Excitatory and Inhibitory Postsynaptic Potentials
Synaptic activation can either excite or inhibit a postsynaptic cell. During chemical synaptic transmission, neurotransmitters change postsynaptic membrane permeability to ions. For example, increased permeability to Na+ produces excitation, and increased permeability to K+ and Cl− produces inhibition. The former manifests as a depolarizing change in the transmembrane potential (EPSP), and the latter manifests as a hyperpolarizing change (IPSP). Each neuron receives input from many other neurons, so a membrane potential is a net influence of EPSPs and IPSPs. Excitatory neurotransmitters such as Glu and Asp produce EPSPs; inhibitory neurotransmitters such as GABA and Gly produce IPSPs. Drugs that enhance Glu or Asp action (or other wise enhance EPSPs) (eg, low nicotine doses) have excitatory effects in the CNS; drugs that enhance GABA or Gly action (or otherwise enhance IPSPs) (eg, diazepam) have inhibitory CNS effects.