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Ocular Anatomy and Physiology > Week 12: Retina and Visual Pathway > Flashcards

Week 12: Retina and Visual Pathway Flashcards

1
Q

List the retinal layers from anterior to posterior (hint: 10)

A
  1. Retinal pigment epithelium
  2. Photoreceptors (rods and cones)
  3. Outer limiting membrane
  4. Outer nuclear layer
  5. Outer plexiform layer
  6. Inner nuclear layer
  7. Inner plexiform layer
  8. Ganglion cell layer
  9. Nerve fibre layer
  10. Inner limiting membrane
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2
Q

Describe the retina

A
  • Retinal photoreceptors act as transducers

- Converts absorbed electromagnetic radiation into a neural signal

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3
Q

List three functions for the retina/visual system

A
  • Spatial discrimination
  • Colour discrimination (trichromatic)
  • Detection of movement
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4
Q

Describe the rods and cones functions of the following: Peak Responsiveness, Amplification, Direction of light, Visual acuityFovea / Periphery & Colour vision

A

Rods:

  • Peak Responsiveness = low light levels
  • Amplification = high
  • Direction of light = sensitive to scattered light
  • Visual acuity = low
  • Fovea / Periphery = not present / concentrated
  • Colour vision = no – achromatic (one type of rod pigment)

Cones:

  • Peak Responsiveness = high light levels
  • Amplification = low
  • Direction of light = sensitive to direct axial rays
  • Visual acuity = high
  • Fovea / Periphery = concentrated/low
  • Colour vision = yes – chromatic (three types of cone pigment)
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5
Q

List the dimensions for a retinal fundus

A
  • Macula 5.5 mm in diameter
  • Fovea 1.5 mm in diameter
  • Foveola 0.35 mm in diameter
  • Optic Nerve Head: 1.5 mm Horizontal, 2 mm Vertical
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6
Q

Describe the fovea

A
  • A small central pit
  • Contains closely packed cones
  • Limited convergences: area of greatest visual acuity
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7
Q

Describe phototransduction

A
  • Rods & cones contain chemicals that change shape when exposed to light
  • Photoreceptor excitation is caused by hyperpolarisation
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8
Q

Describe rods

A
  • Outer segment contains rhodopsin
  • When retinal is in a ’11-cis’ configuration, it binds with scotopsin to form rhodopsin
  • When rhodopsin absorbs light it begins to decompose
  • Retinal changes from the cis to trans form
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9
Q

Describe phototransduction in the dark

A
  1. An inward current flows into the outer segment, carried by Na+ ions, through cGMP-gated channels
  2. Current flows out of the cell, through the outflow of K+ ions
  3. Then through non-gated K+ selective channels in the inner segment of the rod
  4. Causing a reduction in membrane potential
  5. Induces the release of glutamate from synaptic end-feet due to Ca2+ influx
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10
Q

Describe phototransduction in the light

A
  1. Rhodopsin decomposition causes breakdown of cGMP
  2. Closes cGMP-gated channels
  3. Induces a hyperpolarisation of membrane
  4. Cell stops releasing glutamate from synaptic end-feet
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11
Q

Describe light adaption

A
  • Sensitivity of the retina needs to be adjusted to detect the dark and light spots on images
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12
Q

List ways of light adaption

A
  • Opening & closing of the pupil
  • Neural adaptation
  • Modulation of amount of light sensitive pigment present
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13
Q

Describe colour vision

A
  • Being able to distinguish different wavelengths of light
  • In humans, it is achieved by our cone photoreceptors:
  • S cones = short wavelength sensitive cones (blue cone)
  • M cones = medium wavelength sensitive cones (green cone)
  • L cones = long wavelength sensitive cones (red cone)
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14
Q

List the retinal interneurons

A
  1. Horizontal Cells
  2. Bipolar Cells
  3. Amacrine Cells
  4. Ganglion Cells
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15
Q

Describe Horizontal Cells

A
  • Laterally interconnecting neurons

- Provide lateral inhibitory feedback

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16
Q

Describe Bipolar Cells

A
  • Transmit signals vertically from rods, cones & horizontal cells to ganglion or amacrine cells for communication to the brain
  • Dendrites from bipolar cells receive from either rods or cones NOT both
17
Q

Describe Amacrine Cells

A
  • Aid in the beginning of visual signal analysis

- About 30 different types

18
Q

Describe Ganglion Cells

A
  • Transmit output signal from retina to brain via optic nerve
  • Only ganglion cells communicate using action potentials
19
Q

List the different types of ganglion cells

A
  1. Midget Ganglion Cells
  2. Parasol Ganglion Cells
  3. Bistratified Ganglion Cells
20
Q

Describe Midget Ganglion Cells (X-Cell)

A
  • Largest population of ganglion cells (80%)
  • Mostly in fovea
  • Involved in fine spatial discrimination & colour perception
21
Q

Describe Parasol Ganglion Cells (W-Cell)

A
  • Make up around 10% of ganglion cell population
  • Synapse with all bipolar cells except midget
  • Involved in spatial discrimination & detection of movement
22
Q

Describe Bistratified Ganglion Cells (Y-Cell)

A
  • Make up around 5% of ganglion cell population

- Involved in perception of yellows and blues

23
Q

Explain Lateral Inhibition

A
  • Horizontal cells connect laterally between rods, cones & bipolar cells
  • Essential for transmitting contrast borders in the visual image
24
Q

Describe On and Off Centre Cells

A
  • Second mechanism for enhanced detection of borders/ edges
  • On-centre cells: excited when stimulated by light in centre, inhibited by light in periphery
  • Off-centre cells: inhibited when light strikes centre, excited by light in their periphery
25
Q

List the visual pathway to the brain

A
  1. Retina
  2. Optic nerves
  3. Optic chiasm
  4. Optic tracts
  5. Lateral geniculate bodies (LGN)
  6. Optic radiations
  7. Visual cortex
26
Q

Explain Lateral Geniculate Nucleus (LGN)

A
  • Located in the thalamus
  • Primary relay centre for visual information from retina to primary visual cortex
  • Consists of two main zones, and one sub-zone:
    1. Parvocellular (layers 3-6)
    2. Magnocellular (layers 1-2)
    3. Koniocellular (sub-layers 1-6)
27
Q

Describe Layers 1 & 2: magnocellular layers

A
  • Large neurons
  • Mainly receive input from parasol ganglion cells
  • Rapid conduct. colour blind, black & white information
28
Q

Describe Layers 3-6: parvocellular layers

A
  • Small to medium sized neurons
  • Mainly receive input from midget ganglion cells
  • Moderate conduct, convey colour, accurate point to point spatial information
29
Q

Describe sub-layers 1-6: Koniocellular sub-layers

A
  • Medium sized neurons
  • Mainly receive input from bistratified ganglion cells
  • Moderate conductance, convey colour (yellow & blue)
30
Q

Define Anopia/Anopsia

A
  • A defect in the visual field
31
Q

Define Hemianopia

A
  • An anopia affecting half of the visual field of one eye
32
Q

Define Quadrantanopia

A
  • An anopia affecting a quarter of the visual field of one eye
33
Q

Define Homonymous

A
  • Same side of both eyes
34
Q

Define Baum’s Loop

A
  • Superior retinal fibres (upper occipital radiation)
35
Q

Define Meyer’s Loop

A
  • Inferior retinal fibres (lower occipital radiation)

Ocular Anatomy and Physiology (10 decks)

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