Olfactory Nerve (CN I)

Function: Special sensory (special visceral afferent) - that is, the special sense of smell. "Olfaction is the sensation of odors that results from the detection of odorous substances aerosolized in the environment".

The cell bodies of olfactory receptor neurons are located in the olfactory organ (the olfactory part of the nasal mucosa or olfactory area), which is located in the roof of the nasal cavity, and along the nasal septum and medial wall of the superior nasal concha. Olfactory receptor neurons are both receptors and conductors. The apical surfaces of the neurons possess fine olfactory cilia, bathed by a film of watery mucus secreted by the olfactory glands of the epithelium. The olfactory cilia are stimulated by molecules of an odiferous gas dissolved in the fluid.

The basal surfaces of the bipolar olfactory receptor neurons of the nasal cavity of one side give rise to central processes that are collected into approximately 20 olfactory nerves (Latin fila olfactoria), constituting the right or left olfactory nerve (CN I). They pass through tiny foramina in the cribriform plate of the ethmoid bone, surrounded by sleeves of dura mater and arachnoid mater, and enter the olfactory bulb in the anterior cranial fossa. The olfactory bulb lies in contact with the inferior or orbital surface of the frontal lobe of the cerebral hemisphere. The olfactory nerve fibers synapse with mitral cells in the olfactory bulb. The axons of these secondary neurons form the olfactory tract. The olfactory bulbs and tracts are anterior extensions of the forebrain.

Each olfactory tract divides into lateral and medial olfactory striae (distinct fiber bands). The lateral olfactory stria terminates in the piriform cortex of the anterior part of the temporal lobe, and the medial olfactory stria projects through the anterior commissure to contralateral olfactory structures. The olfactory nerves are the only cranial nerves to enter the cerebrum directly.