visual system Flashcards
the eye is a fluid filled sphere enclosed by what 3 layers of tissue (what is their order from outermost to innermost)
sclera (outermost), choroid (intermediate) and retina (innermost)
what are the 2 fluid compartments of the eye
aqueous humor and vitreous humor
describe aqueous humor (where, consistency, function)
in ant chamber
watery liquid
supplies nutrients to surrounding structures
describe vitreous humor (where, consistency, function)
fills space btw back of lens and retina
thick gelatinous substance
maintains shape of eye and supplies nutrients to surrounding structure
what is the sclera
white fibrous tissue forming the outermost layer of the eye
what does the sclera become in front of the eye
cornea
what is the cornea
transparent tissue that separates and protects ere from external environment and allows light rays into the eye
what is the choroid
capillary bed that nourishes retinal cells
whats the ciliary body and what two parts does it have to it
a ring of tissues that encircles the lens and consists of a muscular (ciliary m.) and vascular part (ciliary processes)
whats the function of the ciliary muscle and what connects it to the lens
controls the shape of lens
Zonule fibers
whats the function of ciliary processes
produces aqueous humor in ant chamber
whats the iris, what does it contain and whats their function
colored portion of the eye seen thru cornea
contains 2 sets of m. that contract and adjust size of pupil
what does the lens do
it refracts light rays coming into eye and generates a focused image on the surface of the retina
what does accommodation of the lens mean and what part of the eye does these accommodations
dynamic changes in refractive power of the lens to form a shape image on the retina
done by contraction of ciliary m.
what accommodation of the lens is done for distant vision
lens becomes thin and flat, less refractive power
what accommodation of the lens is done for near vision
lens becomes thick and round, more refraxctive power
where is the image focused in emmetropia
right on the retina (normal eye)
describe myopia (how does the lens accommodate, where is the image, hard to see what, corrected by what)
lens doesn’t accommodate enough
image is in front of retina
hard to see distant objects
corrected by converging (convex) glasses
describe hyperopia (how does the lens accommodate, where is the image, hard to see what, corrected by what)
lens over accommodates
image is focused beyond the retina
hard to see nearby objects
corrected by diverging (concave) glasses
the retina is considered to be part of what
the nervous system
what is the retina’s function
it contains neurons that are sensitive to light, and convert visual info to electrical signals and transmit it to the brain
what are the 2 photoreceptor neurons
rods and cones
describe rods (shape, number, location in retina, luminosity level, vision accuracy, photosensitive pigments, type of cell, color vision)
shape: rod-shaped (rectangular head)
number: 120 millions
location in retina: periphery
luminosity level: dim light (highly sensitive to light)-night vision
vision accuracy: low resolution
photosensitive pigments: rhodopsin (found in carrots)
type of cell: 1: monochromic (absorb white color)
color vision: no
describe cones (shape, number, location in retina, luminosity level, vision accuracy, photosensitive pigments, type of cell, color vision)
shape: cone-shaped (triangular head)
number: 8 millions
location in retina: center (fovea)
luminosity level: bright light (low sensitivity to light)- day vision
vision accuracy: high resolution
photosensitive pigments: iodopsin, porphyropsin, cyanopsin
type of cell: 3 types; S-cones (blue), M-cones (green), L-cones (red)
color vision: yes
what are the 5 classes of neurons of the retina
photosensitive
bipolar cells
ganglion cells
horizontal cells
amacrine cells
what forms the optic nerve
axons of the ganglion cells
what cells regulate the activity of photosensitive neurons
horizontal cells
what cells are the lateral communication between neurons
amacrine cells
what is the electrical activity of photosensitive and retinal neurons for dark light
dark light –> cone cell depolarized –> bipolar cell hyperpolarized (active inhibition) –> ganglion cell hyperpolarized (passive inhibition) –> no info transmitted to the brain
what is the electrical activity of photosensitive and retinal neurons for light light
light –> cone cell hyperpolarized –> bipolar cell depolarized –> ganglion cell depolarized –> info transmitted to the brain
what are the 2 classes of ganglion cells (what are they active and silent to)
on-center cells: active to light spot in center and silent to dark spot in center
off-center cells: silent to light spot in center and active to dark spot in center
what other type of cell as on and off-center cells
bipolar cells
the activity of on-center and off-center ganglion cells are controlled by what and what behavior do these interractions determine
multiple interractions btw photosensitive cells, bipolar cells and horizontal cells
center-surround behavior
what cells regulate the amount of transmitter that the photosensitive cells release onto bipolar cell dendrites
horizontal cells
how is an image projected on the retina
inverted top to bottom and revered R to L
the visual field is divided into what
2 hemifields: R and L hemi field
the R visual hemi-field is seen by what type of retina
right nasal and left temporal retinas
the L visual hemi-field is seen by what type of retina
left nasal and right temporal retinas
what is the name of when visual fields of both eyes overlap in the central portion of visual field
binocular visual field
what % of optic n. fibers cross at the optic chiasm and what % stay on the same side
60% contralateral
40% ipsilateral
what retina fibers project to contralateral side
fibers fron nasal retina
what retina fibers project to ipsilateral side
fibers fron temporal retina
after the optic hciasm, what do the optic fibers form
optic tract
where do the majority of the optic fibers terminate
Lateral geniculate body in the thalamus
what do neurons from the LGB form and where do they terminate
optic radiation and they terminate in the striate cortex
where do axons of the ganglion cells also project in the midbrain
hypothalamus, pretectum, sup colliculus
function of hypothalamus
reg of circadian rhythm (biological clock)
function of pretectum
control of pupillary light reflex
function of sup colliculus
orienting the mvts of head and eyes
what are the other names for visual cortex
striate cortex, primary visual cortex, V1, Brodmann’s area 17
what does the visual cortex process (give examples)
basic sensory info sent by retina
examples: place back inverted image to og position, binocular vision, 3D image, …
what representation in the visual cortex does the central region (macula, fovea) of the retina have
a large representation
what is called the 6 cellular layers in the striate cortex
cytoarchitecture
describe binocular vision (combining inputs from both eyes)
-lat geniculate nucleus receives input from both eyes (monocular)
-LGN input remains segregated in layer 4 of the striate cortex (ocular dominance columns) (monocular)
-layer 4 send their outputs to other cortical layers (binocular vision)
what is involved in complex visual pathways
extrastriate cortex
what are the 2 complex visual pathways
dorsal (where) path and ventral (what) path
what are each pathway responsible for and where do they project to
dorsal: project to parietal lobe, and responsible of spatial aspect of vision (analysis of motion)
ventral: projects to temporal lobe responsible for object recognition
consequence of damage at Left lat and med visual field before optic chiasm
Left is gone R is intact
consequence of damage at Left med visual field before optic chiasm
R and L lat is intact , L med is gone
consequence of damage at L and R visual field at optic chiasm
L med and R med are intact, L lat and R lat are gone
consequence of damage at visual field at med optic tract before geniculate nucleus
L lat and R med are intact, R lat and L med are gone
consequence of damage at visual field at med optic tract after geniculate nucleus
L lat and R med are intact, R lat and L med are gone
