Sight (vision) Flashcards
Conjunctiva
thin layer of cells that lines the inside of your eyelids from the eye.
Cornea
transparent thick sheet of fibrous tissue, anterior 1/6th; starts to bends light,
first part of eye light hits.
Anterior chamber:
space filled with aqueous humour, which provides pressure to maintain shape of eyeball; allows nutrients and minerals to supply cells of cornea/iris.
Pupil:
the opening in the middle of the iris. The size of the pupil can get bigger/smaller based on the iris relaxing/contracting respectively. The pupil modulates the amount of light able to enter the eyeball.
Iris:
Gives the eye color. The muscle that constricts/relaxes to change the size of the pupil.
Lens
bends the light so it goes to back of eyeball – focuses light specifically on the fovea of the retina. Adjust how much it bends the light by changing its shape, using the suspensory ligaments.
Suspensory ligaments:
attached to a ciliary muscle. These two things together form the ciliary body, what secrets the aqueous humor.
Posterior chamber:
area behind the iris to the back of lens; also filled with aqueous humor.
Vitreous chamber:
filled with vitreous humour, a jelly-like substance to provide pressure to eyeball and gives nutrients to inside of eyeball.
Retina:
inside, back area filled with photoreceptors, where the ray of light is converted from a physical waveform to a electrochemical impulse that the brain can interpret.
Macula:
special part of retina rich in cones, but there are also rods.
Fovea
special part of macula. Completely covered in cones, no rods.
*Rest of the retina is covered in primarily rods
Cones:
Detect color and discern high level of detail in what you are observing. Cone
shaped.
Rods:
Detect light. Rod shaped.
Choroid
pigmented black in humans, is a network of blood vessels that helps nourish
the retina. It black all light is absorbed. Some animals have a different colored choroid
which gives them better night vision.
Sclera –
Usually absorbs by the time the light gets to this. The whites of the eye, thick
fibrous tissue that covers posterior 5/6th of eyeball (cornea covers the anterior 1/6). Attachment point for muscles. Extra layer of protection and structure of eyeball. Lined with the conjunctiva.
Transmission
is the electrical activation of one neuron by another neuron.
Perception
is conscious sensory experience of neural processing.
Processing
is the neural transformation of multiple neural signals into a perception.
Transduction
occurs whenever energy is transformed from one form to another; in this
case, light energy is transformed to electrical energy by rods and cones.
Sensation
requires a physical stimulus to be converted into a neural impulse.
In the case of the eye, light is being converted to a
neural impulse by a photoreceptor
What is light?
Light is an electromagnetic wave.
Visible light
Violet (400nm) – Red (700nm). Highest to lowest wavelength: ROYGBV
3 types of cones
red, green and blue
There are 120 million rods, for night vision Light comes in, goes through pupil, and hits rod. Normally rod is turned __, but when light hits turns __
on
off
Bipolar cells
found in the rentina
these cells send visual signals from rods and cones to the ganglion cells
Phototransduction cascade: what happens when light hits rod/cone
1) Light hits rods (which causes rod turns off)
2) a bipolar cell (turns on)
3) retinal ganglion cell (turns on)
4) goes into optic nerve
5) enters BRAIN.
trichromatic theory of color vision
theory states that you have cones that are receptive to 3 colours (R,G,B) these three colors are. mixed together and you precieve colour
Problem with the trichromatic theory of color vision
although out eyes can miz red and yellow to make orange, we can seem to mix red and green or blue and yellow
what theory explain the problem with the trichromatic theory of color
opponent process theory of color vision
what is the opponent process theory of color vision
you have cones that perceive 4 colour, R,G,B,Y
red and green oppose each other
blue and yellow oppose each other
black and white sensitive cones oppose each other
between the opposing color only one colour can be dominate at a time
The Phototransduction Cascade (PTC)
makes the brain recognize that there is light entering the eyeball. The process of making the light -> neural impulse by turning off a rod. The neural impulse can turn on other cells and eventually be processed by the brain.
rods are normally on or off?
on
what happens when light hits a rod turns on or off
off
steps of The Phototransduction Cascade
Phototransduction cascade is the act of turning the rod cell OFF which signals to the brain that light is entering the eye.
Phototransduction cascade goes like this:
In the absence of a light rod is turned ON.
Rods contain rhodopsin (a GPCR) which contains 11 cis retinals.
when the light hit, comes through the pupil, and hit the retinal, it rod, some of the light hits the rhodopsin (which contains the retina) and causes it to change conformation from bent to straight (11 trans retinal)
when the retinal changes shape, rhodopsin changes shape this begins the cascade
a molecule called transducin (three parts alpha, beta, and gamma) is attached to the rhodopsin
when the rhodopsin changes shape the transducin breaks from the rhodopsin and the alpha subunit binds to another disk protein called phosphodiesterase (PDE)
PDE takes cGMP and converts it to GMP
lots of Na+ channels on the rods allow Na+ ions to come in
cGMP bound to Na+ channel keeps the channel open and hence “ON”,
as cGMP concentration decreases, the na+ channel close and the cell turns OFF
when Na+ channels become unbound of cGMP, less na+ enters the cell the cell hyperpolarization and turns OFF
Next, bipolar cells (two variants: ON CENTER and OFF CENTER).
* When light hits ROD, turned off –> ON CENTER bipolar cells active, OFF CENTER bipolar cells inactive.
* When ON CENTER bipolar cells are turned on, this activates ON CENTER retinal ganglion cell, which sends a signal to optic nerve to brain.
Photopic vision occurs
at levels of high light levels.
Mesopic vision occurs at
dawn or dusk and involves both rods and cones.
Scotopic vision occurs
at levels of very low light.
A photoreceptor
is a specialized nerve that can take light and convert to neural impulse.
Inside rods are
optic discs, which are large membrane-bound structures – thousands of
them. In the membrane of each optic disc are proteins that fire APs to the brain
Cones are also specialized
nerves with same internal structure as rod.
Rods contain
rhodopsin
Cons Contain
photopsin.
If light hits a rhodopsin, will trigger the
phototransduction cascade. Same process
happens in a cone.
Differences between rods and cones:
MORE RODS THAN CONES
Cones are concentrated in the fovea
Rods are 1000x more sensitive to light than cones.
Cones detect color primarily but also some light (three types : 60% Red, 30%
Green, 10% Blue)
Rods have slow recovery time vs. cones have fast recovery time
blind spot
Where optic nerve connects to retina, blind spot – no cones or rods.
Rods are found mostly
periphery.
Cones are found primarily
Cones are found primarily in the fovea, and few dispersed through the rest of eye.
At the fovea (dimple in retina) light hits cons directly beacuse ?
there no axons in way of light so get higher resolution.
At the periphery, less light gets to the rods. why?
At the periphery - light has to go through bundle of axons and some energy lost.
All right visual field goes
left side of brain;
vise versa
light travel from the left side visual field?
Ray of light from the left visual field hits the NASAL side of the left eye and hits the TEMPORAL side of the right eye
Vice Versa for light from the right visual field. Ray of light from the right visual field hits the NASAL side of the right eye and hits the TEMPORAL side of the left eye
Optic nerves
from each eye networks the electrical signal to the brain and converge from each eye at the optic chiasm and then break off and dig deeper into the brain
Feature Detection:
When looking at an object, you need to break it down into its component features to make sense of what you are looking at. There are 3 things to consider when looking at any object: color, form, and motion.
What detects form/shape?
Parvocellular pathway: good at spatial resolution (boundaries and shape—high levels of details), and color. But poor temporal (can’t detect motion—only stationary.)
Cones responsible
Acronym: Pink Pyramid (a type of “form”/”shape”) = Parvocellular pathway
what detects motion?
Magnocellular pathway: has high temporal resolution (think time,
motion) resolution [encodes motion]. But has poor spatial resolution; no
color).
Rods responsible.
Acronym: Motion = Magnocellular pathway
Parallel Processing:
detect/focus all information (color, form, motion) at same time.
