Synonym
Smell, olfactory organThe cells responsible for smell, the olfactory cells, are located in the olfactory mucosa. This is very small in humans and is located in the olfactory region, a narrow part of the upper nasal cavity. It is bordered by the upper nasal concha and the opposite nasal septum.
The olfactory epithelium has a multi-rowed structure: the outermost layer is formed by supporting cells, followed by the layer of the actual sensory cells. The deepest cell layer is formed by the basal cells, which also function as stem cells and serve to regenerate the sensory cells. The lifetime of the sensory cells is about 30 – 60 days.
In total there are about 10 million sensory cells in the nose. They have small olfactory hairs that protrude into the olfactory epithelium and are responsible for absorbing molecules from the air we breathe. The molecules trigger a stimulus that reaches the olfactory bulb via the olfactory epithelial sites that form the olfactory nerve (nervus olfactorius).
There the nerves are interconnected and the stimulus is transmitted to the olfactory cortex and other areas of the brain. It is also important that, in addition to the sensory cells just mentioned, the olfactory region also contains sensitive fibers of another nerve that react to non-aromatic, pungent odor stimuli such as ammonia. These are fibers of the trigeminal nerve.
Odour disorders and their causes
The sense of smell can be divided into normal, quantitative and qualitative perception of the smell. Normal smelling is called normosmia. Hyposmia, the reduced olfactory perception, is not so easily distinguished from it.
Hyperosmia, on the other hand, refers to the increased perception of odours. The complete failure of the olfactory organ is called anosmia. The above mentioned terms are assigned to the quantitative olfactory sensations.
Qualitative olfactory sensations (dysosmia) are included: Parosmia (distorted/false olfactory sensation), cacosmia (false perception as lazy/unpleasant), heterosmia (inability to distinguish odours), agnosmia (inability to recognize perceived odours), phantosmia (hallucination of odours) Etiology: Acute viral rhinitis is probably the most common cause of a decrease in the ability to smell. The reason for this is the increased production of secretions and the swollen mucous membranes that displace the nasal roof, the area where the olfactory epithelium is located. The viruses can also directly damage the sensory cells and cause a persistent olfactory disorder.
In everyday clinical practice, a previous influenza infection is one of the most common causes of anosmia. Allergic rhinitis or non-specific hyperreactive rhinopathy can also cause a swollen nasal mucosa and associated hyposmia. The formation of polyps due to chronic sinusitis (inflammation of the paranasal sinuses) often leads to a shifting of the olfactory cleft and hyposmia, up to and including anosmia.
Other causes of hyposomia or anosmia are: toxic solvents or drugs, zinc deficiency, tumors such as aesthioneuroblastoma or meningiomas, tearing of the filae olfactoriae (fine fibers of the olfactory nerve) due to craniocerebral trauma, central transmission or degenerative diseases (Alzheimer’s disease), inherited disorders leading to selective hyposmia or anosmia, and Kallmann syndrome. This can lead to a loss of sense of smell and neuroendocrine disorders. Diagnosis of olfactory disorders: Important is a specific anamnesis, a normal olfactory test, as well as an objective examination of the sense of smell using olfactory evoked potentials. Further necessary additional diagnostics are the measurement of the zinc concentration in the serum, a neurological status, a CT (computer tomography) of the paranasal sinuses and frontobasis, as well as an MRI of the skull. Therapy: Knowledge of the primary causes is a prerequisite for a causal and successful therapy of olfactory disorders.
