21.6: NS, Visual pathway Flashcards
Bitemporal hemianopia?
(II ) ( II)
In response to light, what these ganglion cells do?
ON
OFF
ON: depolarise
OFF: hyperpolarise
What are the two types of ganglion cells?
M (parasol): motion
P (midget): colour, acuity
Which ganglion cell is most numerous?
P: 85%
What is the target/termination of most GCs?
What is its role?
Lateral geniculate nucleus (thalamus)
A relay station for vision
Fibres from ___ nerves combine to form the _____ ____.
Fibres from optic nerves combine to form the optic chiasm
Where is the optic chiasm?
Base of the brain, anterior to the pituitary
Which part of the visual field does the R cortex encode?
L visual field (both eyes)
What will a pituitary tumour impinge on? What does this lead to?
Optic chiasm, visual field defect (bitemporal hemianopia)
What are the layers of the LGN?
Which are for M/P?
Which are for L/R?
6 layers
1, 2: Magnocellular layers
3-6: Parvocellular layers
R eye: 2,3,5
L eye: 1,4,6
What is an optic radiation?
Giant white matter tract (neurons from LGN)
Where is central and peripheral vision encoded?
Central: posterior occipital lobe
Peripheral: calcarine fissure
If a lesion is anterior to the chiasm, what happens to vision?
Unilateral vision (one eye defect)
If both eyes are affected, where is the lesion?
If the same side on both eyes is affected where is the lesion?
Chiasm and back
After the chiasm
What have we learned about the neural activity of ganglion cells from blind subjects?
Even without photoreceptors, the ganglion cells respond.
What is the pain pathway for a migraine?
Dura (meninges blood vessels)–> V–>brainstem–>thalamus (posterior nucleus)
What are ipGCs? What do they contain? What do they do to light?
Intrinsically photosensitive GCs. Contain melanopsin (depolarise to light)
What controls pupil:
dilation
constriction
Dilation: dilator pupillae (SNS)
Constriction: sphincter pupillae muscle (PSNS, CNIII)
What is the pathway for pupil responses?
Light–>ipGC–>optical pretectal nucleus (midbrain)–>EW nucleus–>CNIII to opposite eye (constriction)
What drives circadian rhythm? How?
SCN (suprachiasmatic nucleus) in the hypothalamus (ipGCs project here)
What happens with regards to photophobia from a migrane in blind patients (with some and without light perception)
No light perception: NO aura or effect of light
Some light perception: Aura, light exacerbates migrane
