Lecture 5: Vision Flashcards
What are the types of cells found in the retina? If there are different types of one cell what are they? What are their functions?
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Photoreceptors - detect light
- rods (black and white for night vision)
- cones (colour day vision)
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Bipolar cells
- connects photoreceptors to ganglion cells
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Ganglion cells - projection cells to the optic nerve
- Magnocellular - motion
- Parvocellular - colour
Other cells:
- Amacrine cells
- Horizontal cells
- Pigment epithelial cells (most superficial layer)
- eats up shedded discs of photoreceptors
What are pigment epithelial cells?
They are found in the most superficial layer of the retina and are phagocytes that eat up shedded discs of photoreceptors
What are the two types of ganglion cells?
- Magnocellular (sends information about motion)
- Parvocellular (sends information about colour)
What is the blindspot?
The optic disc where axons form the optic nerve.
What happens to vision with a prechiasmatic lesion?
Prechiasmatic lesions result in vision loss in one eye.
What happens to vision after a postchiasmatic lesion?
You may have vision loss in both eyes
What is the fovea centralis?
A part of the temporal retina where light hits photoreceptors flush
What is the macula lutea?
A ‘mountain’ of ganglion cells surrounding the fovea centralis - located in the temporal retina.
Where in the retina has peak visual acuity?
The fovea centralis and macula lutea: This area has the greatest density of ganglion cells and photoreceptors. You may have one photoreceptor talking to one ganglion cell, whereas in the periphery 1 ganglion cell may be recieving input from 1000s of photoreceptors.
Which part of the retina crosses to the other side?
Nasal retina crosses projects to the contralateral lateral geniculate nucleus via the optic chiasm.
Temporal retina projects to the ipsilateral lateral geniculate neucleus.
What is the function of the lateral geniculate nucleus
The LGN is like the butler - that reorganises everything for the visual cortex. It has three main jobs
- Streams - what function? Magnocellular or parvocellular?
- Where are you from? (topography) are you from central retina or peripheral retina
- laterality - which eye are you from? contralateral or ipsilateral?
How many layers are there of the lateral geniculate nucleus? Describe the significance of this?
There are 6 layers (4 parvocellular - located dorsally and 2 magnocellular - located most ventrally)
- Remember the right LGN recieves input from left visual field
- Each layer gets precise retinotopic input from just one eye.
- Layer 1 - magnocellular input from contralateral eye
- Layer 2 - magnocellular input from ipsilateral eye
- Layer 3 + 5 - parvocellular input from ipsilateral eye
- Layer 4 + 6 - parvocellular input from contralateral eye
An object in the visual field will activate a particular column in the LGN, when it moves the column of activation moves.
Describe the non-image forming pathways (unconscious vision)
Retinal ganglion cells project directly to:
- Suprachiasmatic nucleus - which is involved in circadian rhythms. Second order neurons project to the pineal gland which releases melatonin. (note: the retina also releases melatonin)
- Pretectum - involved in the pupillary reflex, projects to the Edinger-Westphal nucleus which projects to both eyes via occulomotor nerves
- Superior colliculus - involved in visual reflexes (such as attention - tracking an object and avoidance - visomotor reflex that turns neck and eye away from an item) and projects to the pulvinar which is involved in higher order attention and integration of sight, touch and sound). The pulvinar projects to secondary visual cortices (V2-V5).
What is the function of V2 and V3?
Orientation of objects
