Human nasal respiratory mucosa has a limited capacity for localization of stimuli and discrimination of sensory modalities. In order to obtain morphological data on its receptor organs, histochmeical and electron microscopical studies were undertaken in six individuals ranging in age from 18 to 39 years.

It was found that the nasal respiratory mucosa was supplied by non-myelinated nerves which approached the mucosa in fascicles containing up to 200 axons. These fascicles were devoid of perineurial sheaths. They ramified repeatedly producing only one type of receptor organ — a simple terminal arborization. The finest terminal fascicles of the plexus ended either in the cell free zone of the lamina propria or in the spaces between the epithelial cells next to the basement membrane. The axons in the fascicles and in the endings were only partly insulated from one another by Schwann cell folds. The axoplasm of the terminal and preterminal nerve fibers contained accumulations of fine vesicles, simple granules and clusters of mitochondria. All nerve fibers gave a positive acetyl- and a negative butyro-cholinesterase reaction.

The plexiform endings of the nasal respiratory mucosa are different from any receptor organ of the adult human skin. They are reminiscent of the transitory, yet functional plexiform endings of the fetal skin which are found prior to the formation of the definitive receptor organs.