The olfactory mucosa is a specialized patch of tissue responsible for our sense of smell. This small area of cells plays a large part in detecting odors that circulate in the air. The detection of these odors influences a wide range of perceptions and behaviors, from how we experience the flavor of food to our ability to identify potential hazards like smoke or spoiled food.
Location and Composition of the Olfactory Mucosa
The olfactory mucosa is located in a small region on the roof of the nasal cavity, covering the superior nasal conchae. Roughly the size of a postage stamp, this area is anatomically distinct from the rest of the nasal passages. The tissue itself is a specialized form of pseudostratified columnar epithelium, specifically known as the olfactory epithelium, which lies on top of a layer of connective tissue called the lamina propria.
Within the olfactory epithelium, there are three main types of cells. The most important are the olfactory receptor neurons, which are bipolar nerve cells that directly sense odor molecules. These neurons are supported by sustentacular cells, which provide both physical structure and metabolic maintenance, similar to glial cells in the nervous system.
The third cell type is the basal cell, which acts as a stem cell for the tissue. These cells are responsible for regenerating both the olfactory neurons and the supporting cells throughout a person’s life. This regenerative capacity is a unique feature, allowing the sense of smell to recover after certain types of damage or infection.
The Mechanism of Smell
The process of smelling begins when airborne molecules are inhaled into the nasal cavity. A thin layer of mucus, secreted by Bowman’s glands located in the lamina propria, covers the entire olfactory epithelium. This mucus layer is not just a protective barrier; its primary role is to dissolve the inhaled odorant molecules, preparing them for detection.
Once dissolved in the mucus, the odor molecules bind to specific protein receptors located on the cilia, which are tiny, hair-like projections extending from the dendrites of the olfactory receptor neurons. Each neuron typically expresses one type of receptor, which is specialized to recognize a particular chemical feature of an odorant.
The binding of an odorant to its receptor triggers a change within the neuron, generating a small electrical signal. This signal travels down the neuron’s axon, a long fiber that extends from the cell body. These axons bundle together to form the olfactory nerve, which passes through small openings in the cribriform plate, a bone at the base of the skull. The signal is then transmitted directly to the olfactory bulb in the brain, where it is processed and interpreted as a specific smell.
Distinguishing Olfactory from Respiratory Mucosa
While the olfactory mucosa is dedicated to smell, most of the nasal cavity is lined with a different tissue called respiratory mucosa. The primary function of the respiratory mucosa is to warm, humidify, and filter the air we breathe before it reaches the lungs. The respiratory tissue achieves its filtering function through the coordinated action of cilia and mucus-producing goblet cells.
The two types of mucosa also have a different appearance. The olfactory mucosa is typically yellowish-brown in color due to the presence of specific pigments within the supporting cells. In contrast, the respiratory mucosa is pinkish because it has a much richer supply of blood vessels close to the surface.
At a microscopic level, their cellular makeup is distinct. The olfactory epithelium contains the specialized olfactory receptor neurons for detecting odors. The respiratory epithelium, however, lacks these neurons and is instead populated with ciliated cells that sweep mucus towards the throat and goblet cells that produce that mucus.