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Department of Molecular Physiology

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olfaction
Histology

The nasal cavity of mammals houses an intricate system of turbinates which serve to warm, to moisten, and to analyze the inhaled air. The posterior sections of these structures are covered with chemosensory tissue, the olfactory neuroepithelium. Olfactory sensory neurons in this epithelium detect the presence of odorants and generate neuronal signals that inform the brain about the chemical composition of the air. A cross (coronal) section of the nose shows the nasal septum in the middle and to its right and left three turbinates which have a mushroom-like shape in the cross section. (Richardson stain)

The olfactory sensory neurons of each nasal cavity project their axons to one of the two olfactory bulbs. Axons from about 1000 sensory neurons of the same odor specificity converge onto a single brain cell: a mitral cell in the olfactory bulb. The synapses between these equally tuned sensory neurons and a mitral cell form within a small, globular plexus - a glomerulum. Roughly 2500 such glomeruli receive convergent input from the olfactory epithelium. They constitute the outermost layer of the bulb and can be seen in this cross section of posterior region of the nose where the bulb is located above the nasal cavity. Axons of the neurons which are located in the olfactory epithelium reach the bulb through pores in the cribriform plate, the bone plate that separates the nasal cavity from the brain (Masson-Goldner stain).

The olfactory neuroepithelium grows on a support of bone (blue) which forms the structural basis of the turbinates. The submucosal tissue (light blue, grey) containes mainly nerve bundles, blood vessels, and connective tissue. The apical surface is formed by a single layer of epithelial cells (supporting cells, red/brown). Between submucosa and supporting cells, several layers of olfactory sensory neurons (red) can be seen. They send a single dendrite to the apical surface which terminates in a tuft of cilia, the chemosensory membrane of olfactory sensory neurons (Azan stain).



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