Smell is one of the first sensations that a baby has. It begins with the knowledge of the world around and oneself. The taste that a person feels while eating is also a merit of smell, and not of the tongue, as it seemed before. Even the classics claimed that our sense of smell is able to help in a difficult situation. As J. R. R. Tolkien wrote: “When you are lost, always go where it smells best.”
Anatomy
The olfactory nerve belongs to the group of cranial, as well as nerves of special sensitivity. It originates on the mucous membrane of the upper and middle nasal passages. The processes of neurosensory cells form the first neuron of the olfactory tract there.
Fifteen to twenty unmyelinated fibers enter the cranial cavity through the horizontal plate of the ethmoid bone. There they combine to form the olfactory bulb, which is the second neuron of the pathway. Long nerve processes emerge from the bulb, which go to the olfactory triangle. Then they are divided into two parts and immersed in the anterior perforated plate and transparent septum. There are the third neurons of the path.
After the third neuron, the tract goes to the cortexlarge brain, namely to the area of the hook, to the olfactory analyzer. The olfactory nerve ends at this site. Its anatomy is quite simple, which allows doctors to identify violations in different areas and eliminate them.
Functions
The very name of the structure indicates what it is intended for. The functions of the olfactory nerve are to capture the smell and decipher it. 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.
To achieve this effect, the olfactory nerve passes through the reticular formation and travels to the brainstem. There, the fibers connect with the nuclei of the intermediate, glossopharyngeal and vagus nerves. The olfactory nerve nuclei are also located in this area.
It is known that certain smells evoke certain emotions in us. So, to provide such a reaction, the fibers of the olfactory nerve communicate with the subcortical visual analyzer, the hypothalamus and the limbic system.
Anosmia
"Anosmia" translates as "lack of smell". If such a condition is observed on both sides, then this testifies in favor of damage to the nasal mucosa (rhinitis, sinusitis, polyps) and, as a rule, does not threaten any serious consequences. But with a one-sided loss of smell, you need to think about the fact that the olfactory nerve may be affected.
Causesdiseases may be an underdeveloped olfactory tract or fractures of the bones of the skull, for example, the cribriform plate. The course of the olfactory nerve is generally closely related to the bone structures of the skull. Fragments of bone after a fracture of the nose, upper jaw, and orbit can also damage the fibers. Damage to the olfactory bulbs is also possible due to bruising 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 the sense of smell. It can occur due to the same reasons as anosmia:
- thickening of the nasal mucosa;
- inflammatory diseases;
- neoplasms;
- injury.
Sometimes this is the only sign of a cerebral aneurysm or anterior fossa tumor.
Hyperosmia (increased or heightened sense of smell), observed in emotionally labile people, as well as in some forms of hysteria. Hypersensitivity to odors is seen 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 employees of the perfume industry.
Parosmia: olfactory hallucinations
Parosmia is a perverse sense of smell that normally occurs during pregnancy. Pathologicalparosmia is sometimes observed in schizophrenia, damage to the subcortical centers of smell (parahippocampal gyrus and hook), and hysteria. Patients with iron deficiency anemia have similar symptoms: pleasure from the smell of gasoline, paint, wet asph alt, 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 the patient's sense of smell, a neuropathologist conducts special tests to recognize various odors. Indicator aromas should not be too harsh, so as not to disturb 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 avoid ammonia, vinegar, since when they are 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 very fact of smelling it rules out nerve damage.
Brain tumors and sense of smell
With brain tumors of various localization, hematomas, impaired outflow of cerebrospinal fluid and other processes that compress the substance of the brain or press it against the bone formations of the skull. In this case, one- or two-sided violation of the sense of smell may develop. The physician should remember thatnerve fibers cross, so even if the lesion is localized on one side, 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 medulla, but also by its ischemia. Patients develop pathology of the first six pairs of cranial nerves. Symptoms may be uneven and various combinations occur.
Treatment
Pathologies of the olfactory nerve in its first section occur most often in the autumn-winter period, when there is a massive incidence of acute respiratory infections and influenza. Prolonged course of the disease can cause a complete loss of smell. Recovery of nerve function 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, the ENT prescribes physiotherapy:
- microwave therapy for the nose and sinuses;
- ultraviolet irradiation of the nasal mucosa, with a power of 2-3 biodoses;
- magnetic therapy 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 ways and the last two. This speeds up the recovery of lost functions. After clinical recovery, the following physiotherapy treatment is also carried out for rehabilitation:
- electrophoresis using "No-shpa", "Prozerin", as well as nicotinic acid or lidase;
- ultraphonophoresis of the nose and maxillary sinuses for ten minutes daily;
- irradiation with a red laser spectrum;
- endonasal electrical stimulation.
Each course of therapy is carried out up to ten days with breaks of fifteen to twenty days until the function of the olfactory nerve is fully restored.
