1. Molecular biology. A molecular structure within a cell or on the surface characterized by selective binding of a specific substance and a specific physiologic effect that accompanies the binding, e.g., membrane receptors for peptide hormones, neurotransmitters, antigens, and immunoglobulins.
2. Neurophysiology. Sensory nerve cells that respond to stimuli of various kinds. They are classified by the type of stimulus (chemoreceptor, mechanoreceptor, photoreceptor, thermoreceptor, and nociceptor) and by the location in the body (exteroceptor and interoceptor).