Physiology of the Visual System Flashcards
How does the shape of the lens affect incoming light refraction?
rounder = more refraction
flatter = less refraction
How does the ciliary m affect the shape of the lens?
contracts –> allows suspensory L to loosen –> rounder lens –> near vision
relaxes –> suspensory L tight –> flatter lens –> far vision
What is presbyopia?
the lens becomes stiffer in aging, loss of elasticity
What are the 5 neuron types in the retina?
vertically oriented:
receptor cells - rods and cones
bipolar cells
ganglion cells (subtype: MG cells)
Horizontally oriented cells:
horizontal cells
amacrine cells
What do rod cells detect and how do they converge?
a lot of convergence: many rods + many bipolars –> one ganglion cell
operates in dim light
sacrifice acuity to gain sensitivity
What does the cone system detect?
less convergence: receptor –> one bipolar cell –> one ganglion cell
maximizes acuity
colors and bright light
Wher are rods and cones most dense on the retina?
cones: most dense at fovea
rods: peak laterally about 20 degrees
What is glutamate release like in dark and light?
Highest when it is dark –> no stimulation by photons
Glutamate is Lowest when there is Light –> cells hyperpolarize
How do cones activate bipolar cells?
photon stimulates photoreceptor
photoreceptor hyperpolarizes
glutamate release on bipolar cell decreases
How do ON-center bipolar cells react to light?
Light: less glutamate –> activation of photoreceptor in center –> depolarization of bipolar cell
dark: glutamate –> Gi activation in periphery –> hyperpolarization of cell
tell you where something is
How do OFF-center bipolar cells react to light?
activation of photoreceptor in center of receptive field –> hyperpolarization of cell
activation of photoreceptor in pheriphery –> depolarization
Dark: glutamate –> AMPA receptor –> increase cation influx –> depolarization
tell you where something ends
How does glutamate affect ganglion cells?
bipolar cell activated –> glutamate –> depolarizes ganglion
How do rods affect bipolar cells?
many rods converge on one ON-center bipolar –> connects to a rod-bipolar cell and a rod amacrine cell –> cone-bipolar cell –> ganglion cell
How do amacrine and horizontal cells affect other cells in the retina?
provide inhibitory GABA/glycine to other cells
What does the pretectum do in vision?
modulates the pupillary light reflex
What is V1?
primary visual cortex
brodmann area 17
identifies contours
What is V2?
greater part of brodmann 18
parastriate complex
identifies depth perception
What is V3?
narrow strip of Brodmann 18
parastriate cortex
V3a: identification of motion
What is V4?
brodmann 18
completes processing of color inputs
WHat is V5?
middle temporal area (part of 19)
What do the layers of the primary visual cortex do?
I, II, III allow for networking btw V1 and other areas of the cortex
Layer IV: receives input frm LGB (large here)
Layers V and VI: main output layers to LGB, thalamus, subcortical regions
What are ocular dominance columns?
span all 6 layers
cells in one column respond to one eye, the next column responds to the other eye
columns alternate btw L and R eyes
What do orientation columns do?
in primary visual cortex
span all 6 layers
excited by visual line stimuli of varying angles
oriented perpendicular to cortical surface
What do blobs do in the primary visual cortex?
span all 6 layers
organized region of neurons that are sensitivet to color
all 3 color-coding cones are required for accurate color detection
What are the 3 types of cones?
S cone = blue cone
M cone = green cone
L cone = red
What are the patterns of mapping each type of column in the primary visual cortex?
ocular dominance = stripes
orientation columns = swirls
blobs = blobs
What is the dorsal pathway?
the “where” pathway
from V1 –> thru V3 –> to parietal/frontal cortex
completes motor acts based on visual input
What is the ventral pathway?
the “what” pathway
Vfrom V1 –> inferior temporal cortex
interprets images and complex patterns
copying and naming are separate fxns
facial recognition is a specialized area
What are MG cells?
subset of ganglion cells
detect light directly via blue-sensitive pigment melanopsin –> change in Ca levels in MG –> project directly to suprachiasmatic nucleus of hypothalamus
manages circadian rhythms
How does glutamate affect metabotropic and ionotropic receptors and where are they found?
glutamate –> Gi –> closes channels –> cell hyperpolarizes
light –> less glutamate –> less Gi signaling –> depolarization = On-center bipolar cells
dark –> glutamate –> AMPA –> depolarizes cell
see AMPA in off-center bipolar cells = tell you where light/object stops
