The olfactory mucosa is responsible for the sense of smell. It is located as part of the nasal mucosa in the area of the roof of the nose. Diseases of the olfactory mucosa can lead to olfactory disorders.
What is the olfactory mucosa?
The olfactory mucosa contains special sensory cells that pick up odors and transmit the information via electrical impulses to the brain for processing. Within the olfactory cells, so-called chemoreceptors ensure the absorption of odor molecules. In humans, olfactory cells are located in the regio olfactoria of the nasal mucosa. The regio olfactoria refers to the part of the nasal mucosa responsible for the perception of odors. It is located on the left and right sides in the roof of the upper nasal cavity. In this area, in addition to the olfactory cells, there are supporting and basal cells. The olfactory cells are so-called bipolar neurons with dendrites and axons as nerve processes. Dendrites provide the input of electrical impulses, while axons transmit these impulses. The sensory cells renew themselves every 60 days. Thus, olfactory cells are among the few nerve cells that are constantly renewed. They develop from basal cells, which are the stem cells of the nasal mucosa. The supporting cells stabilize the tissue structure of the olfactory mucosa.
Anatomy and structure
The olfactory mucosa, located in the roof of the upper nasal mucosa, is brown in color and occupies an approximate area of 2 x 5 cm. It is composed of olfactory cells, supporting cells, microvilli cells, and basal cells. It also contains serous glands. Humans have approximately 10 – 30 million olfactory sensory cells. In comparison, their number in dogs is about 250 million. Each olfactory cell still carries 5 – 20 hairs with olfactory receptors. These hairs protrude from the mucous membrane and are covered with a thin layer of mucus. Odor molecules arriving there dock onto the odor receptors and set them in excitation. There are approximately 350 different types of olfactory receptors. Each type responds to only one specific molecule. So 350 different odors can be distinguished. But the processing and filtering of these impressions is accomplished by the bundled outgoing nerve fibers, the axons. These axon bundles are connected to an upstream part of the brain, the olfactory bulb. This is where the synaptic circuitry of the sense of smell takes place. From there, the information is passed on to the corresponding brain centers. At the olfactory bulb, the axon strands are divided into two parts. The medial strand reaches the olfactory tubercle. There, the information is stored but remains unconscious. The lateral strand leads to the primary olfactory cortex, where information from the olfactory mucosa is consciously processed.
Function and tasks
By performing its function, the olfactory mucosa contributes significantly to the health of the body. This is because the olfactory function protects the organism and especially the respiratory organs from the harmful effects of toxic substances. Foul-smelling gases create a feeling of disgust, so that the corresponding organism moves away from the danger zone as quickly as possible. On the other hand, pleasant odors attract people because they are usually associated with positive things, such as delicious food. However, the sense of smell is often not taken very seriously. However, people who no longer have a sense of smell can find themselves in dangerous situations without being noticed. For example, it is no longer possible for these patients to detect spoiled food or escaping gas by smell alone. Therefore, during evolution, the corresponding olfactory receptors have also evolved for vital odors. Odorant receptors are certain proteins that are still coupled to a G protein. According to the lock-and-key principle, they have developed precisely fitting forms with respect to certain odor molecules. The signal molecule is conducted to the receptor via a hairs of the olfactory cell, where it combines with the receptor if there is an exact match. The resulting excitation is then transmitted via the axons. So-called mitral cells in the olfactory bulb then probe and amplify identical odors among the selection of 350 different receptors and forward them to the corresponding brain centers. There, the excitations evoked by certain signal molecules in the receptor molecules of the olfactory cells are made conscious by olfactory impressions.
Diseases
Diseases of the nasal mucosa and specifically the olfactory mucosa can lead to olfactory disorders. Olfactory disorder is the collective term of a variety of deviant olfactory sensations. First of all, a distinction must be made between quantitative and qualitative olfactory disorders. Quantitative olfactory disorders indicate a partial (hyposmia) or complete loss (anosmia) of the ability to smell. Hypersensitivity to olfactory stimuli (hyperosmia) also occurs. Causes of anosmia or hyperosmia can be brain diseases, viral infections, chronic inflammation of the nasal mucosa, allergies or side effects of medications. Since the sense of smell is closely connected to the sense of taste, the taste of food can also no longer be perceived correctly. This often leads to malnutrition. In addition, especially for older people, there is a risk of food poisoning from spoiled food. Psychological problems, such as depression, can also result from the absence of the sense of smell. Qualitative olfactory disorders manifest themselves in deviant olfactory sensations. Thus, in parosmia, there is an altered perception of odors. Phantosmia leads to the perception of odors that do not exist. It can be considered an odor-related hallucination. In cacosmia, pleasant odors are perceived as unpleasant, while in euosmia, unpleasant odors appear pleasant. Qualitative olfactory disorders can be caused by damage to the olfactory mucosa, among many other causes.
Typical and common nasal disorders
- Stuffy nose
- Nasal polyps
- Sinusitis
