Cranial Nerves + The Eye (3rd copy) PDF
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Uploaded by EnterprisingNonagon
Monash University Malaysia
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Summary
This document details the anatomy and physiology of the optic nerve, including its course from the retina to the visual cortex. It covers various lesions and their effects on visual field. The explanations include diagrams, charts, and descriptions that illustrate various aspects of this important system.
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CN II: Optic Nerve Function: Special somatic sensory only → Vision Course: HIGH YIELD Extracranial: Light is detected by the photoreceptors of the eye (rods and cones) These receptors stimulate retinal ganglion cells which converge to form the optic nerve This travels through the o...
CN II: Optic Nerve Function: Special somatic sensory only → Vision Course: HIGH YIELD Extracranial: Light is detected by the photoreceptors of the eye (rods and cones) These receptors stimulate retinal ganglion cells which converge to form the optic nerve This travels through the optic canal to enter the cranial cavity Lesion #1: Damage at the optic nerve = Monocular blindness Intracranial: Within the middle cranial fossa, the two optic nerves form the optic chiasm (close proximity to pituitary) Lesion #2: At the optic chiasm = bilateral hemianopia Important to know that this can be caused by a pituitary adenoma compressing on the optic chiasm CN II: Optic Nerve Intracranial continued: Here, the fibres from the nasal/medial half of each side cross to the contralateral optic tract while the fibres from the temporal/lateral halves remain ipsilateral ○ Left optic tract: transmits the right FOV ○ Right optic tract: transmits the left FOV Lesion #3: At the optic tract = contralateral homonymous hemianopia Each optic tract travels to the lateral geniculate nucleus in its corresponding cerebral hemisphere Lesion #5: At the lateral geniculate nucleus (affecting both optic radiations) = contralateral homonymous hemianopia CN II: Optic Nerve Intracranial continued: They then synapse before dividing into: ○ Upper optic radiation: transmits lower quadrant FOV, travels through the parietal lobe to the upper bank of the calcarine fissure ○ Lesion #6: At the upper optic radiation = contralateral inferior quadrantanopia ○ Lower optic radiation (Meyer’s loop): transmits upper quadrant FOV, travels through the temporal lobe to the lower bank of the calcarine fissure ○ Lesion #4: At the lower optic radiation = contralateral superior quadrantanopia These converge at the visual cortex Lesion #7: At the visual cortex = contralateral homonymous hemianopia with macular sparing There are two theories for why macular sparing occurs: ○ Vascular: Dual supply to the occipital pole by the MCA and PCA ○ Cortical: Dual representation of the macular in both occipital cortices
