Karius Special Senses: Vision Flashcards
Direction of light rays for object that is far away
only parallel light rays enter the eye, little refraction to focus on retina
Direction of light rays for object that is nearby
the light rays are still diverging, need more refraction to focus on retina
Refraction
bending of light
Where is the first site that refraction occurs
cornea- bends light the most
Damage to cornea
very impactful on vision ex. astigmatism
2 parts of the eye that bend light?
cornea and lens
Why do we need the variable refraction provided by the lens?
to see things that are closer or far away
What does accommodation require
ciliary muscle, suspensory ligaments, lens itself
What happens to the lens during accommodation
make lens rounder
Function of ciliary muscle and suspensory ligaments during accommodation
control how thick the lens is
Ciliary muscle and suspensory lig during near vision
ciliary m contracts and tension on suspensory lig is released (becomes slack)
Shape of lens during near vision
becomes globular due to natural elasticity of lens
Increase curvature of the lens and refractive power
proportional - increased curvature increases refractive power
What does increased curvature of the lens do to light rays
allows nearby object to be bent sufficiently onto the retina
Ciliary muscle and suspensory lig during far vision
Ciliary muscle relaxes and tension of suspensory lig is increased
Lens shape during far vision
flattened
Decreased curvature of the lens and refractive power
proportional - decreased curvature decreases the refractive power
2 changes specific to near vision
convergence of eyes to point of focus and constriction of pupil
Pupil constriction for near vision
eliminates some of the diverging light rays
ex. squinting eyes when can’t see- its reducing the opening of light and allowing us to focus better
Retina cell types
photoreceptors, bipolar, ganglion, horizontal, amacrine
What retina cell types make up direct pathway of light to optic nerve
photoreceptor, bipolar, ganglion cells
What retina cell types are part of processing in the retina
horizontal and amacrine
Cells of vertical pathway of retina
photoreceptor, bipolar, ganglion cells
Vertical pathway function
relaying visual information to the brain
Base for the vertical pathway
cones - color, high detail, require a lot of light
Amino acid released by photoreceptors
glutamate
Glutamate release when dark
high release, depolarization occurs
What happens when photon activates photoreceptor
decrease glutamate release, hyperpolarization occurs
Vertical pathway for cones
photoreceptor struck by photon of light –> hyperpolarization –> decrease glutamate release into BIPOLAR cell
2 kinds of bipolar cells
ON-center and OFF-center
ON-center bipolar cells
cause depolarization in center of cell and hyperpolarization surrounding the cell
OFF-center bipolar cells
cause hyperpolarization in the center of the cell and depolarization surrounding the cell
ON-center vertical pathway cones
metabotropic receptor is activated, decrease in cation influx
ON-center in the dark cones
ON-center is hyperpolarized, increase in glutamate
ON-center with light cones
ON-center is depolarized, decrease release of glutamate
OFF-center vertical pathway cones
AMPA receptor activated and increase in cation influx
OFF-center in the dark cones
OFF-center is depolarized due to less sodium release and lots of glutamate
OFF-center with light cones
OFF-center is hyperpolarized, glutamate is decreases, AMPA not activated
Components of Vertical pathway for Rods
rods, ON-center bipolar cells, A11 amacrine, cone ON-Center, ganglion cell
Process of vertical pathway for rods
Rods converge on ON-center bipolar cells –> synapse on A11 amacrine cell –> synapse on Cone ON-center bipolar cell –> activated ganglion cell
Rods
low light, not great on detail
What cell expresses metabotropic receptor because it’s an “ON” cell
ON-center bipolar cell
A11 amacrine cell
tells you that you’re in the rod pathway
What does the ON-cell center tell us
where something is
What does the OFF-center tell us
where it ends
Amacrine and horizontal cell function
provide inhibitory signals that modify the activity of neighboring photoreceptors, bipolar cells, or ganglion cells
Where do action potential occur
ganglion cells
What does each eye see?
sees two different visual fields to give depth perception
Left temporal retina
activated by light coming from right visual field
Right nasal retina
activated by light coming from right visual field
Right temporal retina
activated by light coming from the left visual field
Left nasal retina
activated by light coming from the left visual field
What occurs at optic chiasma
all information from right visual field is sent to same part of the brain (ex. right visual field sent o left side of the brain)
Visual field
what you see
Retinal field
light on retina
Lateral geniculate body
where axons travel and synapse
Function of LGN
control motions of eye, control focusing, identify major elements within our visual image, identify motion
Primary Visual Cortex (V1) neocortex
divided into 6 layers that each have different functions
Layer 1,2,3 of primary visual cortex
allow networking between V1 and other parts of cortex
Layer 4 of primary visual cortex
receives inputs form the LGN, where synapse occurs, tells us what to focus on
Layers 5 and 6 of primary visual cortex
send information BACK to the LGN
Columns of cortex of primary visual cortex
each column runs perpendicular to surface and has 6 layers. each column has different function
Neighboring columns
have related jobs
Macula of the retina
have lots of columns and receive info from macula
Peripheral regions of retina
less area in V1
Major job of V1
identify the edges/contours of the visual image
Major job of V2
Identify disparities in the visual images presented by the two eyes
Determines depth perception
Blobs
enable color detection, located in each colun
What does accurate color detection depend on
all 3 sets of cones
Major role of V4
complete processing of the color inputs
What can these layers NOT do
name the image, copy the image, aim at the image, recognize the image
Higher processing of visual inputs
dorsal and vental pathway
Dorsal pathway
relay info to motor cortices to act on visual input
ex. allows playing catch with friends
Ventral pathway
relay info to “processing of sensory input” area
ex. naming object and copying he object
Damage to temporal lobe
can impair either naming/recognizing of an object and not impair the other
Special function of temporal lobe
recognizing faces
