Synaptic Transmission 2 I. Postsynaptic Responses a. NT Activation of Postsynaptic (Ionotropic) Receptors i. ii. iii. When many channels open thus causing a macroscopic current event, the current is called the end plate current (EPC). Because the current caused by the EPC is inward, this depolarizes the neuron, also known as the EPP. The EPP in turn triggers a PSP by opening the voltage gated Na and K ion channels b. Reversal Potentials i. The potential where the EPC reverses (~0 mV in the NMJ) is called the reversal potential (RP) EPC is found using, =- EPC gAChVm Erev . Channels opened by ACh is insensitive to the membrane voltage, but instead depends on the # of channels opened by ACh, which in turn depends on the [ACh] in the synaptic cleft. Thus the membrane potential determines the direction and amplitude of the EPC solely through the driving force on the ions following through the channels opened by ACh. The same applies in the case of postsynaptic terminals and the PSC and PSP ii. At resting potential, the EPC is generated largely through Na influx. If the E
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