The optic nerve (CN II) is the second cranial nerve, responsible for transmitting the special sensory details for vision.
You are watching: Fibers from the medial side of each eye cross over to the opposite side of the brain at the
It is emerged from the optic vesicle, an outpocketing the the forebrain. The optic nerve can therefore be considered component of the main nervous system, and also examination that the nerve enables an evaluate of intracranial health.
Due to its distinct anatomical relation to the brain, the optic nerve is surrounded by the cranial meninges (not by epi-, peri- and endoneurium like many other nerves).
In this article, us shall look at the anatomy of the optic nerve – that course, sensory functions and clinical relevance.
Fig 1 – synopsis of the anatomical course of the optic nerve.
The anatomical course of the optic nerve defines the transmission of special sensory information from the retina the the eye to the main visual cortex that the brain. It deserve to be split into extracranial (outside the cranial cavity) and intracranial components.
The optic nerve is developed by the convergence the axons from the retinal ganglion cells. These cells in turn receive impulses indigenous the photoreceptors that the eye (the rods and cones).
After that formation, the nerve leaves the bony orbit via the optic canal, a passageway with the sphenoid bone. It enters the cranial cavity, running along the surface of the middle cranial fossa (in close proximity come the pituitary gland).
Intracranial (The visual Pathway)
Within the center cranial fossa, the optic nerves from every eye hold together to type the optic chiasm. In ~ the chiasm, fibres from the nasal (medial) fifty percent of every retina cross over to the contralateral optic tract, when fibres indigenous the temporal (lateral) halves stay ipsilateral:Left optic tract – has fibres from the left temporal (lateral) retina, and the ideal nasal (medial) retina.Right optic tract – contains fibres native the ideal temporal retina, and also the left nasal retina.
Fig 2 – The nasal retinal fibres crossing end at the optic chiasm.
Each optic tract travels to its matching cerebral hemisphere to reach the lateral geniculate cell nucleus (LGN), a relay system located in the thalamus; the fibres synapse here.
Axons indigenous the LGN then carry visual information via a pathway recognized as the optic radiation. The pathway itself deserve to be split into:Upper optic radiation – carries fibres native the remarkable retinal quadrants (corresponding come the inferior visual field quadrants). It travels through the parietal lobe to with the intuitive cortex.Lower optic radiation – carries fibres native the inferior retinal quadrants (corresponding to the superior visual ar quadrants). That travels with the temporal lobe, via a pathway known as Meyers’ loop, to reach the visual cortex.
Once in ~ the intuitive cortex, the brain processes the sensory data and also responds appropriately.
Fig 3 – The optic pathway.
Fig 4 – Bitemporal hemianopia, influence the lateral visual fields in both eyes.
A pituitary adenoma is a tumour of the pituitary gland. In ~ the middle cranial fossa, the pituitary gland lies in close proximity come the optic chiasm. Enlargement that the pituitary gland deserve to therefore affect the to work of the optic nerve.
Compression to the optic chiasm particularly affects the fibres that space crossing over from the nasal fifty percent of every retina. This produces visual defect affecting the peripheral vision in both eyes, recognized as a bitemporal hemianopia.
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Surgical intervention is typically required. To access the gland, the surgeon provides a transsphenoidal approach, accessing the gland via the sphenoid sinus.