Chapter17 part4 p.581-586 Flashcards
Photons of _____ carry the least energy and have the _______ wavelength
red, longest
Our eyes are sensitive to wavelengths of
400-700nm
photons from __________ contains the most energy and have the ______ wavelength
violet, shortest
Both rods and cones contain special organic compounds called
visual pigments
pigments are located in each photoreceptor?s __________ segment, in flattened membranous plates called _________
outer, discs
Detection of light is called
photoreception
First step of photoreception
absorption of photons by visual pigment
visual pigments are derivateives of + what is it
rhodopsin- visual purple- visual pigment found in rods
rhodopsin conssits of a protein ______ bound to pigment _____ or _______, synthesized from ____________
opsin, retinal, retinene, vitaminA
All rods contain the ________ form of opsin
same
Describe the retinal pigment of cones
same retinal pigments as rods but retinal is attached to different forms of opsin
EAch type of cones have different form of ______
opsin
Cone population percentage of each cones
16% blue. 10% green, 74% red
New discs w/ visual pigments are continuously assembled at the base of the _________
outer segment of rods/cones
completed disc moves to
tip of outer segment
After about 10 days, the disc is shed in what
small droplet of cytoplasm
what cells absorb droplets with shed discs + what do they do?
pigment cells, they break down the disc membrane’s components and reconvert the retinal to vitaminA. The cells store vitaminA for later transfer to the photoreceptors
rhodopsin is broken down through
bleaching
Before retinal can recombine w/ opsin, it must be enzymatically converted from _________ form to ________ form
11-trans, 11-cis
The retinal conversion takes
energy/ATP, time
During bleaching, opsin is ___________ and _________ of cGMP ______
inactivated, breakdown, halts
When cGMP breakdown halts, how caan the Na gated channels reopen?
other enzymes in cytoplasm generate cGMP
body contains vitaminA reserve for __________
several months
Where is one reserve for vitaminA
pigmented part of retina
nyctalopia
night blindness- vitaminA deficiency
sodium entry through gated channels produce _______ (rods)
dark current
In the ________ of cGMP, Na channels are kept open
presence
cGMP is a derivative of
GTP
When the Na channels are open, the membrane potential is ______ whe the resting membrane potential is ________
-40mV, -70mV
When Na channels are open, the photoreceptor is continuously releasing __________ , specifically __________ . The inner segment continuously pumps _______ out
neurotransmitter, glutamate, Na ions
Normally, the retinal molecule is in the what form
curved 11-cis
when absorbing light, the retinal molecule changes into
more linear 11-trans form
the activated 11-trans opsin activated what + describe it
transducin- G protein
activated transducin activates what and describe its function
phosphodiesterase (PDE)- breaks down cGMP
when dark current is reduced, what happens in terms of neurotramsmitter
rate of neurotransmitter release declines
In active state of rod in light, what happens to Na ions?
active transport= export Na from cytoplasm
rod active state @ light what happens to membrane potential
drops toward -70mV, hyperpolarization
