15 Flashcards
(15 cards)
Explain the functions of cornea, iris, lens, and retina
a. Cornea – directs light into the eye and focuses it, light bending, 80% refraction
b. Iris – controls the amount of light entering, colored part, eye color ring of tissue that
lays on top of lens
c. Lens – focuses light on retina, 20% refraction, can change shape depending on distance -
accomodation - close by lens Is rounder, far away is flatter
d. Retina – converts light into electrical signals for brain to process, receptors that detect
light coming in from outside
Be able to point out the above structures and the sclera and conjunctiva.
b. Sclera - white part of eye
c. Conjunctiva - is a tissue that lines the inside of the eyelids and covers the sclera (the
white of the eye).
Which structures refract light, in what proportions to they take care of the refraction?
a. Cornea – 80%
b. Lens – 20%
Cornea: the transparent part at the front of the eye that refracts light entering the eye onto the lens.
Lens: a transparent structure behind the iris that refracts incoming light and focuses it onto the retina.e
Explain what the fovea and the blind spot on the retina are. How are they related to sensitivity of
these areas? What is the macula?
b. Fovea – highest density of receptors (cones), responsible for sharp central vision
necessary for activities where visual detail is of primary importance
i. More receptors = more sensitivity
c. Blind spot (optic nerve) – no cells to detect light on the optic disc, a part of the field of
vision is not perceived, only axons. The brain interpolates the blind spot based on surrounding detail and information from the other eye, so the blind spot is not normally perceived.
d. Rods - light/dark, more rods than cones, 120 * 106, less distribution
e. Cones - taste, sensation, perception (colors), 6 * 106, not evenly distributed
f. Macula – processes what you see directly in front of you (your central vision
What are the three cell layers of retina, and how does the light travel to get to the receptor layer?
Why does this appear counterintuitive?
a. 3 cell layers: Ganglion Cell Layer, Bipolar Cell Layer, Photoreceptor Cell Layer
b.
c. actual receptors are all the way in the back- the light has to get through a layer of axons,
through a layer of the cell bodies that go with the axons, then through bipolar cells,
before reaching the photoreceptors
What is the main pathway for vision called, what is its course? What % of fibers go this way?
a. Geniculostriate pathway - 80-90% of fibers go this way
i. Most important axons convey information to lateral geniculate nucleus (LGN) in
thalamus (brain’s sensory relay station) Information then relayed (via optic
radiations) to striate cortex & V1 (in the occipital lobe at back of brain)
ii. then sent to higher cortical areas for further processing
What is the tectopulvinar pathway and what is its course?
a. 10% of fibers go this way phylogenetically (evolution of a group of species)
b. older eye to superior colliculus to pulvinar in thalamus then to visual areas in temporal
and parietal lobes
What are the optic nerve, optic chiasm, optic tract, LGN, optic radiation, striate cortex, V1?
a. Optic nerve – carrying signals from the eye
b. Optic chiasm – crossover point for optic fibers, results in contralateral projections of information from nasal ganglion cells
c. Optic tract – fundamental visual sensation, carrying signals to the LGN
d. LGN – axons convey information to the lateral geniculate nucleus (LGN) in the thalamus,
relaying signals to the optic radiation
e. Optic radiation – once in thalamus, information is relayed to the striate cortex
f. Striate cortex – receives and processes visual information from the eyes (V1)
g. V1 – Pattern perception, depth perception, color vision called the Primary Visual Cortex
& BA 17
Which parts of the thalamus take part in the geniculostriate pathway and which in the
tectopulvinar pathway?
a. geniculostriate pathway – the lateral geniculate nucleus in the thalamus
i. geniculate (lateral geniculate nucleus) –(via optic radiations to)— striate
pathway (striate cortex, also known as V1, primary visual cortex, BA17) b. tectopulvinar pathway – the pulvinar in the thalamus
i. tecto (tectum) — pulvinar (pulvinar) pathway
1. tectopulvinar pathway is the pathway that goes from the eye to the
superior colliculus (in the tectum/midbrain/mesencephalon) to the pulvinar in the thalamus and finally to areas in the temporal lobe and parietal lobe.
What is the visual field? Explain the overlap between the visual fields of the R and L eyes.
a. Visual field – all of the points of the physical environment that can be perceived by a stable eye at a given moment
b. The visual fields of both eyes overlap in the central portion of each visual hemi field resulting in binocular vision
i. The Nasal hemifield – light from outside
ii. The Temporal hemifield – light from middle
Explain which fibers from the two “hemifields” or “hemiretinas” or halves of the retina go
where before/after the optic chiasm. Which hemifield is nasal and which is temporal?
a. {T/N} {N/T}
i. Information from one side of the visual field, processed by the opposite
hemisphere
ii. Nasal ganglion cells – send axons to contralateral (opposite) LGN, crossing over
at optic chiasm
iii. Temporal ganglion cells is ipsilateral (same side)
b. Nasal and temporal hemi-retinas
i. Nasal gets light from periphery of visual field - near nose
ii. Temporal gets light from overlap of visual field - near temples
c. Right visual field - processed on left side of brain
d. Left visual field - outside falls on left nasal hemiretina, inside fall on temporal hemiretina
on right side - goes to optic chiasm does not cross - goes to LGN info from left CROSSES and goes to right LGN
i. Right nasal hemiretina CROSSES going to left LGN
ii. Temporal hemiretina on left does not cross
What do “ipsilateral” and “contralateral” mean?
a. Ipsilateral – same side, temporal
b. Contralateral – crosses to opposite side, nasal
What are the striate, extrastriate, primary, secondary, tertiary visual cortices?
Striate cortex/Primary Cortex: Each point on the retina is represented by a point on the Striate cortex corresponding to a receptor cell (Retinotopic representation)
Secondary ctx/extrastriate occipital cortex: Depth Perception
Tertiary ctx: Inferior temporal and posterior parietal ctx (and STS): Color/motion Depth.
What are the dorsal & ventral visual streams?
After visual info is processed in V1 → V2, it splits into two major pathways known as the dorsal and ventral streams, each handling different aspects of visual perception.
i. dorsal -occipital cortex to posterior parietal cortex(vision for action)
ii. ventral - occipital to inferior temporal cortex (vision for identification)
What is the function of ventral & dorsal streams? Which one is ‘where/vision for action’ and which one is ‘what’ or ‘vision for identification”?
a. Vision for action - where - dorsal
i. visually guided reaching and grasping based on the moment-to-moment analysis b. Vision for identification - what - ventral
i. recognition and discrimination of visual shapes and objects
