postsinaptic

Postsynaptic refers to the cell or membrane that receives a signal at a synapse. In most chemical synapses, neurotransmitters released by the presynaptic neuron diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane. The postsynaptic cell is usually a neuron, with dendrites or the soma forming the receptive surface, but at the neuromuscular junction the postsynaptic element is a muscle fiber.

The binding of neurotransmitters to postsynaptic receptors produces a postsynaptic potential, a small change in the membrane potential of the postsynaptic cell. If receptors open cation channels, the membrane depolarizes, creating an excitatory postsynaptic potential (EPSP). If inhibitory receptors open channels that hyperpolarize the membrane, an inhibitory postsynaptic potential (IPSP) occurs. Receptors can be ionotropic, producing fast responses through ligand-gated ion channels, or metabotropic, initiating slower, longer-lasting effects via second messenger pathways.

Anatomically, the postsynaptic membrane contains a specialized region called the postsynaptic density, a protein-rich zone beneath the membrane that includes receptors, scaffolding proteins (such as PSD-95), and signaling molecules. This organization helps coordinate receptor signaling and downstream cascades.

Postsynaptic strength can be modified through plasticity, including receptor trafficking (insertion or removal of receptors like AMPA receptors) and changes in receptor sensitivity. Long-term potentiation and long-term depression are prominent forms of postsynaptic plasticity that contribute to learning and memory. In summary, the postsynaptic side determines how a synapse converts chemical signaling into electrical and biochemical responses.