Recently, there are always patients consulting with me about olfactory problems, which cannot be clearly explained in one or two sentences, so I wrote this small scientific article, hoping to help those who are interested.
During the embryonic stage, the first mucous membrane that appears in the nasal cavity is the olfactory mucosa. However, because the human brain is more developed than other mammals, the sense of smell becomes less important, so the olfactory mucosa also gradually degenerates, leaving only a small part – the upper part of the nasal cavity, the middle turbinate and the upper 1/3 of the nasal septum, about a few square centimeters.
So how does the sense of smell come about? Firstly, volatile substances enter the nasal cavity and touch the mucous membrane of the olfactory area. This process is both chemical and neurological, so it is said that the olfactory process is fine and highly sensitive. In this small piece of mucosa of a few square centimeters, scientists have found that it can distinguish 2000-4000 different odors. These odors can be simply categorized into four basic odors: fragrant, sour, burnt and pungent.
There are many factors that affect the sense of smell, such as humidity and temperature, which can change the sensitivity of smell, long time smell of a certain smell, which can produce olfactory adaptations, mental factors, gender and age, which can affect the sense of smell, and before and after meals, which also have great differences.
So what is the role of smell in the end? What are the harmful effects of no sense of smell?
The sense of smell is like a sophisticated chemical analyzer, which mainly works in two aspects.
One, is to find food: it is an animal’s instinct, especially when hungry.
Two, it is the protective role of smell: when smelling some harmful and irritating odor, it reports to the brain, which sends a command to stop breathing and stay away from harmful substances. The sense of smell is like our body’s faithful scout, but his working environment needs moist conditions and unobstructed air.
Any factor that clogs the nasal cavity will affect their work and thus reduce their usefulness. For example, when the nose is blocked, the olfactory mucosa and the olfactory nerve cannot come in contact with the odor particles, so of course they cannot smell, and doctors call this phenomenon as blocked hyposmia. It is common in nasal deformity (collapsed nose, anterior and posterior nasal atresia, deviated nasal septum), rhinitis, sinusitis, nasal polyps, nasal trauma (resulting in nasal narrowing), nasal foreign body, tumor, etc. In addition, when the nasal cavity is dry, it destroys the moist environment and, of course, reduces its sensitivity, for example, odorous nasal syndrome.
During the work of olfactory nerve, it often suffers from the poisoning of some factors. For example, when you have a cold, it is often accompanied by reduced sense of smell, but some people recover from the cold and the sense of smell is not restored, this is the process of cold and the olfactory nerve is attacked by virus, so virus is a common killer. There are also some drugs, such as nasal drops of long-term astringent drugs such as carbonic acid, nitric acid, zinc, anesthetics, formaldehyde, and streptomycin, gentamicin, etc., which can also poison the olfactory nerve. Long-term heavy smoking is also toxic to the olfactory nerve.
The olfactory process is controlled by the olfactory nerve center of the brain. Some diseases can make the olfactory center of the brain lose its ability to command, and this loss of olfactory function is called central olfactory loss. These include traumatic brain injury, meningitis, brain abscess, brain tumor, etc.
There are also some other olfactory abnormalities, including abnormal sensitivity of olfactory function, olfactory inversion, phantom smell, wrong smell, etc. These belong to the range of neurological disorders. Common causes include: hysteria, epilepsy, neurasthenia, schizophrenia and women’s menstruation, pregnancy, puerperium and menopause, etc. All of them can have abnormal smell.