lecture 7 and 8- vision Flashcards
define refraction
bending of light waves at an angulated surface of a transparent material
define degree of refraction
amount of bending of light
what does degree of refraction depend on
ratio of the 2 refractive indices of the 2 transparent media and the degree of angulation between the interface and the entering wave front of the light waves
define refractive index
ratio of the velocity of light in air to the velocity of light traveling in the substance
define refractive power
measure of how much a lens bends light waves
define a diopter
1 diopter= 1 meter divided by the focal length of a lens
define focal point
point through which all parallel rays of light will pass after passing through each part of the lens
define focal length
distance from the center of the lens to the focal point
what does the iris do
controls the amount of light entering the eye from darkness to light conditions and plays role in depth of focus
define emmetropia
normal eye with regard to depth of focus. all distant objects can be seen clearly
define hyperopia
farsightedness usually due to an eyeball that is either too short or a lens system that is too weak; all distant objects can be seen clearly
define myopia
nearsightedness due to too long of an eyeball
define visual acuity
measure of the resolving power of the eye
what is the max visual acuity for 2 point sources of light
2 micrometers
define glaucoma
build up of fluid pressure in the eye
what is a tonometer sued for
used to measure the intraocular pressure
what is the normal intraoccular pressure
15 mm Hg
what is the photosensitive pigment in rods
rhodopsin
describe the outer segment of rods/cones
site of light sensitive photochemicals
describe the inner segment of rods/cones
contains organelles, especially mitochondria
describe the synaptic body of rods/cones
connects with horizontal and bipolar cells
what does excitation of rods cause
increased negativity of the intrarod membrane potential (hyper polarization)
what does decomposition of rhodopsin do
decreases rod membrane conductance for sodium ions in the outer segment
what colors are cones sensitive to
blue, green and red
list the layers of the retina in order
photoreceptors, horizontal cells, bipolar cells, amacrine cells and ganglion cells
define the plexiform layer
layer of synaptic connections
where do photoreceptors transmit signals to
outer plexiform layer
what do photoreceptors synapse with
bipolar cells and horizontal cells
what type of signals do horizontal cells do
transmit signals from rods and cones to bipolar cells and transmit signals to outer plexiform layer
where do bipolar cells transmit signals from
rods, cones and horizontal cells
where do bipolar cells transmit signals to
inner plexiform layer
what do bipolar cells synapse with
amacrine and ganglion cells
describe the signals of amacrine cells
transmit signals directly from bipolar to ganglion cells; within inner plexiform layer from axons of bipolar cells to dendrites of ganglion cells or to other amacrine cells
where do ganglion cells transmit signals from
retina to brain
what type of cell axons make up optic nerves
ganglion cell axons
what do interplexiform cells transmit signals from
from inner plexiform layer to outer plexiform layer (retrograde)
what type of neurons are in the direct pathway of foveal region
cones, bipolar cells and ganglion cells
what type of neurons are in the pure rod vision
rods, bipolar cells, amacrine cells and ganglion cells
what neurotransmitter is used by rods and cones (bipolar cells)
glutamate
what type of neurotransmitters are used by amacrine cells
there are more than 8, but all of them are inhibitory
what is the main role of amacrine cells
interneurons that help analyze visual signals before they leave the retina
where is visual acuity strongest
central retina (central fovea)
what is the peripheral retina most sensitive to
weak light
how fast do W ganglion cells transmit signals
8 m/sec
describe the fields of W ganglion cells
broad fields in peripheral retina because their dendrites spread widely in the inner plexiform layer
where do W ganglion cells get most of their excitement
from rods transmitted by way of small bipolar cells and amacrine cells
how fast do X ganglion cells transmit signals
14 m/sec
describe the fields of X ganglion cells
they have small fields (signals represent discrete retinal locations)
what type of ganglion cells are likely responsible for all color vision
X ganglion cells
how fast do Y ganglion cells transmit signals
50m/sec or faster
where does the dorsal lateral geniculate nucleus receive input from
optic nerve
how does the dorsal lateral geniculate nucleus relay info from optic tract to visual cortex
optic radiation (geniculoalcarine tract)
what layers of the lateral geniculate nucleus receive signals from lateral half of ipsilateral retina
2, 3 and 5
what layers of the lateral geniculate nucleus receive signals from medial half of opposite retina
1, 4, and 6
where do layers 1 and 2 of the dorsal lateral geniculate nucleus receive input from and what type of vision do they transmit and what type of layers are they
from large Y type ganglion cells and transmit only black and white. They are magnocellular layers
where do layers 3-6 of the dorsal lateral geniculate nucleus receive input from and what type of vision do they transmit and what type of layers are they
from large X type ganglion cells and transmit color and are parvocellular layers
define transmission gating and what controls it
controlled by lateal geniculate nucleus and it is the control of how much signal is allowed to pass to the cortex
what is the source of gating control
corticofugal fibers from primary visual cortex and reticular areas of mesencephalon
where is the primary visual cortex located
occipital lobes
where do geniculocarine fibers mainly terminate
in layer 4
where do signals from Y ganglion cels terminate in the primary visual cortex
layer IVc-alpha
where do signals from X ganglion cells terminate in the primary visual cortex
layer IVc-beta and IVa
where are color blobs located
among the columns of the secondary visual areas
where do color blobs receive lateral signals from and how are they activated
from adjacent visual columns and are activated specifically by color signals
what do meridional fibers do
control and release tension in the lens
what do circular fibers do
decrease tension in lens
what cranial nerve controls both sets of ciliary muscles
CN III
