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.
