Which type of receptor mediates fast synaptic signaling at many CNS synapses?

• A. Intracellular receptors.
• B. Ionotropic receptors.
• C. Metabotropic receptors.
• D. Nuclear receptors.

Answer: (B)

Fast synaptic signaling at many CNS synapses is achieved by ligand-gated ion channels that open directly when a neurotransmitter binds, allowing ions to flow and produce an immediate postsynaptic response. These are ionotropic receptors, which generate rapid changes in membrane potential within milliseconds. In contrast, metabotropic receptors (G-protein coupled) produce slower, indirect effects through second messenger systems; intracellular and nuclear receptors are involved in slower processes like gene transcription and are not responsible for the rapid opening of ion channels at synapses. Examples of ionotropic receptors include AMPA and NMDA receptors for glutamate, and GABA_A receptors for GABA, all mediating fast excitatory or inhibitory postsynaptic potentials.