Surface morphology of olfactory receptors.

The receptor cells of the olfactory system have cilia on their apical terminals. The receptor cells of the vomeronasal system lack cilia on their distal terminals, having microvilli in their place. Since both these systems have the capacity to detect airborne stimuli, it is apparent that ciliary structure per se is not necessary for the chemoreceptive function and that cilia on olfactory receptor cells may then serve a mechanical or structural role for supporting specialized chemosensitive membrane. The spread of conductance changes across this chemosensitive membrane to proximal spike generating regions requires electrotonic cytoplasmic continuity from the ciliary shaft to the axon hillock. We have demonstrated this continuity by showing that intra-axonally injected HRP can spread from the axon to the cell soma and from there to the interior of the ciliary shafts.