Term (recipient) for a specialized nerve cell that receives certain external and internal chemical (taste, smell) or physical (touch) stimuli and translates them into a form that the nervous system can understand. The receptor is the first member of the senses and serves as a biological sensor. Each receptor is designed exclusively for a very specific stimulus and, when stimulated, transmits electrical signals to the central nervous system. There they are interpreted (quasi translated) according to the brain region in which they arrive. A distinction is made between primary and secondary receptors. The primary receptors transmit heat stimuli, strong mechanical stimuli such as stretching, pressure or "sharpness". These include, for example, the touch receptors of the skin, which affect the sense of touch (i.e. trigeminal), and the olfactory cells in the olfactory mucosa (approximately 2 x 5 cm²) in the upper part of the nasal cavity, which affect the sense of smell (i.e. olfactory). Secondary receptors include those on the tongue and palate that affect the sense of taste (i.e. gustatory).