Ch. 7 Thermo and Vision Flashcards
thermoreceptors in facial pits of rattlesnakes
infrared detectors that detect change in tissue temp
increase firing rate transiently when temp changes by .002 degrees C to modify behavior
helps snake hunt in poor light
thermoreceptors
specialized nerve endings in the skin
two types of thermoreceptors in the skin and tongue
some increase firing when hot
some increase firing when cold
both have less firing at sustained temp
photoreceptors
transduce photons of light into electrical signals interpreted by the nervous system
rhodopsin
visual pigment containing the light-absorbing retinal and protein opsin
lens
structure that refracts (bends) light
compound eyes of arthropods
image-forming containing many units called ommatidium aimed at a different part of the visual field
each ommatidium of a compound eye contains several ____________ cells
photoreceptor
rhabdomere
part of the cell where the plasmam membrane has densely packed microvilli
increases chance light will be captured b/c high surface area
rhabdome
12 rhabdomeres that surround the dendrite of an afferent neuron
how does vertebrate eye work
light is bent through the cornea and bent again to form an inverted image on the retina
accomodation
adjusting the lens to see
ability decreases in old age
the stimulud for all photoreceptor cells is __________ ________ that falls within a range of energy called visible light
electromagnetic radiation
violet (400nm) is highest energy light and red (650-700nm) is lowest energy
where are the photoreceptors that transduce light energy found
retina
rods vs cones
rods are blk/white and function in dim light
cones are color and function in bright light
fovea
part of the retina that provides a lot of info - high visual acuity
only have cones
vertebrate rods and cones _________ in response to light simuli, whereas invertebrate rhabdomeres ________
hyperpolarize, depolarize
light for vertebrates ________ permeability of Na across the outer membrane
decreases
in the dark, the Vrest of the vertebrate rod is…
much less inside-negative than normal neurons
Na channels are always open and Na is coming in but is being pumped out by the Na/K pump
do rods and cones make APs
no, they release nt
what does a light induced decrease in dark current do
makes Vm in outer segment hyperpol toward Ek which spreads to inner segment
this causes nt release
________ of photoreceptors decreases amount of nt released
hyperpolarization
all visual pigments contain 2 things
a protein opsin
a light absorbing molecule retinal
retinal 2 different states
no light = linked to opsin in a cis
light captures = trans
activated rhodopsin (light)
activates the G protein transducin –> activate phosphodiesterase (PDE) –> turn cGMP to GMP
this closes cGMP-gated channels and the cell hyperpolarizes
when light stimulus ends, cGMP…
is regenerated by guanylate cyclate and dark-current channels reopen
visual _______ is best when the image is focused onto rods and visual ______ is best when the image is focused onto the cones of the fovea
sensitivity, acuity
thermal energy equation
Etherm = kT
k is boltzman’s constant
T in K
what does thermal energy do to vision
lowers sensitivity of receptors b/c it produces a constant “background noise”
equation for energy of a single photon
E = hv = hc/lamda
h = planck’s constant
v = frequency
c = speed of light
lamda = wavelength
synesthesia
1 input generates multiple responses
ex. see a color and get taste
optogenetics
light sensitive algae protein channel that opens to blue light
clone gene of channel proteins and transfect into a neuron
neuron becomes light sensitive and is activated by flashing light
neuron specific promoters
promoter attached to a light-sensitive channel gene
Put into virus into brain so expressed in target neurons
target disease or memory
advantages of light sensitive neurons
precise activation by illumination
cell-specific/region specific expression
speed of control is fast: speed of light
target specific pathways
No metabolic side effects
