Cranial nerve ii

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Cranial nerve ii

  1. 1. OPTIC NERVE
  2. 2. Begins at the optic disc Pierces tunic of eyeball 3mm nasal to posterior pole
  3. 3. <ul><li>Functional components: </li></ul><ul><li>Special somatic afferents </li></ul><ul><li>Afferents for optical reflexes </li></ul><ul><li>Peculiarities: </li></ul><ul><li>Prolongation of white mater </li></ul><ul><li>Covered by meninges </li></ul><ul><li>Pial sheath carrying blood vessels project into substance </li></ul><ul><li>Devoid of neurilemmal sheath </li></ul><ul><li>Myelination by oligodendrocytes </li></ul>
  4. 4. <ul><li>Course: </li></ul><ul><li>Intra-orbital part </li></ul><ul><li>Canalicular part </li></ul><ul><li>Intra-cranial part </li></ul><ul><li>Lesion: </li></ul><ul><li>Total blindness ipsilateral eye </li></ul><ul><li>Loss of ipsilateral direct and contralateral consensual pupillary light reflex </li></ul><ul><li>Retention of ipsilateral consensual and contralateral direct light reflex </li></ul><ul><li>Unaffected accommodation reflex </li></ul>
  5. 5. VISUAL PATHWAY Principles
  6. 6. <ul><li>Receptors: </li></ul><ul><li>Rods </li></ul><ul><li>Cones </li></ul><ul><li>Neurons: </li></ul><ul><li>First order: bipolar cells </li></ul><ul><li>Second order: ganglion cells </li></ul><ul><li>Third order: LGB </li></ul>Visuo-striate area (17): Both walls of calcarine sulcus involving Cuneus and lingual gyrus
  7. 8. VISUAL PATHWAY Components
  8. 9. Visual Pathway
  9. 10. Visual Pathway <ul><li>Optic chiasma: </li></ul><ul><li>Junction of the floor and the anterior wall of the third ventricle </li></ul><ul><li>Rests on the diaphragma sellae </li></ul><ul><li>Wilbrand’s loop </li></ul>
  10. 11. Visual Pathway <ul><li>Optic tracts: </li></ul><ul><li>Medial root </li></ul><ul><ul><li>Gudden’s commisure </li></ul></ul><ul><li>Lateral root </li></ul><ul><ul><li>LGB </li></ul></ul><ul><ul><li>Superior colliculus & pre-tectal nucleus </li></ul></ul><ul><ul><li>Supra-chiasmatic nucleus </li></ul></ul>
  11. 12. Visual Pathway <ul><li>Lateral geniculate body: </li></ul><ul><li>Part of meta-thalamus </li></ul><ul><li>Connected to superior colliculus via superior brachium </li></ul><ul><li>Cells arranged in six layers </li></ul>
  12. 13. Visual Pathway <ul><li>Optic radiation: </li></ul><ul><li>From LGB to striate area of visual cortex (17) </li></ul><ul><li>Passes through the retro-Lentiform part internal capsule </li></ul><ul><li>Meyer’s loop </li></ul>
  13. 14. Pupillary light reflex Direct Consensual
  14. 15. Accommodation
  15. 16. Accommodation reflex
  16. 17. VISUAL PATHWAY Lesions
  17. 18. Lesions
  18. 19. Lesions
  19. 21. 1 = Central scotoma secondary to optic neuritis 2 = Total blindness of the right eye from a complete lesion of the right optic nerve 3 = Bitemporal hemianopia from a complete lesion of the optic chiasm 4 = Right nasal hemianopia from a perichiasmal lesion 5 = Right homonymous hemianopia from a complete left optic tract lesion 6 = Right homonymous superior quadrantopia caused by partial involvement of the optic radiation in the left temporal lobe (Meyer's loop) 7 = Right homonymous inferior quadrantopia caused by partial involvement of the optic radiation in the left parietal lobe 8 = Right homonymous hemianopia from a complete lesion of the left optic radiation 9 = Right homonymous hemianopia (with macular sparing) from a posterior cerebral artery occlusion causing ischemia of the calcarine cortex of the occipital lobe

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