Whether detecting a neurotransmitter in a synapse or a photon in the retina, the nervous system relies on specialized proteins that bind or respond to particular stimuli. These proteins are receptors. Binding or activation triggers conformational changes that open ion channels or initiate intracellular signaling cascades.

Ionotropic receptors are themselves channels and produce rapid electrical effects. Metabotropic receptors couple to G-proteins and generate slower, longer-lasting modulation. Sensory receptors in the periphery transduce mechanical, chemical, thermal, or electromagnetic energy into neural signals. The diversity of receptor subtypes allows the same transmitter to produce different effects in different cells or at different times.

Pharmacology is largely the science of receptor interaction: agonists activate, antagonists block, and allosteric modulators fine-tune responses. Genetic variation in receptors influences drug sensitivity and disease risk. Mapping receptor distributions across the brain has been a major achievement of molecular neuroscience.

• Protein that detects chemical or physical stimuli
• Can be ionotropic or metabotropic
• Transduces signals into cellular responses
• Primary target of most neuroactive drugs