Answer
Excitatory Post Synaptic Potential (EPSPs) and Inhibitory postsynaptic potentials (IPSPs) are potentials formed when neurotransmitters (ligands) bind to their specific binding sites in membranes of postsynaptic cells. In the generation of the EPSP the binding of the ligand causes a net in flow of Na+ ions through channels in the cell membrane. This results in a movement of the cell membrane potential closer to depolarization. In the generation of the IPSP the ligand also binds to its specific receptor; the result , particularly in the case of binding to metabotropic receptors linked to K+ ions is that K+ cations stream out of the cell. This makes the cell interior more negative with respect to the exterior, in other words, the IPSP generated hyperpolarizes the cell.
Work Step by Step
Many excitatory neurotransmitters bind to ionotropic receptors causing an outflow K+ ions and an inflow of Na+ (and Ca2+) ions. The large inflow of Na+ move the cell membrane potential towards threshold( depolarizes). In contrast most/many inhibitory neurotransmitters bind to metabotropic receptors. The opening of K+ channels that result and associated loss of K+ ions moves the cell membrane potential towards hyperpolarization .
