ABSTRACT
A sense of smell in humans is important in feeding and probably also in sexual behavior. Olfactory epithelium lies in the dorsal nasal cavity. Odor molecules are usually small, lipid soluble and volatile. Initially they bind to odor-binding proteins in the mucus which probably act to concentrate the odor molecules in the vicinity of the cilia. Each olfactory receptor neuron (ORN) probably expresses just a single subtype of odorant receptor. Because odorant receptors are relatively nonspecific, individual ORNs respond to a number of odors, collectively referred to as the molecular receptive range. A dendrite emerges from one pole of the ORN and extends to the surface of the epithelium, forming a knob which gives rise to a cluster of six to 12 immobile olfactory cilia which lie within a mucus layer which is secreted by the supporting cells.
