Physiology of Vision - Metz Flashcards
the retina of the eye is responsible for converting the _________ waves of light stimuli into _________
electromagnetic ; electrical signals
At a basic level, the photoreceptors of retina (eye) is capable of detecting two different qualities of light, what are they
brightness ; light
A large aperture would allow a ____ amount of light to pass through
large
a small aperture would allow a _____ amount of light to pass through
smaller
The pupil is an aperture that
controls the amount of light transmitted to the interior of the eye –> this process is controlled by the
autonomic nervous system
The iris is innervated by both the ______ and ______ divisions of the nervous system
sympathetic ; parasympathetic
When a bright light strikes the eye, the ________ nervous system facilitates _______
of the pupil via stimulation of the _______
** This reflex will occur bilaterally in both eyes, even if only one eye has been exposed to the high intensity light **
parasympathetic ; constriction ; circular muscles
When the eyes are exposed to a darker environment, the _______ nervous system
stimulates ______ of the radial muscles, leading to pupil ______
sympathetic ; constriction ; dilation
The pupillary reflex is important because it regulates the _______ falling upon the retina, and also protects the retina from overexposure to light
intensity of light
the aperture also affects the
depth of field (sharpness)
A large aperture will result in a larger ________ aka a larger
amount of blur in the background
depth of field
For closer vision, ciliary muscle ______ via ______ stimulation
contracts ; PS
for closer vision, tension on suspensory fibers is
reduced
for closer vision, the lens becomes more
spherical
for closer vision, the focal power is ______ for near vision
increased
_____ occurs when light passes between two different mediums
Refraction
To focus on closer objects, the eye must ______ its focal power through a process called ______
increase ; accommodation
High concentration of photoreceptors in the
fovea
a relaxed ciliary muscle = a _____ lens
flat
a not-relaxed ciliary muscle = lens is
round
in myopia/near-sightedness - the axis of the eye is
too long
correction for myopia/near-sightedness = ____ lens that ____ the light
concave ; diverges
in hyperopia/far-sightedness - the axis of the eye is
too short
correction for hyperopia/far-sightednesss = ____ lens that ____ the light
convex ; converges
in hyperopia/far-sightedness, the image is focused ____ the retina
behind
the lens becomes _____ elastic with age so the ability to accommodate _____
less ; decreases
Presbyopia causes difficulty seeing
near objections
to correct presbyopia = _____ lens that _____ the light
convex ; converges
uneven curvature of cornea and/or lens
astigmatism
an astigmatism = the image is _____ on the retina
unfocused
to correct an astigmatism = ____ lens that _____ the light
cylindrical ; appropriately focuses
the photoreceptors that are
responsible for detecting light are in the _____ regions of the retina
deeper
The ganglion cells are the _____ of the retina, and their axon fibers are arranged in the _____
output ; optic nerve
Photoreceptors are
rods and cones
pigment epithelium absorbs
photons
rods and cones send _____ signals
electrical
The sensory receptors in the retina are called
photoreceptors
photoreceptors are responsible for converting the
_______ signals from photons into the ______ signals of the
nervous system
electromagnetic ; electrical
3 types of cones
red, green, blue
cones see ____ vision ; rods = ______ vision
color ; black & white
rods work best for ____ vision and cones work best for ____ vision
(hint = what time)
night ; day
rods are ______ to low-light intensitity
sensitive
cones are not sensitive to
low-intensity light
rods are associated with _____ accuity
low
cones are associated with _____ accuity
high
rods are not present on the
fovea
cones are present on the
fovea
Both rods and cones contain outer segments comprised of
photoreceptor disks
Both rods and cones have inner segments which contain the
nucleus, mitochondria, and other cellular organelles
The base of the photoreceptors
contain _______ that communicate with the _______ layer of the eye
synaptic bodies ; neural network
In these cellular membranes of the disks are embedded molecules of ______
photopigments
For rods, the photopigment is called ______
rhodopsin
The detection of light by the photopigment leads to the
conversion of ______ to ______
11-cis-retinal ; all-trans-retinal
The conversion of 11-cis-retinal to all-trans-retinal leads to a complex signaling cascade that
initiates several downstream effects via a
G-protein pathway
When rods are in a DARK environment, an enzyme in the cytosol called guanylyl cyclase
continuously converts _____ into _____
GTP ; cGMP
When rods are in a DARK environment
cGMP leads to activation of ________ channels in the plasma membrane of the _____ segment
non-selective cation
channels ; outer
When rods are in a DARK environment
The non-selective cation
channels allow sodium
molecules to diffuse down their electrochemical gradient from the extracellular fluid into the _____ of the ____
cytosol ; rod
When rods are in a DARK environment
The movement of this Na+ into the cell produces a _____ of the cell
depolarization
When rods are in a DARK environment
The depolarization of the cell stimulates the release of the neurotransmitter
______ from the _____ of the rod
glutamate ; synaptic end bulb
When rods are in a LIGHT environment
When a photon of light is detected by a pigment in rods called ________ , the compound _________ is converted to _________
rhodopsin ; 11-cis retinal ; all trains retinal
When rods are in a LIGHT environment
The conversion of 11-cis retinal to all trains retinal stimulates an associated G-protein called _________ to exchange its
bound _____ for ______
transducin ; GDP ; GTP
When rods are in a LIGHT environment
Once GDP is exchanged for GTP, the activated _____ subunit of the G-protein then dissociates from the _______
alpha ; beta-gamma complex
When rods are in a LIGHT environment
The activated alpha subunit of the G-protein then dissociates from the beta-gamma complex leads to the activation of the enzyme ________________, which
catalyzes the breakdown of
_____ into ______
cGMP phosphodiesterase ; cGMP ; 5’GMP
When rods are in a LIGHT environment
the breakdown of cGMP ; 5’GMP decreases the cytosolic levels of ______ , leading to closure of a _____ channel in the plasma membrane
cGMP ; non-selective cation
When rods are in a LIGHT environment
The closure of the non-selective cation channel in the plasma membrane causes a drop in sodium _____ which leads to _______ of the plasma
membrane, as the membrane potential become more ______ than at rest
influx ; hyperpolarization ; negative
In the dark, cGMP levels are _____, and this allows for the non-specific cation channels in the plasma membrane of the outer segment to be ____
high ; open
in the dark
Sodium will be removed from the cytosol in the inner segment via a ______, leading to the “________”
sodium-potassium pump ; “dark current”
In the light, as the cGMP levels _____, cellular reactions lead to a _____ of these same non-
specific cation channels
decrease ; closure
in the light, ____ sodium enters the cell, leading to a ______ of the plasma membrane and a ______ in the release of neurotransmitters from the ______
less ; hyperpolarization ; decrease ; synaptic end bulb
In the light the decrease in the release of neurotransmitters from the synaptic end bulb would ______ the release of ______ during exposure to light
decrease ; glutamate
the downstream effects of the neurotransmitter glutamate can be either ______ or ______, depending on the type of receptors activated on the bipolar or horizontal cells
excitatory ; inhibitory
The bases of the photoreceptors contain synaptic bodies that communicate with the neural
network layer of the eye and is comprised of 3 cell types, what are they?
bipolar
horizontal
amacrine
Due to the thinness of the retina and the close proximity of these structures, the photoreceptors and interneurons can
communicate effectively using _______
graded potentials
The ganglion cell layer is responsible for integrating all of the information from the ______ cells and sending ______ via their axons in the ______
upstream ; electrical signals ; optic nerve
The bases of the photoreceptors contain a synaptic body that releases neurotransmitters onto
the ______ cells
bipolar cells
Rods are located at the ______ of the retina, and many rods synapse onto a _______ cell
periphery ; single bipolar
Rods have a high level of ______ with as many as 300 rods ______ onto a _____ cell
convergence ; converging ; single ganglion
Rods have a high level of convergence = this results a _____ sensitivity of rods, as light striking any of these rods could _____ the bipolar cell
higher ; activate
Rods have a high level of convergence - this results a higher sensitivity of rods - this arrangement also produces a _____ acuity in rods
lower
the clearness or sharpness of vision
acuity
there are relatively _____ cones that converge on a ____ cell
few ; ganglion
In the fovea, the ratio of cones to ganglion cells is almost _____
1:1
There are relatively few cones that converge on a ganglion cell. In the fovea, the ratio of cones to ganglion cells is almost 1:1. This allows for ________ of the color image, but ______ light sensitivity
greater sharpness/acuity ; lower
High sensitivity
Low acuity
periphery of the retina
periphery of the retina has a ______ of rods and cones
mixture
periphery of the retina - many rods ______ onto a single ganglion cell
synapse
low sensitivity
high acuity
center of the retina : fovea
cones only
center of the retina : fovea
1:1 ratio of cones to ganglion cells
center of the retina : fovea
