Term (recipient) for a specialized nerve cell that absorbs certain external and internal chemical (taste, smell) or physical (tactile) stimuli and brings them into a form that the nervous system can understand. The receptor is the first link 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 it is stimulated. 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 transmit heat stimuli, strong mechanical stimuli such as stretching, pressure or " sharpness ". These include, for example, the touch receptors on the skin, which use the sense of touch (i.e. trigeminal ), as well as the olfactory cells in the olfactory mucosa (about 2 x 5 cm²) in the uppermost part of the nasal cavity, which the sense of smell (this means olfactory ) affect. The secondary ones include the sense of taste (this means gustatory ) relevant receptors on the tongue and palate.