finals vision part 1 & 3

sclera

the white of the eye that provides a tough outer covering that helps the eyeball maintain its shape

cornea

a clear, blood vessel-free extension of the sclera, where the light enters

anterior chamber

the area of the eye located dire behind the cornea, containing aqueous humor that nourishes the cornea and lens

pupil

the opening of the pupil in response to the amount of light present in the environment and is affected by the emotional state due to the autonomic nervous system

iris

it adjusts the opening of the pupil in response to the amount of light present in the environment and is affected by the emotional state due to the autonomic nervous system

lens

helps focus light on the retina in the back of the eye and functions very much like the lens of a camera. it is capable of accommodation, wherein muscles attached to the lens allow us to adjust our focus as we look at objects near us or far away. also, nourished by the aqueous humor of the anterior chamber

vitreous chamber

the major interior chamber of the eye; filled with a jelly-like substance called vitreous humor.

unlike the aqueous humor, which circulates and is constantly renewed, the vitreous humor you have today is the same vitreous humor with which you were born.

retina

the elaborate network of photoreceptors and interneurons at the back of the eye that is responsible for sensing light.

the image that is projected on the retina is upside down and reversed relative to the actual orientation of the object being viewed.

photoreceptors

specialized sensory cell in the retina that responds to light.

optic disk

the area in the retina where blood vessels and the optic nerve exit the eye.

this area does not contain any photoreceptors at all, which gives each eye a blind spot. under normal conditions, we don’t notice these blind spots.

macula

a 6 mm round area in the retina that is not covered by blood vessels and that is specialized for detailed vision.

it is responsible for central vision ( ability to perceive visual stimuli focused on it) as opposed to peripheral vision (ability to perceive visual stimuli that are off to the side while looking straight ahead)

central vision

ability to perceive visual stimuli focused on it

peripheral vision

ability to perceive visual stimuli that are off to the side while looking straight ahead

fovea

a small pit in the macula specialized for detailed vision. it contains only one type of photoreceptor called cones that permits vision in bright light

macula

is the center portion of the retina that produces even sharper vision with its rods and cones

fovea

is the pit inside the macula with only cones, so vision can be at its sharpest

ganglion cell layer

the layer of retinal interneurons farthest from the photoreceptors, which contains ganglion cells and gives rise to the optic nerve

inner plexiform layer

the location in the retina containing axons and dendrites that connect the ganglion, bipolar, and amacrine cells

amacrine cell

a retinal interneuron in the inner nuclear layer that integrates signals across adjacent segments of the retina

inner nuclear layer

the layer of retinal interneurons containing amacrine, bipolar, and horizontal cells

bipolar cell

a cell in the inner nuclear layer of the retina that forms part of the straight pathway between the photoreceptors and the ganglion cells

horizontal cell

a retinal interneuron located in the inner nuclear layer that integrates signals from across the surface of the retina

outer plexiform layer

the retinal layer containing axons and dendrites forming connections between bipolar cells, horizontal cells, and the photoreceptors

photoreceptors

neurons that respond to light

outer nuclear area

the location in the retina containing the cell bodies of the photoreceptors

rod

has a long, cylinder-shaped outer segment; it is responsible for scotopic vision (the ability to see in darkness). rods do not provide any information about color, and they do not produce sharp images. in other words, an object seen at night from a distance of only 20 feet would have the same clarity as an object viewed from a distance of 200 feet at high noon

cone

the outer segment is shorter and more pointed than that of a rod; it is responsible for photopic vision (vision in bright light) that is sensitive to color and provides images with excellent clarity

blue or short-wavelength cones

contain the photopigment cyanolabe, which responds to wavelengths of 419 nm (violet)

green or middle-wavelength cones

contain the chlorolabe that has a peak response of 531 nm (green)

red or long-wavelength cones

contain erythrolabe that peaks at 558 nm yellow

dichromacy

having eyes that contain two different cone photopigments.

became genes for the red and green photopigments appear on the X chromosome, this type of ______ is sex-linked: men are about ten times more likely to be colorblind than women.

the gene for the blue photopigment is located on Chromosome 7 so this case is not sex-linked and appears equally in males and females.

deuteranomaly

is the most common type of red-green color vision deficiency. it makes certain shades of green look more red. this type is mild and doesnt usually get in the way of normal activities

protanomaly

makes certain shades of red look more green and less bright. this type is mild and usually doesn’t get in the way of normal activities

protanopia

is more severe than protanomaly as it means there are no working red cone cells present in the eye. red appears as black, and most shades of green, orange, and yellow all appear as just one shade of yellow

deuteranopia

means there are no working green cone cells present. variations of red appear light brown or dark yellow, and most greens appear as beige

tritanomaly

indicates limited or defective blue cone cells. blue appears greenish and distinguishing yellow or red from pink is impossible

tritanopia

lacking in blue cone cells. blue appears identical to green and yellow is easily mixed up with violet or even dark gray. it also makes colors look less bright

monochromacy

condition occurs when a person has only one type of cone or a complete absence of cones. in either case, the person can’t see color at all

cone monochromacy

an extremely rare condition in which two out of the three cone cell photopigments are defective. to that extent, there is red cone monochromacy, green cone monochromacy, and blue cone monochromacy. since the brain has only one type of working cone cells, it can’t compare signals from different types of colors to distinguish them

rod monochromacy

the rarest and most severe form of color blindness in which there are no functional cone cells with working photopigments. people with __________ can only see black, white, and gray. people experiencing this are photophobic, meaning they are easily overwhelmed in very bright environments

transduction

the process of translating a physical stimulus into electrical signals that can be understood and processed by the nervous system

rhodopsin

the photopigment found in rods, has two parts, opsin and retinal. opsin is a protein chain, whereas retinal is a chemical made from vitamin a

11-cis form

when the retinal is bound with opsin, the resulting molecule of rhodopsin has a tail that bends ______

all-trans form

then, when the light enters the eye, photons are absorbed by rhodopsin molecules, which change the retinal from the 11-cis form to the ______. this change in structure causes the rhodopsin molecule to break apart rapidly

-30mV

the resting potential of a rod outer segment in complete darkness is about _____

neurons ; rods ; cyclic guanosine monophosphate (cGMP)

sodium channels in ____ are typically kept closed when the cells are at rest. however, sodium channels in ____ are kept open by a second messenger, _______ which is constantly produced by the photoreceptor

depolarized ; hyperpolarized

the end result is that photoreceptors are _____ in the dark and ______ in the presence of light

graded potentials

photoreceptors produce _____ rather than action potentials. bright light leads to greater hyperpolarization, whereas dim light leads to less hyperpolarization

glutamate

in terms of neurotransmitters, photoreceptors release the largest amounts of _____ while in the dark

bipolar cells

receive input from photoreceptors and from horizontal cells. in turn, _____ communicate with the amacrine cells in the inner nuclear layer and with ganglion cells

off bipolar cells

depolarize in the dark

on bipolar cells

depolarize in the light

ganglion cells

receive input from bipolar and amacrine cells. the presence of light simply changes the ganglion cells’ spontaneous rate of signaling

off-center ganglion cells

increase firing rate in the dark

on-center ganglion cells

increase firing rate in the light

parvocellular

retinal ganglion cell that is small and responds to high contrast and color

magnocellular

large ganglion cell that responds to all wavelengths regardless of color, subtle differences in contrast, and stimuli that come and go rapidly

koniocellular

a small percentage of ganglion cells that do not fit the criteria for P or M cells exactly and respond to blue and yellow light

sensation ; perception

_____ is the process of obtaining information about the environment and transmitting it to the brain for processing, whereas ______ is the process of interpreting sensory signals sent to the brain

feature detector

a hypothetical neuron that responds to a single feature of the visual stimulus

contrast sensitivity

the ability to perceive sharp and clear outlines of very small objects, or ability to identify minute differences in the shadings and patterns