Olfactory epithelium

The olfactory epithelium is a specialized epithellial tissue inside the nasal cavity that is involved in smell. In humans, it measures9 cm2 (3 centimeters by 3 centimeters) and lies on the roof of the nasal cavity about 7 cm above and behind the nostrils. The olfactory epithelium is the part of the olfactory system directly responsible for detecting odors.Composition of the Olfactory receptor neuron (captions in German)olfactory epithelium pig The olfactory epithelium is a specialized epithellial tissue inside the nasal cavity that is involved in smell. In humans, it measures9 cm2 (3 centimeters by 3 centimeters) and lies on the roof of the nasal cavity about 7 cm above and behind the nostrils. The olfactory epithelium is the part of the olfactory system directly responsible for detecting odors. Olfactory epithelium consists of four distinct cell types: The olfactory receptor neurons are sensory neurons of the olfactory epithelium. They are bipolar neurons and their apical poles express odorant receptors on non-motile cilia at the ends of the dendritic knob, which extend out into the airspace to interact with odorants. Odorant receptors bind odorants in the airspace, which are made soluble by the serous secretions from olfactory glands located in the lamina propria of the mucosa. The axons of the olfactory sensory neurons congregate to form the olfactory nerve (CN I). Once the axons pass through the cribriform plate, they terminate and synapse with the dendrites of mitral cells in the glomeruli of the olfactory bulb. Analogous to neural glial cells, the supporting cells are non-neural cells in the olfactory epithelium that are located in the apical layer of the pseudostratified ciliated columnar epithelium. There are two types of supporting cells in the olfactory epithelium: sustentacular cells and microvillar cells. The sustentacular cells function as metabolic and physical support for the olfactory epithelium. Microvillar cells are another class of supporting cells that are morphologically and biochemically distinct from the sustentacular cells, and arise from a basal cell population that expresses c-Kit. Resting on or near the basal lamina of the olfactory epithelium, basal cells are stem cells capable of division and differentiation into either supporting or olfactory cells. While some of these basal cells divide rapidly, a significant proportion remain relatively quiescent and replenish olfactory epithelial cells as needed. This leads to the olfactory epithelium being replaced every 6–8 weeks. Basal cells can be divided on the basis of their cellular and histological features into two populations: the horizontal basal cells, which are slowly dividing reserve cells that express p63; and globose basal cells, which are a heterogeneous population of cells consisting of reserve cells, amplifying progenitor cells, and immediate precursor cells. A brush cell is a microvilli-bearing columnar cell with its basal surface in contact with afferent nerve endings of the trigeminal nerve (CN V) and is specialized for transduction of general sensation. Tubuloalveolar serous secreting glands lying in the lamina propria of the mucosa. These glands deliver a proteinaceous secretion via ducts onto the surface of the mucosa. The role of the secretions are to trap and dissolve odiferous substances for the bipolar neurons. Constant flow from the olfactory glands allows old odors to be constantly washed away. The olfactory epithelium derives from two structures during embryonic development: the olfactory placode, which was long believed to be its sole origin; and neural crest cells, whose contributions have been identified more recently through fate mapping studies.