13618570
Description
Flashcards by J yadonknow, updated more than 1 year ago
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Created by J yadonknow
over 6 years ago
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| Question | Answer |
| Photoreceptors are | Cells that absorb light |
| Invertebrate / verterbrate photoreceptors | Retinula cells Rods and Cones |
| Retinula cells | Have rhabdomere formed by Mv Light depolarises the cell |
| Rods and Cones | Opsin molecules stacks of modified cillia Light hyperpolarises the cell |
| Eye diagram | Cornea lens optic disc retina |
| Where are photoreceptors found/ | In retina |
| Rod / cone diagram | Outer segment of modified cilium inner segment synaptic terminals |
| Comparing structure and function | Cones have shorter stacks, less opsin, less light sensitive Rods more discs = more opsin = remain active even at low level light |
| Vertebrate phototransduction in the dark | Na+ and Ca++ channels kept open by high cGMP PhotoR depolarises Transmitter released RECEPTOR ITSELF DOESN'T GENERATE AP |
| Vertebrate phototransduction in light | Light activates transducin to break cGMP to GMP Ion channels close, hyperpolarising the cell and reducing transmitter release |
| What are the 4 classes of photoR in humans? | Red/green/blue cones and rods |
| How would you compare their absorbance on a graph? | Relative absorbance (%) against wavelength (nm) |
| What colour don't rods absorb? | red |
| Show the visual pathway of light sensing in humans | Sensory R in retina Gnaglion cells synapse to thalamic nucleus Thalamic cell geos direct to 1' visual cortex Cross-over at optic chiasma |
| Where is colour processed in the 1' visual cortex? | V4 |
| Where are dynamic movements processed? | V5 |
| Visual processing in lower vertebrates | Reptiles, amphibians, and fish have rudimentary forebrains Reflex movement is processed in the optic tectum (midbrain) |
| Bird visual acuity | visual acuity in medial forea (side vision) is x2/3 that of humans |
| Invertebrate phototransduction in light | Light + in opsin, + PLC -> PIP2 -> DAG + IP3 This opens ion channels in membrane causing the photorecetor to depolarise and release histamine, but don't generate AP |
| What are compound eyes made up of? | Photor, each with its own lens and colour cartridge |
| What is the cartridge known as? | Ommatidium |
| Diagram of ommatidium | Photor1-8 rhabdomeres pigment cells lens |
| What is special about compound eyes? | Can absorb light from all polarisation |
| Which rhabdomere have differing microvilli directions and why? | Outer 1-6, light from all directions sensed |
| Which rhabdomere are sensitive to polarisation? | 7/8 |
| Why do insects have this? | Because light is polarised in concentric circles around the sun so this aids navigation |
| Simple eyes | Ocelli |
| Use in flying insects | Triad of ocelli for horizon detection |
| What are the eyes of octopi and vertebrates an example of? | Convergent evolution |
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