Olfactory epitheliumIt holds the receptor neurons that detect smells.
Olfactory receptor neuronsEach has a dendrite down to the surface. Its axon goes up toward the brain.
Supporting cellsThey support and protect the receptor neurons.
CiliaOdorant molecules dissolve in the mucus and bind to receptors on them.
MucusSmells must dissolve in it before they can be detected.
The path to the brain 4
Olfactory nerveThe axons of the receptor neurons; together they are cranial nerve I.
Cribriform platePart of the ethmoid bone. The nerve fibres pass up through its holes.
Olfactory bulbIt lies on the cribriform plate. It passes the signal on to the brain.
Olfactory tractIt carries the smell signal on to the brain.
How this list was compiled: Every name and detail checked on 2026-09-29 against OpenStax Anatomy and Physiology 2e, section 14.1 Sensory Perception (olfactory epithelium, olfactory receptor neurons with dendrites, cilia and axons, supporting cells, mucus and odorant molecules, the olfactory nerve through the cribriform plate of the ethmoid bone to the olfactory bulb and tract), https://openstax.org/books/anatomy-and-physiology-2e/pages/14-1-sensory-perception, and against Wikipedia, Olfactory system and Olfactory epithelium, text only. Licence: own work
The drawing: Drawn for this site on 2026-10-05 by script. The head section is composed after Gray's Anatomy (1918) fig. 855, Lateral wall of nasal cavity (https://commons.wikimedia.org/wiki/File:Gray855.png), by Henry Vandyke Carter, public domain, with the brain, olfactory bulb, tract and epithelium added; the enlarged pathway is laid out after the plan of olfactory neurons, fig. 772 of the same book (https://commons.wikimedia.org/wiki/File:Gray772.png), public domain. The outline of the head section is plotted point by point after the first plate. Licence: own work
How it works
Smell starts in a small patch of lining in the roof of the nose. The first drawing enlarges that patch and the path above it; the second shows where it sits, under the base of the skull.
Read the full guide
From the air up to the brain
Numbers 1 to 5 are in the lining: the epithelium, its receptor neurons and supporting cells, the cilia and the mucus they reach into. Numbers 6 to 9 are the path up: the nerve fibres, the cribriform plate they pass through, the olfactory bulb and the tract.
A smell has to dissolve in the mucus first; only then can the cilia detect it.
Questions and answers
How does the sense of smell work?
Odorant molecules in the air dissolve in the mucus in the roof of the nose and bind to receptors on the cilia of olfactory receptor neurons. Their axons carry the signal through the cribriform plate to the olfactory bulb and on along the olfactory tract.
What is the cribriform plate?
A thin plate of the ethmoid bone in the roof of the nasal cavity, full of small holes. The olfactory nerve fibres pass up through the holes to the olfactory bulb.
What is the olfactory nerve?
Cranial nerve I: the bundles of axons of the olfactory receptor neurons, running from the olfactory epithelium through the cribriform plate to the olfactory bulb.