Olfactory System

olfactory system, the bodily structures that serve the sense of smell. The system consists of the nose and the nasal cavities, which in their upper parts support the olfactory mucous membrane for the perception of smell and in their lower parts act as respiratory passages.

Learn how the olfactory bulb in the brain processes the information from the olfactory receptors lining the noseSee all videos for this article

The bony framework of the nose is part of the skull, but the outer nose is supported only by bone above; lower down, its shape is kept by cartilaginous plates. The expanded lower part of the side of the nose, the ala, is formed only of skin, both externally and internally, with fibrofatty tissue between the layers. The nasal cavities are separated by a septum covered in its lower two-thirds by thick, highly vascular mucous membrane composed of columnar ciliated epithelium with masses of acinous glands embedded in it, while in its upper part it is covered by the less vascular but more specialized olfactory membrane. Near the front of the lower part of the septum a slight opening into a short blind tube, which runs upward and backward, may sometimes be found; this is the vestigial remnant of Jacobson’s organ. The supporting framework of the septum is made up of ethmoid above, vomer below, and the septal cartilage in front. The outer wall of each nasal cavity is divided into three meatuses by the overhanging turbinated bones. Above the superior turbinated bone is a space between it and the roof known as the recessus sphenoethmoidalis, into the back of which the sphenoidal air sinus opens.

See researchers study the mechanism of predictive coding, by which the olfactory system of the brain can anticipate specific smellsSee all videos for this article

Between the superior and middle turbinated bones is the superior meatus, which contains the openings of the posterior ethmoidal air cells, while between the middle and inferior turbinated bones is the middle meatus, which is the largest of the three and contains a rounded elevation, the bulla ethmoidalis. Above and behind this is often an opening for the middle ethmoidal cells; below and in front runs a deep sickle-shaped gutter, the hiatus semilunaris, which communicates above with the frontal air sinus and below with the opening into the antrum of Highmore or maxillary antrum. The inferior meatus is below the inferior turbinated bone, and, when that is lifted, the valvular opening of the nasal duct is seen. The roof of the nose is narrow, and it is here that the olfactory nerves pass in through the cribriform plate. The floor is wider so that a coronal section through each nasal cavity has roughly the appearance of a right-angled triangle.