Vision Flashcards
What are the two types of bipolar cells and which receptor is associated with which one?
ON and OFF bipolar cells
- ON bipolar cells have a metabotropic glutamate receptor that hyperpolarises when glutamate binds
- OFF bipolar cells have an ionotropic glutamate receptor that depolarises when glutamate binds
What do horizontal cells release and how do they work?
Stimulated by photoreceptors and release GABA (inhibiting) onto other photoreceptors to create the centre surround
What are M ganglion cells?
Parasol ganglion cells: motion
- have a large cell body
- encode where in the visual field the image is, and if it is moving
- not very many of them
What are P ganglion cells?
Midget ganglion cells: colour vision, visual acuity
- small
- take info about what you’re seeing
What is the optic chiasm?
Fibres from the right and left optic nerves combine to form the optic chiasm which lies at the base of the brain, anterior to the pituitary in the sphenoid bone
- nasal fibres from each nerve cross at the optic chiasm
How are the visual fields viewed by the hemispheres?
Left visual hemifield is viewed by the right hemisphere
Right visual hemifield is viewed by the left hemisphere
What visual defect can be caused by a pituitary adenoma or some other pathology at the optic chiasm?
Bitemporal hemianopia
What visual deficit will you get if a lesion is anterior to the optic chiasm?
Unilateral - either eye, could be the retina or the optic nerve
What visual deficit will be caused be a lesion posterior to the chiasm?
Bilateral and on the same side
What is the Lateral Geniculate Nucleus?
Relay station in the thalamus for everything to do with vision
- there is NO mixing of information from each eye at the LGN
- there are 6 layers containing two types of cell
- layers 1, 2 are magnocellular layers, layers 3-6 are parvocellular layers
- segregation of inputs by eye also happens here –> layers 2, 3, 5 for the right eye and 1, 4, 6 for the left eye
What is the mapping of the visual cortex?
Each half of the visual field is represented on the contralateral visual cortex
- macular cortex is as far back in the occipital lobe that you can go (central)
- peripheral is further along the calcarine fissure
What are intrinsically photosensitive ganglion cells?
They can respond to light because the contain melanopsin (similar to rhodopsin)
- light activation of melanopsin leads to depolarisation of ipGCs
How does the pupil response work?
Shine a light into one eye –> optic nerve –> pretectal nucleus –> EWN on BOTH sides –> CNIII to ciliary ganglion (PS) –> pupils constrict
What is the function of ipGCs in circadian rhythm?
Project to the suprachiasmatic nucleus of the hypothalamus
- controls the light activation of our body clock
What is the function of ipGCs in photophobia?
ipGCs project to posterior thalamic nucleus that are light sensitive, linked to migraine pain because this is going to the same area
