Olfactory epithelium
Encyclopedia
The olfactory epithelium is a specialized epithelial
tissue inside the nasal cavity
that is involved in smell
. In humans, it measures about 1 square centimetre (on each side) 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 odor
s.
(cranial nerve I). The apical poles of these neurons are covered with non-motile cilia, with the plasma membrane containing odorant-binding proteins acting as olfactory receptor
s. The incoming odorants are made soluble by the serous secretion from Bowman's Glands, located in the lamina propria
of the mucosa.
s) of the olfactory epithelium function as metabolic and physical support for the olfactory cells. Histologically, the supporting cells are tall columnar cells featuring microvilli and a prominent terminal web
. The nuclei of supporting cells are more apically located than those of the other olfactory epithelial cells.
Basal cells can be divided on the basis of cellular anatomy histological markers into two populations: the horizontal basal cells which line the olfactory epithelium and the slightly more superficial globose basal cells. Horizontal basal cells are now thought to be the primary stem cell population supplying new cells in this system., although this is subject to some debate with some scientists maintaining that the globose basal cells are the true stem cells.
(cranial nerve V), rather than the olfactory nerve, as afferent olfactory signals are.
.
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
tissue inside the nasal cavity
Nasal cavity
The nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...
that is involved in smell
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...
. In humans, it measures about 1 square centimetre (on each side) 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
Olfactory system
The olfactory system is the sensory system used for olfaction, or the sense of smell. Most mammals and reptiles have two distinct parts to their olfactory system: a main olfactory system and an accessory olfactory system. The main olfactory system detects volatile, airborne substances, while the...
directly responsible for detecting odor
Odor
An odor or odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors...
s.
Layers of olfactory epithelium
Olfactory epithelium consists of four distinct cell types:- Olfactory cells
- Supporting cells
- Basal cells
- Brush Cells
Olfactory cells
The olfactory cells of the epithelium are bipolar neurons which congregate to form the olfactory nerveOlfactory nerve
The olfactory nerve, or cranial nerve I, is the first of twelve cranial nerves. It is instrumental in the sense of smell. Derived from the embryonic nasal placode, the olfactory nerve is capable of regeneration.-Anatomy:...
(cranial nerve I). The apical poles of these neurons are covered with non-motile cilia, with the plasma membrane containing odorant-binding proteins acting as olfactory receptor
Olfactory receptor
Olfactory receptors expressed in the cell membranes of olfactory receptor neurons are responsible for the detection of odor molecules. Activated olfactory receptors are the initial player in a signal transduction cascade which ultimately produces a nerve impulse which is transmitted to the brain...
s. The incoming odorants are made soluble by the serous secretion from Bowman's Glands, located in the lamina propria
Lamina propria
The lamina propria is a constituent of the moist linings known as mucous membranes or mucosa, which line various tubes in the body ....
of the mucosa.
Supporting cells
Analogous to neural glial cells, the supporting cells (a.k.a. Sustentacular cellSustentacular cell
A sustentacular cell is a type of cell primarily associated with structural support.One type of sustentacular cell is the Sertoli cell, in the testicle...
s) of the olfactory epithelium function as metabolic and physical support for the olfactory cells. Histologically, the supporting cells are tall columnar cells featuring microvilli and a prominent terminal web
Terminal web
The terminal web is a filamentous structure found at the apical surface of epithelial cells that possess microvilli. It is composed primarily of filaments of actin filaments stabilized by spectrin, which also anchors the terminal web to the apical cell membrane. The presence of myosin II and...
. The nuclei of supporting cells are more apically located than those of the other olfactory epithelial cells.
Basal cells
Resting on the basal lamina of the olfactory epithelium, basal cells are stem cells capable of division and differentiation into either supporting or olfactory cells. The constant divisions of the basal cells leads to the olfactory epithelium being replaced every 2–4 weeks.Basal cells can be divided on the basis of cellular anatomy histological markers into two populations: the horizontal basal cells which line the olfactory epithelium and the slightly more superficial globose basal cells. Horizontal basal cells are now thought to be the primary stem cell population supplying new cells in this system., although this is subject to some debate with some scientists maintaining that the globose basal cells are the true stem cells.
Brush Cells
A microvilli-bearing columnar cell with basal surface in contact with afferent nerve endings, specialised for transduction of general sensation. Nerve fibres are terminal branches of trigeminal nerveTrigeminal nerve
The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...
(cranial nerve V), rather than the olfactory nerve, as afferent olfactory signals are.
Bowman's (Olfactory) Glands
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 Bowman's glands allows old odors to be constantly washed away.Pathology
The olfactory epithelium can be damaged by inhalation of toxic fumes, physical injury to the interior of the nose, and possibly by the use of some nasal sprays. Because of its regenerative capacity, damage to the olfactory epithelium can be temporary but in extreme cases, injury can be permanent, leading to anosmiaAnosmia
Anosmia is a lack of functioning olfaction, or in other words, an inability to perceive odors. Anosmia may be either temporary or permanent. A related term, hyposmia, refers to a decreased ability to smell, while hyperosmia refers to an increased ability to smell. Some people may be anosmic for one...
.