Name (receiver) for a specialized nerve cell that absorbs certain external and internal chemical (taste, smell) or physical (key) stimuli and brings it into a form understandable to the nervous system. The receptor is the first member of the senses and serves as a biological sensor. Each receptor is designed exclusively for a very special stimulus and transmits electrical signals to the central nervous system when irritated. There they are interpreted (quasi translated) according to the brain region in which they arrive. One distinguishes between primary and secondary receptors. The primary impart heat stimuli, strong mechanical stimuli such as elongation, pressure or " sharpness ". These include, for example, the contact receptors of the skin, which are the sense of touch (ie trigeminal ), as well as the olfactory cells in the olfactory mucosa (about 2 x 5 cm ²) in the uppermost part of the nasal cavity, the sense of smell (this means olfactory ) affect. The secondary ones include the sense of taste (this means gustatory ) receptors on tongue and palate.