Lecture 6 Flashcards
outer layer of eye composed of white, fibrous tissue
sclera
transparent front part of eye that controls 80% of the focusing power
cornea
What are the outer structures of the eye?
sclera
cornea
What are the middle structures of the eye?
iris
pupil
ciliary body
colored portion of eye; contains muscles that adjust pupil size
iris
open during dim light, closed during bright light
pupil
ring of tissue that circles the lens; made of muscle and vasculature
ciliary body
What are the internal structures of the eye?
retina
lens
aqueous humor
vitreous humor
part of the eye that detects light, processes information, and sends it to the brain
retina
changes shape to allow fine focus
lens
provides nutrients to anterior eye
aqueous humor
provides shape, contains macrophages that remove debris
vitreous humor
contraction of lens by ciliary muscle
focus
Each eye sees ___ degrees of arc in a horizontal plane, __ degrees nasally and __ degrees temporally.
150
50
100
What is the role of the retina?
converts light energy into action potentials
What are the 5 types of neurons found in the retina?
photo receptors biopolar cells ganglion cells horizontal cells amacrine cells
What is the basic unit of transmission in the retina?
photoreceptor > bipolar cell > ganglion
make up to outer nuclear layer of the retina
photorecepters (rods and cones)
make up the inner nuclear layer of the retina
interneurons (horizontal, bipolar, amacrine cells)
make up the ganglion cell layer of the retina
output neurons (retinal ganglion cells)
The plexiform layers of the retina contain ____.
synaptic connections
made up of axons that carry optic information to the brain
optic nerve
The photoreceptors are located at the ___ of the retina.
back
What are the two light receptors in the retina and what kind off light do they detect?
rods - low light
cones - bright light
Photoreceptors absorb light and then transduce to ___ than ____ signals in the outer segment. Then the signals transduce again to ___ signals in the synaptic terminal.
chemical
electrical
chemical
There are no ____ in the photoreceptors. Projections are ___. Light causes ____ that leads to ___ transmitter release.
action potentials
short
hyperpolarization
less
What is rhodopsin?
a GPCR found in the rods of the retina; extremely sensitive to light (good for low light)
Conversion of ____ in rhodopsin to _____ via a photon of light causes activation of ____ (light to chemical signal). Then, the ___ dissociates from ___ and ____ recycles to ___.
11-cis-retinal all trans retinal opsin retinal opsin trans-retinal 11-cis-retinal
vitamin A found in carrots
retinal
Activated rhodopsin activates a ____, which activates ____. That breaks down ___, which opens a cation channel for __ and __ in the photoreceptor outer segment. This ___ the cell. Light depletes ___, which closes the channel and ___ the cell.
G protein phosphodiesterase cGMP Na+ Ca+2 depolarizes cGMP hyperpolarizes
What is light’s role in rhodopsin activation?
- reduces sodium current through cGMP gated channels
- hyperpolarizes cell
- reduces vesicle release
Each activated rhodopsin can activate 100s of ____, each of which can activate many molecules of ____, each of which can hydrolyze 1000s of molecules of ____. One photon of light closes about ___ ion channels per second.
g proteins
phosphodiesterase
cGMP
200
What is the unique feature of rods?
detect a single photon of light, but black and white only (night vision)
What is a unique feature of cones?
can detect ~100 photons (less sensitive than rods), but can detect colors
night vision; active rods, light too dim for cones
scotopic
color vision; cones active, rods bleached (inactive)
photopic
How long does light adaptation take? What about dark adaptation? What accounts for the difference?
light: occurs quickly
dark: up to ~25 min
Rhodopsin is bleached in bright light and needs to regenerate
What are the 3 color-specific cones?
red (long wavelength))
green (medium wavelength)
blue (short wavelength)
What causes color blindness?
mutations in cone opsins
In which cones are mutations most common?
red or green opsins
Colorblind people have normal ____ because rods are more sensitive than cones.
light sensitivity
red-green colorblindness; long-wavelength cone affected (red)
protanopia
red-green colorblindness; medium wavelength cone affected (green)
deuteranopia
a rare condition in which the individual only has one working type of cone
total color blindness (monochromacy)
Colorblindness is often inherited: ____ and ___. About __% males and __% females will inherit it.
x-linked
recessive
8
0.4
The human retina has ____ rods and ____ cones.
91 million
4.5 million cones
central retina where cones are highly packed; absolute center is completely rod-free
fovea
There is high ___ in the fovea and greater ____ in the periphery.
visual acuity
light sensitivity
In the fovea, other cell layers are displaced. Why?
it allows light to hit cones with less interference
There are two types of bipolar cells. ON cells ___ with light while OFF cells ____ with light.
depolarize
hyperpolarize
In the dark, there is ___ glutamate release by the photoreceptor. OFF bipolar cells express ____ which is ___. They ____ from glutamate and ___ in firing in response to light. ON bipolar cells express ____ which is ____. They ____ from glutamate and ____ firing in response to light.
AMPA inotropic depolarize decrease mGluR metabotropic hyperpolarize increase
In the light, there is ___ glutamate release by the photoreceptor. OFF bipolar cells express ____ which is ___. They ____ from glutamate and ___ in firing in response to light. ON bipolar cells express ____ which is ____. They ____ from glutamate.
low AMPA ionotropic depolarize decrease mGluR metabotropic hyperpolarize increase
In the dark, OFF bipolar cells are ____ and ON bipolar cells are ____. In the light, OFF bipolar cells are ____ and ON bipolar cells are ____. In light, ON bipolar cells ___ the signal.
active inactive inactive active invert
Retinal ____ send APs to the brain and detect ____.
ganglion cells
light intensity
the area to which a particular RGC is responsive
receptive field
Receptive fields have ___ and ___ portions. ON-center ganglion cells ___ when light goes on. OFF-center ganglion cells ___ when light goes on.
center
surround
depolarize
hyperpolarize
What is a post-inhibitory rebound?
stimulation of nerve impulses after hyperpolarization
In the direct pathway of information processing in the retina, the bipolar cells connect ____.
directly to ganglion cells
In the indirect pathway of information processing in the retina, the bipolar cells connect ____.
to horizontal and machine cells which make lateral connections to the ganglion cells
In an ON center ganglion, a small spot of light leads to ___, while a large spot of light leads to ___. In summary, these ganglion cells respond better to ___ and high ___.
no inhibition
inhibition
well aimed small spots
contrast
In an OFF center RGC, dark light in the center leads to _____.
depolarization
Center-surround organization enhances sensitivity to ___ and ___.
edges
contrast
RGCs fire depending on ___ not absolute ____.
contrast
light intensity
Our visual system does not encode ____.
light intensity
streams of information related to different visual properties are dealt with simultaneously by different circuits
parallel processing
Receptive field properties get extracted as signal moves from photoreceptors to RGCs to brain and only ____ is transmitted.
relevant information
2 dimensional surface of the retina is mapped (topographically arranged) onto the surface of subsequent structures
retinotopy
All RGC axons exit the eye
at the ____ (blind spot) and form a large, myelinated nerve called the ___.
optic disk
optic nerve
point where optic nerve enters the brain
optic chiasm
The L visual field from ____ projects to R cortical hemisphere and vice versa.
both eyes
After chiasm, projections are called ____. These projections contain ____ and ____ RGC axons. They project to ___ of the dorsolateral thalamus and carry information about left visual field to ____ LGN and vice versa.
optic tracts ipsilateral temporal contralateral nasal lateral geniculate nucleus (LGN) right
The right LGN projects to ___ in ___ of the cerebral cortex.
right visual cortex
occipital lobe
Each LGN layer is eye-specific: ipsilateral eye projects to layers ___ and contralateral eye projects to layers ___.
2, 3, 5
1, 4, 6
Layers 1, 2 in the LGN are ___ (detect ___); receive input from ganglion cells that detect gross ___ and ____.
magnocellular
motion
shape
movement
Layers 3-6 are ___ (small cells, detect ___); receive input from ganglion cells that detect ___.
parvocellular
shape
shape
All layers of the LGN; detect color
koniocellular
___ RGCs innervate each LGN neuron and the visual receptive fields in LGN are almost ___ to those in retina.
1-2
identical
Magnocellular layers have a ___ center surround and detect ___ bursts and are ___ to color.
large
transient
insensitive
Parvocellular layers have a ___ center surround and detect ___ bursts and are ___ to color.
small
sustained
sensitive
In the occipital lobe, the upper visual field is represented ___ the calcarine sulcus, the lower field ___.
below
above
Fovea is represented on a huge amount of cortex because of its ___ and ___.
high sensitivity
density of cones
The visual cortex has _ layers, each with specific inputs and outputs. The LGN projects to layer _, output is layer 5. The largest input is to __ (magnocellular and most parvocellular)
6
4
5
4C
allow for segregation of visual input from each eye
ocular dominance columns
Axons from L and R eye are ____ in layer 4.
segregated
What happens during monocular depravation (i.e., close one eye) during development?
lose ocular dominance columns
Neurons in V1 respond strongly to a bar of light at a particular orientation and less strongly or not at all to other orientations. Why is this?
convergence of several center surround cells –> orientation sensitivity
Some cells in V1 are also ___ selective; respond strongly to lines/bars/edges moving in a ___ but not at all in the ____.
direction
preferred direction
opposite direction
Depth perception requires ___, ___ vision. Its based on the ___ of each visual field in a binocular cortical neuron. Some cortical neurons respond to visual objects ___ than the plane of focus, others ___ the plane of focus.
binocular aligned disparity of the position closer beyond
What are the binocular cues?
convergence
binocular disparity
What are the monocular cues?
linear perspective relative size/height shading aerial perspective texture
