vision Flashcards
the most sense humans rely on (the dominant sense)
vision
nearly ___% of all the sensory receptors in our whole body are in the eyes
70
light is
electromagnetic energy
the visible part of the electromagnetic spectrum ranges from
400 nm to 700 nm
sclera
- the tough outer coat, that extends from the cornea to the optic nerve
- protects the entire eyeball
choroid
- a vascular layer
- contains blood vessels that nourish the inner parts of the eye
cornea
- the front portion of the eye, convex in shape
- where light enters the eye
iris
- located just behind the cornea
- regulates the amount of light entering the eye by adjusting the size of the pupil
pupil
- a black hole in the middle of the iris
- its size increases/decreases depending on the intensity of light entering the eye
pupil dilation
mydriasis
pupil constriction
miosis
mydriasis is caused by
- low light conditions
- sympathetic NS activation
- certain meds
- attraction/interest
miosis is causes by
- bright light conditions
- parasympathetic NS activation
- certain meds
- age
- accommodation reflex
eye lens
- made up of a transparent jelly-like substance made up of proteins
- held in position by ciliary muscles and suspensory ligaments
ciliary muscles and suspensory ligaments
adjust the focal length of the eye so that we can see distant & nearby objects clearly
the ability of the eye to focus on distant and nearby objects by changing the focal length is
accommodation
aqueous humor
- a viscous liquid filled in the area between the cornea and the eye lens
- prevents the eye lens from collapsing due to changes in atmospheric pressure
retina
a delicate membrane having a large number of light-sensitive cells situated at the back of the inner eye
light-sensitive cells are of two types
- rod cells
- cone cells
rods
respond to the intensity of light
cones
respond to the color of the object
fovea
- a tiny dimple located in the middle of the retina
- the center of the eye’s sharpest vision and location of most color perception
- where max number of cones are
an _____ image of an object is formed on the retina
inverted
the electric signals generated by the cells are sent to the brain through the
optic nerve
optic disk
- where all the axons of the ganglion cells exit the retina to form the optic nerve
- is insensitive to light, therefore called the blind spot
assuming an individual has just been hit with a blinding flash light beam, what is the first step in seeing?
- that light hits the posterior retina
- spreads from the photoreceptors to the bipolar cells just beneath them
- then to the innermost ganglion cells where they then generate action potentials
what is the second step in seeing
the axons of all those ganglion cells weave together to create the thick ropey optic nerve (the second cranial nerve) which leaves the back of the eyeball
what is the third step in seeing
the optic nerve carries those impulses up to the thalamus and then into the brains visual cortex
the thalamus
- massive gray matter in the forebrain
- relays sensory signals (visual + pain perception)
occipital lobe
associated with the visual processing and contains most of the anatomical region of the visual cortex
the primary visual cortex is
Brodmann area 17 (or V1)
ventral stream in visual processing
involved in object processing
ex: color, texture, shape, size
damage to the ventral stream leads to
- impairment in object and face perception
- impairs contrast sensitivity, depth perception
prosopagnosia
the inability to recognize familiar faces
dorsal stream in visual processing
involved in spatial processing
ex: location, movement, spatial transformationa/relations
damage in the dorsal stream leads to
- simultanagnosia
- optic ataxia
- hemispatial neglect
- akinetopsia
- apraxia
function, sensitivity, and location of cones
function - enable to perception of fine detail and color
sensitivity - operate best under bright conditions (high activation threshold)
location - mostly in central region of retina (fovea)
function, sensitivity, and location of rods
function - vision in low-light conditions, detecting movement, providing peripheral vision
sensitivity - highly sensitive to light, don’t detect color but variations in brightness
location - around the periphery of the retina
enabling more effective peripheral vision
rods
enabling more effective central vision
cones
3 types of cones (sensitive to different ranges of light wavelengths)
S cones
M cones
L cones
S-cones
correspond to short-wavelength
M-cones
medium wavelength
L-cones
long wavelength
trichromatic vision
humans usually have 3 kinds of cones (or 3 color pigments)
color blindness
an eye condition that results from the destruction of cone cells from disease
- individuals are unable to differentiate various colors
monochromacy
a type of colorblindness where people see the world in grayscale (black, white, grey)
most common type of colorblindness
red-green colorblindness
tetrachromatic vision
- having 4 or more cones
- more intense color vision
