What CN does vision
CN II- optic nerve
Why is CNII NOT a peripheral nerve?
retinal structure from diencephalon development
myelinated neurons with oligodendycytes-CNS
What is the pathway of light traveling into the eye?
Iris through lens to retina- focused on fovea to optic nerve
What does the pupillary constrictor muscle do?
controls amount of light entering the eye via controlling the iris
- parasympathetic constricts
- synpathetic relaxes
What do ciliary muscles do?
adjusts lens thickness to help bend light to focal point (fovea)
- visual accomodation
- paraysmp: thickens
- sympathetic relaxes
What is the retina? what’s in it?
has visual receptors lining the walls of the eye
- macula on posterior wall= increase density
- fovea in macula= highest density of cones
What is the optic disk? what’s in it?
blind spot
- axons from retina and vasculature exit through here
- vascular from internal carotid-opthalamic vessels
What makes up the fovea?
5 types of neurons
- mainly photoreceptors= rods and cones
- retinal ganglia cells
Everything flipped upside down!!
What are rods?
photoreceptor in fovea
- ALL wavelengths visible light
- dense around macula
- detects light levels and motion– course vision
What are cones?
photreceptor in fovea
- 3 types of pigements to transduce color wavelenths: red, green, blue
- most dense around fovea where macula has greatest visual acquity
What are retinal ganglia?
output neurons- 1CB of visual pathway
- axons collect at optic disk and once exit eye all travel as CNII
- unmeylinated axons until exit disk-> myelinated with oligodend
What are pigment epitheliums? what are the 3 types?
melanin that absorbs light to decrease scatter
- opesins: photo pigment for color
- rodespin: light/dark
- melanopsin: special ganglia with melanin
What are the 4 possible pathways of visual perception?
- Primary pathway-> V1
- occipital pole - Suprachiasm nucleus of hypothal
- diurnal clock
- light/dark
- melanopsin - Pretectal nuclei (midbrain)
- pupil constrictor/thicken lens
- parasympathetic reflexes - Superior colliculus (midbrain)
- eye movements relative to environment
What is the 1neron characteristic of the Primary Visual pathway?
axons off of photoreceptors
- collect/sort 3 regions of projections
- all axons travel in ipsilateral optic nerve
- enter chiasm: vulnerable to pituitary tumor damage
Nasal: 60% decussate in chiasm-> contrlateral optic tract
Temporal: 40% stay ipsilateral-> ipsilateral optic tract
Tracts-> LGN -> internal capsule -> optic radiations -> VI
What is the BA number of V1
BA 17
What are the layers of the LGN
4 parvocellar layers: show color
2 magnocellar layers: percieve motion
What is the striate cortex?
superior and inferior banks by calcacrine sulcus
Inferior visual field goes up through parietal to SUP bank
Superior visual field goes down through temporal to INF bank
-some bend around inferior horn of lateral ventricles= Meyers loop
What is the monocular visual field?
Vision of one eye
-seperate into 4 quadrants: superior, inferior, nasal, and temporal
TEMP CRESCENTS 930 deg) project to NASAL retina
What is the binocular visual field?
Detected by both eyes
-majority of visual field except small monocular temporal crescents
MOST (90 deg) projects to BILAT TEMPORAL retina
What do the extraocular muscles do in relationship to convergence?
control eye alignment- focul point on fovea
-converge to fovea to get optimal visual acuity
How does the light refract through lens and in brain?
Inverted through lens onto retina
- inferior field on top
- superior field on bottom
L and right fields are flipped
-temporal visual field of L eye projects to nasal retina of left eye
Where do the R visual fields project in the brain?
LEFT V1
What does damage to the L eye/optic nerve result in?
Ipsilateral blindness
- can’t see from L eye
- monocular field deficit
What does damage to the L optic chiasm do?
Bitemporal meianopia
- impaired peripheral vision bilaterall
- affects nasal retina axons at decussations
