Olfactory Nerve (First Cranial Nerve)
The olfactory nerve (CN I) originates from small olfactory receptors in the mucous membrane of the nose. Unmyelinated CN I fibers pass from these receptors in the nasal cavity through the cribriform plate of the ethmoid bone and enter the ventral surface of the olfactory bulb, where they form the nerve.
The olfactory tract runs posteriorly from the bulb beneath the frontal lobe of the brain in a groove (or sulcus) and lateral to the gyrus rectus (Fig 3-3). The gyrus rectus forms the anterolateral border of the suprasellar cistern. Meningiomas arising from the arachnoid cells in this area can cause important ophthalmic signs and symptoms associated with loss of olfaction.
Figure 3-1 View from the right parietal bone looking downward into the skull base. Various anatomical relationships are shown at the base of the skull. The orbits are located to the right, out of the picture (the roof of the orbits is just visible). The floor of the right middle cranial fossa is in the lower part. A, The relationship between the bony canals is shown. AC = anterior clinoid; ACF = anterior cranial fossa; CC = carotid canal; FO = foramen ovale; FR = foramen rotundum; MCF = middle cranial fossa; OF = optic foramen; PC = posterior clinoid; SOF = superior orbital fissure; ST = sella turcica. B, The relationship between the cranial nerves (with trigeminal ganglion) is depicted. I = olfactory nerve; II = optic nerve; III = oculomotor nerve; IV = trochlear nerve; V = trigeminal nerve, with ophthalmic (V1), maxillary (V2), and mandibular (V3) divisions; VI = abducens nerve; TG = trigeminal ganglion. C, The relationship between the arteries is demonstrated. ACoA (and arrowhead) = anterior communicating artery; BA = basilar artery; ICA = internal carotid artery; MCA = middle cerebral artery; OA = ophthalmic artery; PCA = posterior cerebral artery; PCoA = posterior communicating artery; II = optic nerve.
(Reproduced with permission from Zide BM, Jelks GW, eds. Surgical Anatomy of the Orbit. New York: Raven; 1985.)
A, Intra-axial course of the ocular motor nerves at the level of the midbrain (above) and pons (below). Note the relationship to the surrounding cerebellum and cranial nerves (CNs) V and VII. B, Schematic of CNs II–VI from the brainstem to the orbit.
(Part A illustration by Craig A. Luce. Part B modified with permission from Friedman NJ, Kaiser PK, Trattler WB. Review of Ophthalmology. 3rd ed. Edinburgh: Elsevier; 2018:63.)
A, Schematic of the optic chiasm and brainstem. B, Photograph of the optic chiasm (arrow) in a human brain. CN I = olfactory nerve; CN III = oculomotor nerve; CN V = trigeminal nerve; CN VI = abducens nerve; Ob = olfactory bulb.
(Modified with permission from Liu GT, Volpe NJ, Galetta SL. Neuro-Ophthalmology: Diagnosis and Management. 2nd ed. New York: Elsevier; 2010:238.)
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.