Smell

synonym

Smell, organ of smell

anatomy

The cells that are responsible for smelling, the olfactory cells, are located in the olfactory mucosa. This is very small in humans and is located in the Regio olfactoria (olfactory fissure), a narrow part of the upper nasal cavity. It is limited by the upper turbinate and the opposite nasal septum.

The olfactory epithelium is built up in several rows: the furthest outer layer is made up of Support cells formed, followed by the actual layer Sensory cells. The deepest cell layer is covered by the Basal cells built, which also as Stem cells function and serve to regenerate the sensory cells. The lifetime of the sensory cells is about 30 - 60 days. Overall there is in the nose approx. 10 million sensory cells. They have tiny 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 is transmitted via the olfactory epithelial processes that connect the olfactory nerve (Olfactory nerve) form, for Olfactory bulb reach. There the nerves are connected and the stimulus is passed on to the olfactory cortex and other areas in the brain.

It is also important that in addition to the sensory cells just mentioned, the olfactory region also contains sensory fibers from another nerve that react to non-aromatic, pungent odor stimuli such as ammonia. These are fibers of the trigeminal nerve.

Odor 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 designated. It is not so easy to distinguish from it Hyposmia, decreased odor perception. The Hyperosmia on the other hand denotes the increased perception of smells. The complete failure of the olfactory organ is called Anosmia. The above terms are assigned to the quantitative olfactory sensations.

To the qualitative olfactory sensations (Dysosmia) counting: Parosmia (distorted / wrong smell sensation), Cacosmia (wrong perception as lazy / uncomfortable), Heterosmia (Inability to distinguish smells), Agnosmia (Inability to recognize perceived smells) Phantosmia (Hallucination of smells).

Etiology:
The acute viral rhinitis is probably the most common cause of a decrease in the ability to smell. The reason is that increased secretion production and the swollen Mucous membranesthat relocates the roof of the nose, the area in which the olfactory epithelium is located.

The Viruses can also directly damage the sensory cells and a persistent olfactory disorder cause. In everyday clinical practice, a previous influenza infection is one of the most common causes of anosmia.

Also one allergic rhinitis or the nonspecific hyperreactive rhinopathy can be a swollen Nasal mucosa and cause associated hyposmia.

Polyp formation due to a chronic sinus infection (Sinusitis) often leads to an obstruction of the olfactory cleft and hyposmia, up to anosmia.

Other causes of hyposomy or anosmia include:

toxic solvents or Medication, Zinc deficiency, Tumors like the aesthetic neuroblastoma or Meningiomas, Tearing off the filae olfactoriae (fine fibers of the olfactory nerve) due to a Cranial brain trauma, central transmission or degenerative diseases (Alzheimer's disease), inherited disordersleading to selective hyposmia or anosmia and that Kallmann syndrome. A loss of the sense of smell and neuroendocrine disorders can occur.

Diagnosis of olfactory disorders: It is important to have a specific anamnesis, a normal odor test and an objective test of the olfactory sense using olfactory evoked potentials. Other 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 frontal base, as well as an MRI of the skull.

Therapy: Knowledge of the primary causes is a prerequisite for a causal and successful therapy for olfactory disorders.

Clinical examination

During a clinical olfactory examination, the patient is asked to close his eyes. One then holds him so-called "sniffin ‘sticks“Under the nose, these are pens that have a characteristic fragrance.

Mainly be aromatic substances with characteristic smells such as peppermint, coffee, or clove oil that the patient should identify. It must be ensured that the smells are presented per nostril, i.e. separately from each other. Now the patient has to indicate whether and what he smells. If the patient does not report any odor perception of the aromatic fragrances, a non-aromatic substance such as ammonia tested.