Corpus: Olfactory nerves
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Synonyms: olfactory nerves, olfactory nerve, 1st cranial nerve, Nervus I
English: , olfactory fibres, CN I
Definition[Bearbeiten]
The fila olfactoria are special viscerosensitive, fine nerve fibres that serve the perception of odours. According to traditional understanding, the fila olfactoria in their entirety are also referred to as the olfactory nerve or 1st cranial nerve.
Background[Bearbeiten]
The olfactory nerve is not a cranial nerve in the strict sense, as it is an upstream part of the brain, like the optic nerve. It also does not originate in the brain stem, like cranial nerves III to XII.
Anatomy[Bearbeiten]
The fila olfactoria are about 20-25 small bundles of medullary nerve fibres. They are axons of the primary sensory cells of the olfactory epithelium and form the first section of the olfactory pathway. The fibres conduct the electrical impulses of the olfactory cells from the regio olfactoria of the nasal mucosa through the lamina cribrosa of the ethmoid bone (Os ethmoidale).
Intracranially, the fila olfactoria end predominantly at dendrites of mitral cells in the olfactory bulb. The impulses are then transmitted via the olfactory tract to the primary olfactory cortex in the telencephalon.
Due to its course, the olfactory nerve is the shortest cranial nerve.
Histology[Bearbeiten]
A special feature of the fila olfactoria are the olfactory ensheathing cells (OECs). They are classified as macroglia and are similar to Schwann cells, but do not form myelin sheaths around the axons. The OECs bundle the axons of the olfactory cells into fascicles, to which newly sprouting axons orientate themselves as they grow towards the olfactory bulb. In this way, they support the continuous regeneration of the fila olfactoria, which is necessary due to the limited lifespan of the olfactory cells of 6 to 8 weeks.
Embryology[Bearbeiten]
The fila olfactoria are of ectodermal origin and form from the embryonic nasal placode.
Clinic[Bearbeiten]
Diagnostics[Bearbeiten]
- Imaging (CT, MRT)
- Functional tests (olfactometry)
Diseases[Bearbeiten]
Damage to the fila olfactoria leads to a restriction of the sense of smell, which manifests itself as hyposmia or anosmia. A fracture of the base of the skull or other craniocerebral trauma can lead to the fila olfactoria being torn off.
The nerve fibres of the fila olfactoria establish a connection between the nasal cavity and the brain, via which nanoparticles and pathogens can reach the intracranial cavity, for example in the case of naegleriasis.
Tumours originating from the fila olfactoria are rare. These include olfactory neurocytoma, olfactory neuroblastoma and olfactory neuroepithelioma.