Vision Flashcards
Cornea
- front of eye
- clear, dome-like structure that allows light to enter into eye
- gathers and focuses incoming light
Pupil
light for cornea enters this gap in the iris
Iris
- color portion of the eye
- regulates size of pupil with its contractile muscles – smaller iris = larger pupil and vice versa
What happens to pupil when exposed to bright light?
- pupil will constrict to protect retina
- involuntary muscles in iris relax
What happens to pupil in the dark?
- pupil will dilate to get more light into retina
- involuntary muscles in iris contract
Lens
- located behind the iris
- focuses/refracts light to create a focal point
Fovea
- focal point of light located at the back of the eye
- only cones located here, no axons
Retina
- located at back of eye, innermost layer of eye
- translates photons in light into an electrical impulse that is transmitted to body via neurons
- “image detector”
Optic Nerve
sends information from retina to brain
Retinal Cells
- rods and cones
- light absorbing cells of the retina
- responsible for transduction of photons into an electrical signal
Structure of Rods and Cones
- contain mitochondria and nucleus
- light absorbing portion (membrane shelves lined with rhodopsin) face back of the eye
- specialized synapse facing front of eye so they can transduce electrical signal to other cell types that carry signal to optic nerve
Rods
- contain single rhodopsin pigment
- low sensitivity to detail
- permit night vision
- no color perception
- normally turned on but turn off when light hits
- mostly found in periphery
- slow recovery time
Cones
- contain 3 different types of photopsin pigments
- sensitive to both color and detail
- absorb light in red/green/blue spectrum
- best in bright light
- concentrated at fovea
- fast recovery time
Bipolar Cells
- first cells that receive light
- direct input from rods/cones
- highlight gradients
- pass signal to ganglion cells
Horizontal and Amacrine Cells
- two cell types that affect the bipolar cell before they send signal to ganglion cells
- work together to take information from multiple retinal cells to detect edges and contrasts
Ganglion Cells
- receive information from many retinal cells
- group to form the optic nerve
Conjunctiva
first layer of eye that light hits
Anterior Chamber
- space in eye that is filled with aqueous humor
- provides pressure to maintain shape of eyeball
Sclera
- whites of eye
- thick fibrous tissue covers posterior 5/6th of eyeball
- attachment point for muscles
- does not cover cornea
Choroidal Vessels
blood vessels that supply nutrients to the eye along with the retinal vessels
Posterior Chamber
- area behind cillary muscle
- filled with aqueous humor
Dilator Pupillae
opens pupil under sympathetic stimulation
Constrictor Pupillae
constricts pupil under parasympathetic stimulation
Blind Spot
- located where the optic nerve connects to the retina
- no rods or cones found here
Macula
part of retina that is rich in cones
Ciliary Body
- portion of eye that produces aqueous humor
- accommodation of lens
Canal of Schlemn
drains aqueous humor
Suspensory Ligaments
- change shape of lens
- if ciliary muscle contracts it pulls on these
Vitreous Chamber
- filled with vitreous humor
- jelly-like substance that provides pressure to eyeball
List the structure of the eyeball in order of where light enters
- cornea
- pupil
- lens
- vitreous
- retina (rods/cones -> bipolar cells -> ganglion cells)
- optic nerve
- optic chiasm
- optic tract
- LGN of thalamus
- radiations through parietal and temporal lobes
- visual cortex in occipital lobe
Magnocellular Cells
- located in the LGN of the thalamus
- responsible for motion
Parvocellular Cells
- located in the LGN of the thalamus
- responsible for shape
Optic Discs
- found in rods
- large membrane bound structures that contain proteins that fire APs to brain
Describe the pathway that occurs when light hits rod/cone
- light hits small molecule called retinal inside of protein rhodopsin and causes retinal to change conformation from bent to straight
- transducin breaks from rhodopsin and alpha from transducin binds to phosphodiesterase (PDE)
- PDE converts cGMP to GMP which leads to closing of Na+ channels (occurs b/c Na+ channels need bound cGMP to open)
- rods hyperpolarize and turn off; glutamate is no longer released and no longer inhibits ON bipolar cells
- ON bipolar cells activate retinal ganglion cell which sends signal to optic nerve in brain
Optic Chiasm
- where nasal fibers from left and right eye cross
- visual information from left side of each eye goes to left hemisphere of brain
Everything in ____ visual field is processed by the left hemisphere and vice versa.
right
List the 3 areas of the brain where vision is processed
(1) lateral geniculate nucleus: part of thalamus
(2) visual cortex: part of occipital lobe
(3) superior colliculus: midbrain, constitutes tectum
Parallel Processing
- ability to identify key characteristics in an image and apply those characteristics to a memory in order to recall a word or title to describe the object in the image
- Ex. see picture of cheetah and recognize tan fur, small black spots etc then recall and associate word “cheetah”
Feature Detection
- recognition of features to identify desired object in visual field
- Ex. how do you find a friend in a crowd? if friend said they have green shirt on then brain automatically filters and focuses on people wearing green
