Brain

Visual Information

  • Eye
    • Photoreceptors are unevenly distributed across the retina
    • The retina processes the visual information before sending to the brain
    • The retina is organized into three function stages:
      • photoreception
        • photoreceptors
      • internal transmission
        • horizontal cells, amacrine cells
      • output
        • retina ganglial cells: produce action potentials
    • Output neurons of the retina: retinal ganglion cells
    • Rods: detect low light level
      • 498 nms
      • Used on scotopic (night) vision
    • Cones: high light level and colors
      • finer detail
      • rapid changes
      • S cones: blue light, 420 to 440 nm waves
      • M cones: green light, 535, 550
      • L cones: red light, 565 to 580 nm
      • GPCR protein photopsin, differs on each cone
      • Thricromat vision
      • There are tetrachromats animals (and humans :O)
      • photopic vision
    • 20:1 rods to cones
    • Photoreceptors do phototransduction
      • retinal + opsin = rhodopsin (form of vitamine A)
      • When a photon is absorbed by a retinal, the shape of the retinal changes from 11-cis retinal to all-trans retinal. Cis and Trans related to position
      • Photoreceptors hyperpolarize when light hits them, stopping the release of neurotransmitters when illuminated.
    • Receptive field
      • ON Center
      • OFF Center
    • Direct Pathway
      • OFF Bipolar cells
        • glutamate reaches bipolar cells and cell depolarizes
        • light off
      • ON bipolar cells
        • glutamante reaches , gpcrs cause cell to hyperpolarize
        • light on
    • Lateral Pathway
    • photoreceptors
      • dark, open ion channels = depolarizes
      • light, close ion channels = hyperpolarizes
    • retinofugal pathway
      • nerves cross (left to right, right to left)
      • In order:
        • optic nerve
        • optic chiasma
          • nerves from both eyes combine
        • optic tract
        • lateral geniculate nucleus (LGN)
          • About 80% of excitatory synapses found in the LGN come back from the visual cortex
          • dorsal lateral part of thalamus
          • left hemisphere processes right and vice-versa
          • 6 layers: parallell processing
          • koniocellular layers: color
        • Ventral pathwway (what):
          • Receptive field size and stimulus complexity increase
        • Dorsal pathway (where, how):
          • sensitivity to motion (MT), ocular dominance
        • optic radiation
        • visual cortex
          • 6 sheets of paper, 6 layers
          • Primary Visual Cortex (V1)
            • input: speicifc layers of structure
            • layer 4: magnocellullar and parvocellular input from lgn
            • 2 & 3 : koniocellular cells from lgn
            • edge detectors
      • retinotectal projection - tectum
      • accessory optic system
      • thalamus –> visual cortex