Visual cortex

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  1. Stimuli from the right visual field projects upon the left retinal field of both eyes and vice versa; stimuli from the upper visual fields project upon the lower retinal fields of both eyes and vice versa
    1. light is detected by rods and cones that synapse on bipolar cells and may have their transmission modulated by interneurons
      1. synapses between bipolar cells and ganglion cells have transmission influenced by amacrine cell interneurons and horizontal cells (inhibit adjacent cells)
    2. ganglion cells give rise to optic nerve fibers
  2. retinotopic organization is preserved within the optic nerves
  3. in the optic chiasm, temporal retinal fibers occupy the lateral chiasm to enter the ipsilateral optic tract while nasal retinal fibers cross in the central chiasm to enter the contralateral optic tract so that all visual sensory input from the right visual field enters the left optic tract and vice versa
    1. Willibrand’s knee is a piece of the contralateral optic nerve than bends into the ipsilateral optic nerve before heading out the ipsilateral optic tract; a lesion of Willibrand’s knee can cause an ipsilateral junctional scotoma in association with an upper quadrantaopia on the opposite side of the lesion due to interruption of nasal fibers from the opposite side into the optic nerve of the ipsilateral side – See Figure 8
  4. as the optic tract approaches the lateral geniculate body it rotates internally about 90 degrees so that the superior retinal fibers project onto the medial portion of the lateral geniculate and the inferior retinal fibers project onto the lateral protion of the lateral geniculate, and the macular fibers occupy and intermediate position; some genicualte fibers project to the pulvinar
  5. the lateral geniculate neurons project axons to the primary visual cortex over the optic radiations; those representing the inferior retinal fields project forward into the temporal lobe forming Meyer’s loop then turn laterally above the inferior horn of the lateral ventricle and posteriorly to form the inferior portion of the optic radiations; those axons representing the upper retinal fields project directly laterally where they pass anterior to the atrium of the lateral ventricle before turning posteriorly to form the upper protion of the optic radiations
  6. the primary visual cortex (Brodmann’s area 17) is organized with the upper retinal fibers ending in the upper lip of the calcarine fissure and lower retinal fibers ending in its lower lip; the peripheral retina is represented most anteriorly while the macula is more postierorly represented at the occipital pole
    1. cortical cells are sensitive to contours (edges and lines) and the spatial orientation of those contours
  7. visual association cortex (Brodmann’s area 18 and 19) surrounding the primary visual cortex on both the medial and lateral aspects of the hemisphere and receives input from both the primary visual cortex and pulvinar
  8. a lesion of the right inferior occipitotemporal region sparing the optic radiation and striate cortex will cause a pure achromatopsia
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