Light Detection In Animals Flashcards
What is photo reception and light?
Photoreception is the conversion of electromagnetic waves to nerve signals
Colour is not a property of light, or of objects reflecting light; it is a sensation generated by the brain
Difference between compound eyes and vertebrate eye?
Light and photo-reception occur in the same direction in compound eyes whereas in the vertebrate it is anti parallel.
Two major photoreceptors types and which is most sensitive?
There are two major photoreceptor types, those based on cilia and those based on microvilli.
With the exception of rods in vertebrates, microvillar photoreceptors are the more sensitive, capable of converting the energy of a single photon into a detectible receptor current.
How is transduction triggered in microvillar photoreceptor?
Light hit rhodopsin which activates it. This triggers a cascade of reactions via G protein coupled receptors involving IP3 and DAG that open calcium channels and allows influx from submicrovillar cisternae to microvilli.
Sodium also influxes from this pathway.
How is photo-transduction processed in the vertebrate rod?
Light hits rhodopsin and activates it caused a cascade via G protein couples receptors involving cGMP to GMP and calcium and sodium channel closer.
Channels open in dark, closed in the light. Opposite of microvillar photoreceptor of fly.
How many cone pigments did the common ancestor of birds and mammals have?
4 cone pigments. Birds retained all of them. 2 cones believed to be lost in early mammals. 3rd cone pigments in reclaimed through mutation in primates and humans. 3rd cone is diff to what birds have though.
Birds have superior vision.
What organism has the highest amount of photoreceptor?
Mantis shrimp have 16 types of photoreceptor. Can see a very wide UV range. Have UV1 and UV2 opsins.
Mycosporine-like amino acid (MAA) pigments in the crystalline cones function as UV-specific spectral filters to tune the photoreceptors to specific wavelengths. Can sense polarised light.
How are animals such as mammal carnivores, rodents and Cetacea adapted for scoptopic (low-light) vision?
They have a tapetum luicidum. A layer of cells between the retina and the choroid containing refractive crystals.
Also converging photoreceptors and more opsin. Amplifies signal in low light.
How are insects adapted to scotopic (low-light) vision?
They have scotopic omatidia. Similar to photopic omatida but instead have a clear zone between crystal cone and reticular cell with a crystalline tract.
Scotopic omatidia of nocturnal insects have pigment in the secondary pigment cells that can contract to allow light to excite photoreceptors in nearby omatidia at night.
