Cranial Pair II: The Optic Nerves

The optic nerves (ONs), one of the 12 pairs of cranial nerves (Pair II), together with the olfactory and the cochlear nerves, are devoted to transmit sensory inputs. In particular, ONs convey visual information from the retina to the brain. In mammals, the ONs are bilateral structures that extend from the optic disc to the optic chiasm containing glial cells and retinal ganglion cells (RGCs) axons. RGCs are the only retinal neurons able to collect visual information and transmit it to the visual centers in the brain for its processing and integration with the rest of sensory inputs. During embryonic development, RGCs born in the retina extend their axons to exit the eye and follow a stereotypic path outlined by the transient expression of a wide set of guidance molecules. As the rest of central nervous system structures, the ONs are covered with myelin produced by oligodendrocytes and wrapped by the meninges. ON injuries or RGCs degenerative conditions may provoke partial or complete blindness because they are incapable of spontaneous regeneration. Here, we first review major advances on the current knowledge about the mechanisms underlying the formation of the ONs in mammals. Then, we discuss some of the human disorders and pathologies affecting the development and function of the ONs and finally we comment on the existing view about ON regeneration possibilities. Anat Rec, 302:428-445, 2019. © 2018 Wiley Periodicals, Inc.