Visual 2 Flashcards
These are mores sensitive to light and have slow integration time
rods
These have poor spatial resolution
rods
These have more pigment and are less directionally sensitive
rods
These are less sensitive to light and have fast integration time
cones
These give us high spatial resolution
cones
These hae less pigments and are directionally sensitive
cones
Per eye you have______ rods
and ____cones
100 million
5 million
Key dif btwn rods and cones are rods
saturate
At low levels of light, rod …
reaches its max response, at room level, rods are saturated
Most of the time,vision is based on
cones or 5% of photoreceptors
Photorecetpors _____ in response to light
hyperpolarize
Photopigment =
chomophore + opsin
Chromophore conformation is
11-cis retinal
photopig is embedded in
OS layer (80% OS is photopigment)
11-cis-retinal absobs light at
375 nm
Opsin will “_____” absorption spectrum
red shift
Changes in chromophore will….
initiate transduciton
what kind of protein receptor is photopigmetn
GPCR with chormophore burried in middle
rods absorb strongest in
blue-green
photopigments are characterized by:
efficiency with which they absorb light of diff wavelengths
photoreceptors cant register the wavelenth of photons the catch “the output depends on quantum catch, but not upon WHICH quanta are caught”
concenpt of univariance
Photoreceptors are _______
colorblind
How do we tell what dif types of colors we see
photoreceptors give input to ganglion cell based on quantam catch
Once we absorb light, begin phototransduction which begins with:
Isomerization: shift from 11-cis to all trans conformation as we slam against the transmembrane domain
Isomerization from 11-cis chromophore to all trans will cause:
activaiton of opsin protein
Once Opsin is activated, it will activate
transducin (g protein)
Once transducine is activated it will
activate PDE
PDE will do what to cGMP
turn it to GMP which closes ion channels
low cGMP closes ion channels resulting in
hyperpolarization (inward flux of Ca++ and Na+ blocked)
path of phototransduction
isomerization–>opsin–>transducin–>PDE–> takes cGMP to GMP–> results in hyperpolarization
Where is atRAL reduced to all trans retionol (atROL)
outter segment via NADPH all trans retinal specific dehydrogenase
this guy is a slave to photoreceptor regeneration
RPE
this guy transferes at ROL across the IPM
IRBP
which degernates first, cones or rods
rods, bc cones have alternate source of 11cRAL other then RPE
viagra has this and can interfere with basic phototransduction and lead to changes in rod and cone OS function
PDE5 inhibitors
light falling w/in receptive field of a neuron influences the activity of that neuron
every neuron that is higher order than the photoreceptor has a ‘field’ of photoreceptors that give it input
concentp of receptive field
All photoreceptors will ______ in reponse to light
hyperpolarize
when photoreceptors hyperpolarize they…
release less NT
Photoreceptrs are _____ cells because light hitting them turns them_____
OFF
OFF
when there is no light on a photreceptor it will
depolarize and release glutamate
Photoreceptors hyper and depolarize in a ______ fashion and relase NT’s in the same manner
graded
Photoreceptors do or do not produce action potentials
DO NOT!!!!
When a cone is depolarized it will release
glutamate (ig it’s excitatory, but not always)
Cones respond to light the same way, but single cone gives rise to
2 parallel pathways via connecting 2 dif bipolar cell types
The bipolar cell that is “ON” center
Light in it’s receptive field results in _____
and they have ______ synase with cone
cell depolarizing
sign reversing
On center bipolar cells have ______ contacts to coens
invaginating
On center bipolar cells act like a
classical inhibitory synapse
What will cause a hyperpolarizing effect on a ON center bipolar cell
glutamte that is released then the OFF center cell is in dark and depolarized
OFF center bipolar cell will ______ when light hits the center of our OFF center photoreceptor
hyperpolarize
The OFF center bipolar cell is considered _______ to the OFF center cone it synapses with
sign conserving
OFF center bipolar cells have _____ contact with OFF center photoreceptor
flat/basal
OFF center bipolar cells have _____ receptors
ionotropic
ON center bipolar cells ahve ______ receptor
metaborotropic
What is the point of parallel pathways
improved sensitivity
one provides info about stimuli that are brighter than background (ON-center) while the other provides info on stimuli dimmer then background (OFF-center)
Bipolar cells talk to
- Amacrine–for lateral connections
- Ganglion cells–to produce AP
- Parasol ganglions cells and midget ganglion cells
large cells w/ large receptive fields, more transient and project to magno layers (only 10%)
parasol cells
project to parvo layers, smaller cells w/ small receptive field and more sustained (make up 90%)
Midget ganglion cells
Two parallel bipolar cells connect to
like minded ganglion cell (sign-conserving)
Photoreceptors are completely synpaptically interconnected by an elaborate system of inhibitory interneurons called
horiozontal cells
these guys laterally interconnect cones with other cones
horizontal cells
every cone has a recipricol ______ synaptic relationship with all its neighbors
inhibitory
When a cone is excited (depolarized) it _____ horizontal cells it synpases with
excites
Excited horizontal cells will _______ neighbor cones via ______
inhibit
GABA
the action of a depolarized horizontal cells is to
hyperpolarize the cones it synapses with
The result of horiztonal cells is
enhanced edges
Lateral inhibition gives us
imporoved resolution: increaes our ability to recognize edges
Neurons responding to edge of a stimulus respond ______ then neurons responding to middle
more strongly
Edge neurons recieve inhibition from neighbros on only one side, the side____
away from edge
Neurons stimulated from the middle of a surface get:
inhibition from all sides
Light falling in the region surrounding the photoreceptor, but not directly on it, turns the photoreceptor
ON
What is our protein component of our rods
rhodopsin
Rhodopsin mutations will alter _____ fnx
rod
Rhodopsin mutations can
disrupt transport to OS, be retained in ER and affect stability of post-translation modification thus get constituitve activation
characterized by progressive loss of rod and cone receptors with accompying vision loss
Retinitis pigmentosum
Nighblindness is early symptoms with progressive constriction of visual field
RP
Inheritence of RP
X-linked autosomal dom or recessive
pigments that migrate from the RPE and adhere to blood vessels in RP will affect this first
rods
most common form of deaf/blindness
Usher
progressive vision/hearing loss, reduced odor identification, vestibular dysfuntion d/t motor proteins
Usher
Usher is dt defects in
sensory cilia, core of sterocilical
Congenital defects are \_\_\_\_ at birth same/worse though life can/cannot be classified easily affects one or both eyes equally
present at brith
same through life
can be classified
both eyes equal
visual aquity is often unaffected with confenital color vision defects: t/f
true
congenital vision affects males or females more
males
congentical color vision defects is usuallY;
protan or deutan
Aquired color vision: Onset\_\_\_\_ type and severity\_\_\_\_\_ \_\_\_\_\_ differences occur Visual acuity is \_\_\_\_\_\_ Predominately\_\_\_\_\_ affects males/females
after birth type and severity fluctuates Monocular diff occur (not both eyes same) reduced visual aquity predom tritan equal in male and female
Achromoatopsia causes defect in:
CNG-betta, CNGA-3, GNAT2 (transducin)
In achromatopsia cones:
cannot hyperpolarize in resposne to light
affected ind w/ achromatopsia have:
no cone function
