potential gNa gK Vrev EK Vrev ENa 1 math Vrev EK ENa 2 2 If you stimulated an inhibitory input to a neuron and observed no postsynaptic potential change how would you determine that a conductance change had in fact occurred If a conductance change has occurred it must mean that the voltage driving force on the ions involved must be zero i e Vm Eion so Vm Eion 0 in the VIE All you have to do is to change the resting potential by injecting current through an electrode and you should then see a PSP 3 This is a tricky one hint write out the first few terms of the Poisson distribution and study the relationship between successive terms how do the successive terms of the distribution differ from each other At a certain neuromuscular junction the average mepp is 0 7 mV When the nerve is stimulated 200 responses of amplitude 0 7 mV are observed and 100 of amplitude 1 4 mV How many times were there zero responses when the nerve was stimulated How many times were responses of 2 1 mV seen So I gave you n1 and n2 but you don t know N the total number of trials Following up on the hint you write no N po e m n1 N p1 e m m n2 N p2 e m m2 2 n3 N p3 e m m3 6 So you know n1 200 and n2 100 Rearranging the second term you get N n1 e m m Substitute into 3rd term and you get e m m n2 n1 e m m2 2 so n2 n1 m 2 So 100 200 m 2 So m 1 Therefore since p1 m po no n1 The number of zero responses is 200 Similarly since p3 p2 m 3 n3 n2 m 3 and the number of triples 33 3 4 What is the difference between a rectifying and a non rectifying electrical synapse How would you distinguish a rectifying electrical synapse from a chemical synapse A non rectifying synapse conducts current in either direction between the pre and post synaptic neuron while a rectifying synapse only conducts current in one direction There are numerous experiments that will help to distinguish electrical from chemical synapses I have included 4 here 1 Stimulate the presynaptic cell and compare the current input to the current of the PSP If the PSP signal is the same or amplified then the synapse is must be chemical However if there is an attenuation of the signal then the synapse is likely electrical 2 Remove external Ca ions Chemical transmission requires Ca ions for exocytosis of synaptic vesicles containing transmitter 3 Look for the presence of synaptic delay between the presynaptic stimulation and the postsynaptic response The presence of a 1 msec delay indicates a chemical synapse electrical synapses do not have a delay 4 Another way is to hyperpolarize cell B and observe the response in cell A If it is a rectifying electrical synapse then cell A should also hyperpolarize If it is a chemical synapse no change would be observed in cell A 5 When are depolarizing synaptic potentials inhibitory When the equilibrium potential of the ion is more positive than the resting potential but more negative than threshold