Lecture 6- Hypothalamus Flashcards
what’s the most reliable method of telling time of day?
light
what are the 2 main types of photoreceptor?
rods and cones
at which light levels are rods most effective?
dark
at which light levels are cones most effective?
light
how do photoreceptors adapt?
- in the dark, there’s an influx if cations (Na+/Ca2+)
- Calcium inhibits GCAP- a molecule that catalyses GTP to cGMP
- In the dark therefore cGMP is low (calcium influxes more, so inhibits GCAP from making cGMP)
- In the light there’s a reduced EC Ca2+ (less influx) and an increased cGMP production so cGMP-gated channels open
under dark adapted conditions, what does relatively dim light drive?
full hyperpolarisation
under light adapted conditions, what does relatively bright light drive?
only partial depolarisation (unless it’s super bright)
what does photoreceptor adaptation allow?
receptors can detect changes in light intensity over space and time under all lighting conditions
why is it important to regulate how bright our environment is? (2)
- to regulate pupil size
- tell time of day (for circadian rhythm)
describe the mimosa plant’s circadian rhythm
- wilts at night
- has an internal circadian clock that’s set by local time from sun light
- it will continue to show 24 hr variation cycles even in total darkness- endogenous clock
how do we know that rods and cones aren’t the only photoreceptors?
many non-mammals detect light w/o them
mice have shown pupillary response to light when completely blind
what’s the known extraretinal photoreceptor?
retinal ganglion cells- depolarise in response to light
where do retinal ganglion cells project?
to the thalamus
what is melanopsin?
protein found in retinal ganglion cells
why do we know melanopsin is necessary for photoreception?
lack of photoreception in melanopsin KOs
