PHYS physiology of the visual system Flashcards
(25 cards)
where is the first site of refraction
cornea
accounts for 2/3 of light bending
relationship between roundness and refraction
rounder = more refraction flatter = less refraction
what happens when ciliary m contracts
allows suspensory ligaments to loosen
allows lens to take a rounder shape
used for near vision
what happens when ciliary m relaxes
suspensory ligaments tighten
causes a flatter lens shape
used for far vision
presbyopia
lens becomes stiffer in aging, loss of elasticity
5 types of neurons in the retina
vertically oriented
horizontally oriented
Vertical:
receptor cells (rods and cones)
bipolar cells
ganglion cells (subtype:MG cells)
horizontal:
horizontal cells
amacrine cellswhere is the density of cone receptors the most
center of eye
rods-periphery-ish. peak at 20 degrees
what NT do rods and cones release
glutamate
when is glutamate release the highest (in what environment)
in the dark
photons in light stimulate and hyperpolarize the cells
on center bipolar cells
what depols
what hyperpols
compare to off center bipolar cells?
activation of photoreceptors in the center of the bipolar cell’s receptive field depols
activation of photoreceptors in the periphery of the bipolar cell’s receptive field hyperpols
off center bipolar cells- opposite
effects of glutamate receptor in depolarizing bipolars
GPCR that closes cGMP-gated ion channels similar to light transduction photoreceptors. channels open when less glutamate is present
allows for sign change – depol. leads to closure of
channel (opposite what you might think)
ON-center bipolars
effects of glutamate receptor in hyperpolarizing bipolars
common, excitatory glutamate receptor (non-NMDA recptors: AMPA and kainate)
no sign change
OFF-center bipolars
activation of an on center bipolar cell by a cone photoreceptor (in dark)
glutamate activates Gi GPCR-metabotropic receptor
results in decrease in cation influx (depolarizing bipolar)
hyperpolarizes cell
activation of an on center bipolar cell by a cone photoreceptor (in light)
light decreases amount of glutamate present
less Gi signaling
increase of cation influx
depolarizes the cell
activation of an off center bipolar cell by a cone photoreceptor (in dark)
glutamate activates AMPA
increase of cation influx
depol. of cell
activation of an off center bipolar cell by a cone photoreceptor (in light)
light decreases amount of glutamate
less activation of AMPA
decrease in cation influx
hyperpol. of cell
f(x) of on and off center cells
help us increase the ability to detect edges and sharpen our vision
on center – tells us where something is
off center – tells us where something ends
direct targets of the retina (nuclei and structures)
LGN superior colliculus pretectal area hypothalamus accessory optic nuclei
V1
primary visual cortex (brodmann area 17)
identify edges and contours of objects
V2
greater part of brodmann 18
depth perception by analyzing the disparities between the two eyes
V3
narrow strip of brodmann 18
identification of motion (3a)
V4
area 19
complete processing of color inputs
V5
middle temporal (MT) area (Part of 19)
Dorsal pathway “where pathway”
from primary visual cortex to parietal/frontal cortex
primary path associating vision with movement
completes motor acts based on visual input
passes through V3
