postsynaptic

Postsynaptic refers to the cell that receives signals across a chemical synapse. In most chemical synapses, neurotransmitters released by the presynaptic neuron bind to receptors on the postsynaptic membrane, which is typically on a dendrite or soma of a neuron, or on a muscle cell at the neuromuscular junction.

Binding of neurotransmitter activates receptors on the postsynaptic membrane, which can be ion channels (ionotropic receptors) or receptors that signal through G proteins and other second messengers (metabotropic receptors). Ionotropic receptors produce rapid changes in membrane potential by opening ion channels, while metabotropic receptors modulate ion channels and intracellular signaling cascades more slowly. The net change in membrane potential is called a postsynaptic potential: excitatory postsynaptic potentials (EPSPs) usually result from inward Na+ or Ca2+ currents, whereas inhibitory postsynaptic potentials (IPSPs) often involve Cl− influx or K+ efflux.

The postsynaptic density is a protein-rich region beneath the postsynaptic membrane that contains receptors, ion channels, and signaling molecules. Scaffold proteins, such as PSD-95, organize receptors and link them to the cytoskeleton and to signaling pathways, influencing receptor localization and plasticity.

Plastic changes at the postsynaptic side underlie learning and memory, including long-term potentiation and depression. These involve receptor trafficking (e.g., insertion or removal of AMPA receptors), phosphorylation, and calcium-dependent signaling, with NMDA receptors playing a key role as coincidence detectors.

In the neuromuscular junction, the postsynaptic membrane of the muscle fiber bears nicotinic acetylcholine receptors; acetylcholine binding depolarizes the muscle membrane, triggering contraction. Dysfunction at the postsynaptic level is linked to various neurological and neuromuscular disorders.