The Retina

1. Fundus

   Anmerkungen:

   • Plural; fundi
   1. Define: the back layer of the retina
2. Blind Spot
   1. Define: small area of the retina where the optic nerve emerges.

      Anmerkungen:

      • Therefore, this area contains no receptor cells
      • This area is called the optic disk. - The area where: -> Axons leave the eye -> Blood vessels enter the eye
      1. Optic nerve
         1. An axon bundle from the ganglion cells (the last layer) in the retina
   2. Why do we not notice our blind spot in our visual field?

      Anmerkungen:

      • Answer: Our brain "fills in" our blind spot with the information from the surrounding areas. 
3. Pigment Epithelium
   1. Purpose: Provides vital nutrients to the photoreceptors
      1. The epithelium holds reserve pigment molecules that the photoreceptors use to detect light rays
   2. Are opaque

      Anmerkungen:

      • aka not transparent.  - Hence, it is a dark layer. It absorbs most light photons that do not get absorbed by receptor cells
      1. SIDE: Cool things about Cats

         Anlagen:

         • Week One: The Retina
   3. Define: thin layer of cells between the retina and the sclera

Anmerkungen:

• There are 5 major classes of neurons. 
• 3 Layers 2nd layer:  - [contain the cells in 'orange']  -> are intermediate neurons - Transform raw light information [from the photoreceptors] o neural energy 
• Fig 2.7 - pg 37
• There are two pathways [from lecture notes]

1. 1. Photoreceptors
   1. Define: Are light-sensitive neurons [in the retina]

      Anmerkungen:

      • So they respond directly to light rays
      1. Are special type of neurons

         Anmerkungen:

         • Contain no dendrites
   2. Two types

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      • Week One: The Retina
      1. Rods
      2. Cones
   3. Each photoreceptor has one of the four types of visual pigments
      1. Visual Pigment Molecules
         1. Consist of
            1. A protein (an opsin); and
               1. Determines what wavelength of light a photoreceptor absorbs
               2. When they are struck by light -> they change in structure

                  Anlagen:

                  • Week One: The Retina
            2. A chromophore
               1. Captures light
      2. Melanopsin

         Anlagen:

         • Week One: The Retina
2. 2. Horizontal Cells

   Anmerkungen:

   • A specialized retinal cell that contacts both photoreceptor and bipolar cells. 
   1. Location

      Anmerkungen:

      • Are the cells sandwiched between photoreceptors and bipolar cells
   2. Purpose

      Anmerkungen:

      • 1. Gather light information from several receptors 2. Process light information via a mechanism - lateral inhibition  -> Thus, they have lateral connections
   3. Side-Note

      Anmerkungen:

      • Are crucial in the construction of the centre-surround receptive fields. 
3. 3. Bipolar Cells

   Anmerkungen:

   • Define: a retinal cell that synapses with either rods or cones (not both( and with horizontal cells. It then passes the signals on to the ganglion cells
   1. Location

      Anmerkungen:

      • The bridge between photoreceptors and ganlion cells
   2. Two types

      Anlagen:

      • Week One: The Retina
4. 4. Amacrine Cells

   Anmerkungen:

   • A retinal cell - makes synaptic contacts with bipolar cells, ganglion cells and other amacrine cells.  - Part of the lateral pathway. [horizontal]  - in the inner synaptic layer
   1. Purpose

      Anmerkungen:

      • Is less well understood
      • Appear to: - integrate information from groups of bipolar cells, and - communicate these computations to ganglion cells. 
5. 3. Ganglion Cells

   Anmerkungen:

   • A retinal cells that: [kind of like the purpose!]  - receives visual information from photoreceptors via two intermediate neuron types (bipolar cells and amacrine cells); and - sends that information to the brain and the midbrain
   1. Purpose
      1. Communicate between the eye and the brain
         1. RECEIVE information from bipolar and amacrine cells via dendritic synapse; then
         2. SEND information to the LGN via the optic nerve
   2. Two types

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      • Week One: The Retina
   3. Receptive Fields

      Anlagen:

      • Week One: The Retina

Anmerkungen:

• Gives a detailed view of the structure of the retina

Anmerkungen:

• They pass through the cells in the retina to reach the photoreceptors [which are the farthest layer of cells from the pupil].  -> The cells are almost completely transparent, so the light usually passes through them.