Flashcards in Visual Pathway Deck (60):
What kind of glutamate receptors can bipolar cells express?
Why are there different types of ganglion cells?
Each type provides info for different stream of vision
What are two types of ganglion cells?
Are M and P ganglion cells ON or OFF ganglion cells?
Each type has ON and OFF type
- M ON
- M OFF
- P ON
- P OFF
Describe M ganglion cells
Large cell bodies
Covers large area of retina
10-15% of ganglion cells
Especially prone to disease
Describe P ganglion cells
Small cell bodies
80% of ganglion cells
What are the targets of ganglion cell axons?
Lateral geniculate nucleus (LGN) in thalams
Pretectum in midbrain
Suprachiasmatic nucleus in hypothalamus
Various other nuclei of thalamus
Why do ganglion cell axons project to the LGN?
Major target of most ganglion cells
Why do ganglion cell axons project to the pretectum?
Why do ganglion cell axons project to the suprachiasmatic nucleus?
Why do ganglion cell axons project to the superior colliculus?
Why do ganglion cell axons project to the nuclei in the thalamus other than the LGN?
What is the optic chiasm?
Fibres from right and left optic nerves combine
How many ganglion fibres cross at the optic chiasm?
Where is the optic chiasm?
Base of brain anterior to pituitary
From which hemifield does the nasal retina receive light information?
From which hemifield does the temporal retina receive light information?
Which fibres cross at the optic chiasm?
Which hemisphere views each hemifield?
Right visual hemifield viewed by left hemisphere
Left visual hemifield viewed by right hemisphere
What part of the visual field does a stroke affect when it's in the visual cortex?
Half of each field in each eye, rather than one entire eye
What is the name of the tract after the optic chiasm?
Where do ganglion cell axons in the optic tract synapse?
How many neurons are there in the visual pathway?
Why is the anatomical position of the optic chiasm relevant to pathology?
Pituitary gland just below
Condition affecting it can affect chiasm; eg: in pituitary macroadenoma
What is the classic presentation of a person's visual field when they have a pituitary macroadenoma?
Which hemifields are affected in bitemporal hemianopia?
Where do second order neurons in the visual pathway arise from?
How is information in the LGN segregated?
By eye and ganglion cell type
How many layers are there in the LGN?
What are the types of cells in the LGN?
Where do M ganglion cells synapse?
Magnocellular layers: 1 and 2
Where do P ganglion cells synapse?
Parvocellular layers: 3-6
Which layers receive input from the right eye?
2, 3, 5
Which layers receive input from the left eye?
1, 4, 6
Where do LGN neurons project to?
Primary visual cortex (V1)
What is the Broddman's area of V1?
Where in the brain is the primary visual cortex?
Occipital lobe around calcarine fissure
- On medial aspect
- Upper and lower banks around fissure
How is information organised in the primary visual cortex?
Retinotopic organisation = neighbouring cells within retina project to neighbouring cells in LGN and visual cortex
Which part of the visual cortex receives information from the macula?
Most posterior part = macular cortex
Which part of the visual cortex receives information from the peripheral retina?
What visual field is affected when there's a lesion in the right optic nerve?
Right eye visual field
What visual field is affected when there's a lesion at the optic chiasm?
What visual field is affected when there's a lesion in the right optic tract?
Left visual hemifields
What visual field is affected when there's a lesion in the right optic radiation?
Upper left quadrant of visual fields of both eyes
How can the visual field of the macula be spared when there's a lesion in the right visual cortex?
Only happens with vascular event
Macular cortex supplied by different blood supply than rest of occipital lobe
If infarct in vessel supplying rest of occipital lobe, then macular vision spared
What is the tract from the LGN to the primary visual cortex called?
What are intrinsically photosensitive ganglion cells?
Small population of ganglion cells containing visual pigment = melanopsin
Light activation of melanopsin > intrinsically photosensitive ganglion cells depolarise
What are the functions of intrinsically photosensitive ganglion cells?
General info about light levels
What is light allodynia?
Photophobia associated with
- Ocular injury
What do pupil responses depend on?
Being able to detect light
What are the two muscles of the iris?
Where is one projection of melanopsin ganglion cells?
Optical pretectal nucleus (OPN)
Where do ganglion fibres heading to the OPN diverge from the visual pathway?
After optic chiasm
Where do neurons from the OPN synapse with to control pupil responses?
Which side of the brain does the OPN send fibres to in order to provide information for pupil motor responses?
At what age do babies start to develop circadian rhythms?
Where do intrinsically photosensitive ganglion cells project to in order to provide information for the circadian rhythm?
Suprachiasmatic nucleus (SCN) in hypothalamus
What is the effect of light in migraines?
What is the pain pathway for migraines?
Thought to be due to nerves signalling from dura
Pain from dura carried by trigeminal nerve
Dura > trigeminal nerve > brainstem > posterior nucleus of thalamus