Visual Pathways Flashcards
how many rods are there
130 million
what type of vision do rods provide
- black and white
- dim
- peripheral
three components of rods
- inner
- outer (700 discs, contains rhadapsin)
- rod fibre (nucleus)
what does rhadapsin do
inhibits glutamate which is continuously secreted in darkness
what type of vision do cones provide
- colour
- bright light
how do cones work
3 types - each contain a different pigment to allow for the absorption of red, green and blue light
2 components of cones
- inner
- outer (pigment-bearing discs)
midget cells
- small dendritic arbors
- small slow moving nuclei
- not sensitive to low contrast
- colour
parasol cells
- large dendritic arbors
- large fast moving nuclei
- not sensitive to low contrast
- colour
name 3 association neurons
- amacrine cells
- horizontal cells
- interplexiform cells
amacrine cells function
inhibitory and exitatory
horizontal cells function
inhibitory
interplexiform cells functon
feedback between amacrine and horizontal cells
muller glial cells function
support
pathway to visual cortex
optic nerve → optic chiasm (hypothalamus) - visual fields cross → lateral geniculate nucleus of the thalamus
name the four portions of the optic nerve
- intraocular portion
- intraorbital portion
- intracanalicular portion
- intracranial portion
where is the optic tract and chiasm found
superior to the sella turcica and therefore the pituitary gland which it contains
what is the optic tract and chiasm susceptible to
secondary pituitary disorders
what is the pulvinar nucleus
Most fibres travel from the chiasm after splitting to lateral geniculate nucleus but 10% travel to superior colliculus and pulvinar nucleus and from here to the primary visual cortex
where is the pulvinar nucleus found
- thalamus - largest thalamic nucleus (25% of thalamus size)
- medial and dorsal to lateral geniculate nucleus
what is the lateral geniculate nucleus
6 layered structure:
4 parvocellular layers
2 magnocellular layers
what do the parvocellular layers receive input from
lateral geniculate nucleus
midget ganglion cells
what do the magnocellular layers recive input from
parasol cells
what are optic radiations
geniculocalcarine fibres
optic radations pathways
- exit dorsally from the lateral geniculate nucleus, then spread into two major bundles (superior and inferior)
- The dorsal and central bundles travel in parietal lobe to the visual cortex
- The ventral group (meyer’s loop) of fibres curves in an anteroinferior direction into the anterior pole of the temporal lobe
information processed in primary visual cortex
- static vs moving objects
- pattern recognition
where are the second visual cortices found
- occipital lobe
- parietal lobe
- temporal lobe
information processes in secondary visual cortices
- object recognition
- colour perception
- depth
- motion
two types of visual defects due to interruptions of the pathway at the retina
- retinal deachment
- colour vision deficiency
explain retinal detachment
- due to blow to the eye or spontaneously
- fluid accumulation
- can lead to blindness
explain colour vision deficiency
- dichromatic vision: one opsin not produced
- monochromatic vision: 2 opsins not produced
four visual defects due to interruptions of the pathway at the optic pathway
- monocular blindness
- bitemporal hemianopia
- homonymous hemianopia
- lesions of primary visual cortex
explain monocular blindness
- lesion at optic nerve
- stroke (ophthalmic artery)
- migraine (transient)
- multiple sclerosis (bilateral)
explaim bitemporal hemianopia
- optic nerve compresson
- pituitary tumour
- information from temporal visual fields falls on nasal retina
- vision is missing in outer half of both left and right visual field
homonymous hemianopia
- posterior cerebral artery stroke
- lesion in optic chiasm
- vertical midline loss
lesiond of primary visual cortex
- scotoma
- hole in visual field
