👉 Receptor proteins are specialized molecules found on the surface or inside cells that bind to specific signaling molecules, known as ligands, initiating a cellular response. These receptors act as the primary interface between the extracellular environment and the cell's internal machinery, translating external signals into biochemical actions. For instance, in the nervous system, neurotransmitter receptors on neuronal membranes detect signals from other neurons and trigger responses like muscle contraction or changes in mood. Receptors can be broadly categorized into ionotropic receptors, which directly control ion flow across the membrane, and metabotropic receptors, which initiate intracellular signaling cascades through second messengers. This dynamic interaction allows cells to respond precisely and efficiently to a wide array of stimuli, from hormones and neurotransmitters to light and temperature changes.
