Organ of Smell

Q: Into what structures does the olfactory tract divide in the region of the olfactory trigone?

In the region of the olfactory trigone (trigonum olfactorium), the olfactory tract divides into olfactory striae (striae olfactoriae). These include: Medial olfactory stria — its fibers cross over to the contralateral side.Lateral olfactory stria — courses toward the amygdala, semilunar, and ambient gyri. These structures conduct impulses to the cortical olfactory centers.

Organum olfactus

For medical students2 min readUpdated 2026-10-10

The organ of smell (organum olfactus) is the peripheral part of the olfactory system. It is localized in a specific region of the nasal cavity and is responsible for the primary reception of odorant molecules and their subsequent transformation into a nerve impulse.

LocationSuperior nasal meatus and upper parts of the nasal septum

Mucosa ColorYellowish-brown color, distinct from the respiratory mucosa

Bowman GlandsSecrete serous fluid to dissolve odorant molecules

Neural PathwayProjects directly to the cerebral cortex without thalamic relay

Olfactory Region of the Mucous Membrane

A specialized zone in the nasal cavity is termed the olfactory region of the nasal mucosa (regio olfactoria tunicae mucosae nasi). It occupies the superior nasal meatus and the upper parts of the nasal septum.

This region has several striking differences from the rest of the respiratory nasal mucosa:

Thickness: The olfactory mucosa is significantly thicker.
Color: It has a characteristic yellowish-brown color.
Epithelium: Typical respiratory ciliated epithelium is completely absent.
Glands: It contains specific olfactory glands (glandulae olfactoriae, or Bowman glands). Their main function is the secretion of serous fluid necessary to dissolve odorants (molecules can only interact with receptors when in a dissolved state).

Structure of the Olfactory Epithelium

The surface of the olfactory region is lined by a specialized pseudostratified olfactory epithelium (epithelium olfactorium). It contains three key cell types, each performing a unique task:

Olfactory neurosensory cells (cellulae neurosensoriales olfactoriae). These are bipolar neurons that act as the true receptors. Their apical poles form olfactory vesicles with cilia that capture odor molecules. Their basal poles give rise to axons that form nerve fibers.
Supporting cells (cellulae sustentaculares). These perform structural and trophic (nutritional) functions. Additionally, they play a crucial role in the detoxification of odorants, protecting receptors from damage.
Basal cells (cellulae basales). Located at the base of the epithelium, they serve as a stem cell reserve for the regeneration of the olfactory epithelium, ensuring the continuous renewal of neurosensory cells.

Olfactory Nerves and Pathway

The central (basal) processes of the olfactory neurosensory cells do not travel alone; they bundle together to form the olfactory nerves (nn. olfactorii).

The subsequent pathway of the impulse is as follows:

Nerve fiber bundles enter the cranial cavity through the foramina of the cribriform plate of the ethmoid bone (lamina cribrosa ossis ethmoidalis).
The fibers terminate in the olfactory bulb (bulbus olfactorius), where the first synaptic transmission occurs.
From the bulb, the impulse travels via the olfactory tract (tractus olfactorius) directly to the primary olfactory centers in the cerebral cortex.

A critical feature of the olfactory system: the nerve impulse reaches the cerebral cortex without synapsing in the thalamus (unlike most other sensory systems).

Mnemonic

To remember the epithelial cells: "Neurons, Support, and Base." Neurosensorial = catch scents; Supporting = nourish and clear; Basal = generate new cells.

Frequently asked questions

Which structures of the cerebral cortex serve as the primary olfactory centers?

The primary cortical olfactory centers are located within the temporal lobes. These include:

Uncus — the cortical olfactory area where the fibers of the olfactory pathway terminate.
Parahippocampal gyrus (gyrus parahippocampalis) — includes the anterior part (Brodmann area 28).

Subjective perception of odors arises within these gyri.

With which cells do the olfactory nerve fibers synapse in the olfactory bulb?

Olfactory nerve fibers synapse with the dendrites of several cell types within the olfactory bulb. Excitation is transmitted to:

Mitral cells — second-order neurons that converge inputs from numerous fibers.
Tufted cells — participate in forming the olfactory pathway.
Granule cells — receive signals via complex synapses.

Axon terminals form olfactory glomeruli (glomeruli olfactorii) within the bulb.

Into what structures does the olfactory tract divide in the region of the olfactory trigone?

In the region of the olfactory trigone (trigonum olfactorium), the olfactory tract divides into olfactory striae (striae olfactoriae). These include:

Medial olfactory stria — its fibers cross over to the contralateral side.
Lateral olfactory stria — courses toward the amygdala, semilunar, and ambient gyri.

These structures conduct impulses to the cortical olfactory centers.

How does the olfactory mucosa differ from the respiratory mucosa?

It is thicker, has a yellowish-brown color, and lacks classical ciliated respiratory epithelium.

What is the function of Bowman glands?

They produce a fluid serous secretion that dissolves odorant molecules. Without dissolution, odor molecules cannot bind to neurosensory cell receptors.

Does the olfactory impulse pass through the thalamus?

No. This is a unique feature of the system: from the olfactory bulb via the olfactory tract, the impulse goes straight to the primary cortical centers, bypassing the thalamus.

Go deeper

Mechanism of odorant detoxification by supporting cells
Histophysiology of olfactory vesicles and receptor cilia
Topographical anatomy of the lamina cribrosa and nerve passage
Process and timeline of neurosensory cell regeneration from basal cells
Localization of primary olfactory centers in the cerebral cortex