The paired olfactory nerve or olfactory nerve (from Latin olfactus 'smell') - often also in the plural: the Nn. olfactorii - is also called the first cranial nerve , N. I and consists of around twenty short fiber bundles on each side. As sensory (special viscero afferent ) fibers, they conduct the signals from the olfactory cells in the olfactory mucous membrane of the nose to the part of the brain, which is the olfactory bulb ( bulbus olfactorius ) on each side and belongs to the telencephalon (cerebrum), and thus enable olfactory perception (see also olfactory cortex and olfactory brain ).
The fine fibers of the nerve ( fila olfactoria ) run as axons of the cells of the olfactory mucosa in the upper part of the nose through the lamina cribrosa of the ethmoid bone ( os ethmoidale ) to the olfactory bulb directly above it . After switching to mitral and tuft cells in this structure, the impulses are passed on via the olfactory tract . This is divided into the stria olfactoria lateralis and the stria olfactoria medialis . The lateral ones run to the primary olfactory cortex in the telencephalon, the prepiriformis area (Brodmann area 28) and the amygdala , while the medial ones are passed on to the limbic system, among other things. This means that the olfactory sensory impressions are the only ones that are not connected in the thalamus before they reach the cortex.
The cells of the olfactory mucosa are so-called primary sensory cells , which project into the central nervous system without being connected . Since, by definition, the point of projection of the first neurons is a cranial nerve nucleus , but the fibers of the olfactory nerve run to the olfactory bulb without being connected in a sensory ganglion , this is sometimes regarded as the "cranial nerve equivalent".
Like the optic nerve ( optic nerve ), the olfactory nerve is not a cranial nerve in the actual sense, but an upstream part of the brain. These two also differ from the actual cranial nerves in that they do not arise from the brain stem .
Different fragrances are presented to the patient and should be named as precisely as possible.