sensory transduction and sensory receptors Flashcards
upon visual stimuli, does that cause a depolarization or hyperpolarization?
hyperpolarization
what is a typical cone-resting membrane potential?
-40 Mv
what are photopigments made up of
opsins and 11-cis retinal
whats makes each cone cell unique
diverse photopigment that responds to specific wavelength of light as a result of different AA sequence of opsin molecules
what type of molecule is opsin
protein molecule
what does 11-cis retinal get converted to upon activation from light
all-trans retinal
what G protein does opsin activate upon light stimulation?
transducin
what is this G protein made up of
alpha subunit, beta+gamma subunit with a GDP attached to the alpha subunit
what is the process of cone activation upon light stimulation
-upon light stimulation, the 11-cis retinal in the photopigment is converted to all trans retinal
This activates the opsin molecule
-this opsin will activate a G protein called transducin
The alpha subunit with the GDP attached will be exchanged for a GTP then this will break off and bind to PDE (CGMP phosphodiesterase)
-PDE has high rate of activity, converting CGMP to GMP
-This will cause the non-specific cation channels to close, as these channels require two CGMP molecules to open.
-the membrane potential will become more negative and cause hyperpolarization.
describe the 3 termination processes and one rebuilding process
-phosphorylation by rhodopsin kinase of opsin molecule, reducing its activity, which in turn will inactivate PDE, not G protein activation, as that alpha subunit won’t bind to PDE to activate it
-binding of arrestin to photopigment so it’s no longer active
-removal of retinal
-activation of guanylate cyclase that will rebuild cGMP
describe the resetting of this system
dephosphorylation of opsin
-removal of arresting
-attachment of new 11-cis retinal
describe the stimulus-response relationship involving light stimulation of photoreceptors
the greater the stimulus lead to greater response therefore greater hyperpolarisation, response is limited by reversal potential of specific ion (gets saturated)
what does a small dynamic range mean and its advantage
greater sensitivity, allows for fine-detail establishment
describe the differences between rods and cones
rods:
-have longer outer segment to capture as many photons as possible in the dark
-have prolonged responses to capture all photons possible
-rods have a limited supply of photopigment (saturate and become non-functional at light levels greater than twilight)
cones:
-have shorter outer segment as it is not as sensitive to light
-response terminated quickly to respond to changes in light
-have efficient adaptation by greater supply of photopigment (to respond rapidly to huge ranges of light levels)
explain why cones continually reset their resting membrane potential
to avoid saturation so that they reset the newly prolonged lit setting back to normal to respond to greater wavelength-ranges of light. it becomes adapted.
describe the biochemical adaptation in cones in immediate and persistent reduction in illumination
immediate:
-you get an immediate response as light in outer segment has decreased due to less photon being captured.
-the cones will depolarised due to decrease in illumination
-there will be an increase in cGMP level as PDE activity has been reduced while GC activity has increased
-this will increase number of channels open, allowing for calcium influx
persistent:
-there will be calcium influx due to opening of non-specific cation channels.
-calcium will reduce the activity of GC via binding to cGMP (gualylate cyclase activation protein)
-reducing the rate at which cGMP is made
-calcium also attahced to calmodulin, this will displace cGMP, closing the channels
-membrane potential will rest back at - 40mV.
-now it can respond to changes in both directions
-calcium slows down action of rhodopsin kinase by binding to recoverin, which means ospin can persist for longer, producing a bigger response
what are the two cells involved in photopigment regeneration? and which are used by cones and rods
retinal pigment epithelium (rods and cones) and muller cells (cones)
describe photopigment regeneration and include the unique enzyme that only cones have
all trans retinol gets converted to 11-cis retinal via the retinal pigment epithelium.
all trans retinol gets converted to 11-cis retinol via muller cells, which can get further converted to 11-cis retinal later by retinal converting enzyme (and only cones have this enzyme)
what are the two different types of receptor adaptations for inner hair cells
slow adaptation:
-tip link is anchored by myosin, which will bind with actin found within the cytoskeleton of stereocilia
-this controls tip-link tension and, hence, sensitivity
-increase tension increase sensitivity and respond rapidly
fast adaptation:
-controlled by calcium, which will enter via non-specific cation channels and attach to inside of channel, making it more likely to close
- so as stereocilia tilts, the calcium will enter and close channel
- helps remove stereocilia back up right again; this boosts oscillation and amplify the response.
what type of TRP thermoreceptor is involved with pain associated with high temperatures
TRPV1 at 45 degrees
what happens to this TRP thermoreceptors upon high damaging temperatures
this will change the shape of TRPV1 receptor within that temp range, causing cation channel to opnen,leads to depolarisation and signals to the brain that, this tissue is within this temp range
what effect does inflammation have on temp or heat sensation?
it will cause the threshold to be reduced, shifting the dynamic range to lower temperatures; therefore, if something isn’t hot, it will still feel hot
explain the process of injury evoked positive feedback between TRPV1 and inflammation
injury will cause release of protons and will also create an inflammatory response.
-leads to the production of inflammatory mediators
-the protons will bind to TRPV1 channels
-and inflammatory mediators will also attach to these channels or can generate second messages like kinases that can attach
-this makes the channel more likely to open
-this causes depolarisation via influx of Na and Ca
-leads to the release of proinflammatory peptides increasing this inflammatory response
-this nociceptor is hypersensitive
-there are mechs to terminate this but in some people it can go wrong, so even though the damage is healed they still remain in pain
