Sensory systems 6 - Non visual photoreceptors

Tell time of day, predict the changes in the environment. They are for survival purposes, circadian rhythms
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Tell time of day, predict the changes in the environment. They are for survival purposes, circadian rhythms
Key functions of non-visual photoreceptors
life is characterised and evolved around the 24hr clock and variations in the biological environment. If it wasn't they may not survive. E.g., go out at night more and be at risk of predators.
Importance of none-visual photoreceptors in terms of night and day
study done in the 1800s. The rotation study, the plant detects light at daytime and opens it's leave. but even when dark and left in cupboard they would still open their leaves at a certain time. This showed there must be another function for keeping in time and in tune not just daylight as the only mechanism. - important findings in terms of circadian rhythms
What is the mimosa plant study?
The differences in ambient illuminations, dawn to dusk can have a difference of billion times higher luminance at mid day.
How do biological clocks sync to local times?
Study of mammals and circadian rhythms. Looked at nocturnal animals that run on a wheel at night. always has separate inactive and active zones. They would always get up at a certain time, when lights were off at 8pm. When they moved the around the mouse would adjust to waking when the lights went off. This showed that they had a endogenous timing mechanism which was synchronised to the light dark timing.
Describe and explain the monitoring rodent locomotor activity study...
In part of the hypothalamus called the superchiasmatic nuclei which is located just after the optic chiasm.
Where are circadian rhythms generated?
Some fibres deliver info to retina and others deliver information to other parts of the brain....
where is information delivered to from the superchiasmatic nuclei?
The activation of rods and cones receptors at different times. How activated each set is. Rods more sensitive to different light intensities - depolarise when light, hyperpolarised in the dark. Cones work better in the dark, they have to adjust sensitivities during the day - photoreceptor adaptation. High intensity changes across dawn and dusk.
How do we measure background light intensity?
it is the end product of photoreception. When light levels are low there is less cGMP production. In higher light levels the channels are open and then eventually inhibited by calcium ions which helps bring hyperpolarisation back to normal.
What is the function of cGAMp in light reception?
Changes the relationship between light intensity and photoreception so cones can monitor the different ranges of light. Cones can not tell information about absolute light intensity rather the changes across a range. It is different in mammals and non-mammals
What are the properties of photoreceptor adaptation? why is it important?
Non-mammals often have photoreceptors outside of their eyes - Experiment on birds in the 1960How does non- mammalian photoreceptor adaptation work?Looks at house sparrows. These birds exhibit a behaviour whereby they jump between porches in the day. They were first kept in the dark for 15 days - they found the sparrows still woke but were waking up later each day. When the light is switched on it hops between purches but only when the lights are on. They then tested this behaviour in birds with their eyes removed and found the same behaviours were exhibited. - this showed they must have photoreceptors outside of their eyes. Injected with C.B - light unable to get into brain via the skin - biological tissue is permeable to light - black ink injection.Describe and explain the 1960 house sparrow experiment. (looks at how non mammals respond to and monitor different light intensities)With no eyes there is no ability to adjust to photoreception. Loss of eyes - all loss of ability to sync to times.Photoadaptation in mammals...they generated an animal which did not have rods or cones and their prediction was that they wouldn't have any light reception. owever - they do have a response to light still. Light response not coming from rod or cone They have the same behaviour in the light dark cycle with running on their wheels. When lights change, they wake up earlier day by day. This is the same in people who are blind...How did scientists deduce if rod and cone receptors were the origin of all light signals?... Retinal ganglion cells. They injected dye into the SCN of rats and were able to label a small number of ganglion cells sending information to the circadian clock. They also followed this up with electrophysiological recordings. On type retinal ganglion cells- a certain type of ganglion cell still respond directly to light signal when separates.What was found as another photoreceptor?Even without cone or rod receptor cells the mice/rats pupil would dilate in response to light.What other evidence was there that there was another type of cell involved in photoreception?They are of the opsin family which is sensitive to photons of light. The opsin amino acids shared rod cone family. They are membrane bound and therefore can bind 11-cis retinal, therefore g-coupled receptors. Different opsins in different mammals.How do non-rod or cone receptors detect light?in Retinal ganglion cells that project to hypothalamus Blue dye - circadian clock. Example is melanopsin knockout mice. No melanopsin - no response to light Yes do have melanopsin - respond to light. It is a light activated G-coupled receptor. which has the same function as the photoreception cascade and 11-cis to retinaldehydeMelanopsin