The sense of smell is one of the first sensations that appear in an infant. From it begins the knowledge of the world and himself. The taste that a person feels while eating is also a merit of smell, and not of language, as it seemed before. Even the classics claimed that our scent is able to help in a difficult situation. As J.R. R. Tolkien wrote: "If you get lost, always go where it smells better."
Anatomy
The olfactory nerve belongs to the group of cranial, as well as nerves of special sensitivity. It takes its beginning on the mucosa of the upper and middle nasal passage. The processes of sensor cells form there the first neuron of the olfactory tract.
Fifteen to twenty bezmyelinovy fibers penetrate into the cranial cavity through a horizontal plate of the ethmoid bone. There they merge into the olfactory bulb, which is the second neuron of the path. Long nerve processes emerge from the bulb, which are directed to the olfactory triangle. Then they are divided into two parts and immersed in the front perforated plate and a transparent partition. There are third neurons of the path.
After the third neuron, the tract goes to the cerebral cortex, namely to the hook region, to the olfactory analyzer. At this site, the olfactory nerve ends. Its anatomy is quite simple, which allows doctors to identify violations in different areas and eliminate them.
Functions
The name of the structure itself indicates what it is intended for. The functions of the olfactory nerve are to capture the smell and its interpretation. They cause appetite and salivation if the aroma is pleasant, or, on the contrary, provoke nausea and vomiting, when the amber leaves much to be desired.
In order to achieve this effect, the olfactory nerve passes through the reticular formation and is sent to the brain stem. There, the fibers connect to the nuclei of the intermediate, glossopharyngeal and vagus nerves. The nucleus of the olfactory nerve is also located in this area.
The fact is known that certain smells evoke certain emotions in us. So, to provide such a reaction, the olfactory nerve fibers bind to the subcortical visual analyzer, hypothalamus and limbic system.
Anosmia
"Anosmia" translates as "lack of smell." If a similar condition is observed from two sides, then this indicates the defeat of the nasal mucosa (rhinitis, sinusitis, polyps) and, as a rule, does not face any serious consequences. But with a unilateral loss of smell, you need to think about the fact that the olfactory nerve can be affected.
The causes of the disease can be an underdeveloped olfactory tract or fractures of the bones of the skull, for example, the ethmoid plate. The course of the olfactory nerve is generally closely related to the bone structures of the skull. Fragments of the bone can also damage the bone fragments after a fracture of the nose, upper jaw, orbit. Damage to the olfactory bulbs is also possible due to contusion of the substance of the brain, when falling on the back of the head.
Inflammatory diseases, such as ethmoiditis, in advanced cases melt the ethmoid bone and damage the olfactory nerve.
Hyposmia and hyperosmia
Hyposmia is a decrease in smell. It can arise due to the same reasons as anosmia:
- thickening of the nasal mucosa;
- inflammatory diseases;
- neoplasms;
- injuries.
Sometimes this is the only sign of cerebral aneurysm or tumor of the anterior cranial fossa.
Hyperosmia (increased or exacerbated sense of smell) is noted in emotionally labile people, as well as in some forms of hysteria. Hypersensitivity to odors is observed in people who inhale drugs, such as cocaine. Sometimes hyperosmia is due to the fact that the innervation of the olfactory nerve extends to a large area of the nasal mucosa. Such people, most often, become workers in the perfume industry.
Parosmia: olfactory hallucinations
Parosmia is a perverse odor perception that normally occurs during pregnancy. Pathological parosmia is sometimes observed with schizophrenia, damage to the subcortical centers of smell (para-hippocampal gyrus and hook), with hysteria. In patients with iron deficiency anemia, similar symptoms are observed: pleasure from the smell of gasoline, paint, wet asphalt, chalk.
Lesions of the olfactory nerve in the temporal lobe cause a specific aura before epileptic seizures and cause hallucinations in psychoses.
Research Methodology
In order to determine the state of smell in a patient, a neuropathologist conducts special tests to recognize various odors. Indicator flavors should not be too harsh so as not to interfere with the purity of the experiment. The patient is asked to calm down, close his eyes and press his nostril with his finger. After that, a smelling substance is gradually brought to the second nostril. It is recommended to use odors familiar to humans, but at the same time to avoid ammonia, vinegar, since when inhaled, in addition to the olfactory, the trigeminal nerve is also irritated.
The doctor records the test results and interprets them relative to the norm. Even if the patient cannot name the substance, the mere fact of smelling eliminates nerve damage.
Brain Tumors and Smell
With brain tumors of various locations, hematomas, impaired cerebrospinal fluid outflow, and other processes that compress the brain substance or press it to the bone formations of the skull. In this case, a one- or two-sided violation of the sense of smell may develop. The doctor should remember that the nerve fibers intersect, therefore, even with the localization of the lesion on the one hand, the hyposmia will be bilateral.
The defeat of the olfactory nerve is an integral part of the craniobasal syndrome. It is characterized not only by compression of the brain substance, but also by its ischemia. Patients develop pathology of the first six pairs of cranial nerves. Symptoms may be uneven, there are various combinations.
Treatment
Pathologies of the olfactory nerve in its first section are most often found in the autumn-winter period, when there is a massive incidence of acute respiratory infections and influenza. A prolonged course of the disease can cause a complete loss of smell. Recovery of nerve functions takes from ten months to a year. All this time, it is necessary to carry out course treatment to stimulate regenerative processes.
In the acute period, ENT prescribes physiotherapeutic treatment:
- microwave therapy of the nose and maxillary sinuses;
- ultraviolet irradiation of the nasal mucosa, with a capacity of 2-3 biodoses;
- magnetotherapy of the wings of the nose and sinuses of the upper jaw;
- infrared radiation with a frequency of 50-80 Hz.
You can combine the first two methods and the last two. This speeds up the restoration of lost functions. After clinical recovery, the following physiotherapeutic treatment is also carried out for rehabilitation:
- electrophoresis using drugs "No-spa", "Proserin", as well as nicotinic acid or lidase;
- phonophoresis of the nose and maxillary sinuses for ten minutes daily;
- red laser irradiation;
- endonasal electrical stimulation.
Each course of therapy is carried out for up to ten days with intervals of fifteen to twenty days until the olfactory nerve function is fully restored.