The olfactory nerve (first cranial nerve, CN I, Latin: nervus olfactorius) is considered as the first cranial nerve, although it is actually a collection of the olfactory receptor cell axons and is derived from the telencephalon. The olfactory nerve is purely sensory in function and transmits the sense of smell.
The olfactory nerve originates in the nasal mucosa on the upper part of the nasal cavity as special sensory cells (neurosensory cells of the mucosa), which are the first-order neurons in the olfactory pathway. There are around 3 million receptor cells in the olfactory epithelium supplemented with supporting cells and the ducts of the Bowman`s glands. The axons of the olfactory receptor cells continue as small nerve fascicles (olfactory fila), which in gross anatomy is referred to as the olfactory nerve, passing through the cribriform plate of the ethmoid bone and reach the olfactory bulb of the brain, where the second-order neurons are located. The axons of the second-order cells form the olfactory tract that serves as a connection between the olfactory bulb and the cerebral hemispheres. It continues as the olfactory trigone that lies in the olfactory groove of the frontal lobe. In the trigone, the fibers separate into olfactory stria, which synapse with the third-order neurons in the perforated substance. The axons of the third-order neurons reach the olfactory cortex, and also synapse with the components of the limbic system. The lateral olfactory striae project to uncus, but the medial olfactory striae project to hypothalamus and brainstem nuclei.