BIO 365R EXAM 3 CLASS NOTES

BIO 365R EXAM 3 CLASS NOTES - LECTURE 21 Last time The Eye...

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LECTURE 21 04/08/08 Last time.. - The Eye allows us to convert images from environment (focus using adjustable lens) retina   light-sensitive layer; cells that are most sensitive to light (convert  light to electrical signal) are located in the innermost area of the retina  (farthest from light - must traverse other cells) cones & rods o the eye needs to operate under a broad range of condition levels (very  dark/low light   very bright) o enabled by 2 visual systems: rods – in dim light; too sensitive to bright light (get totally  saturated);  cone – not sensitive enough; bright light outer segment of rods – internal disks (inside membrane of cell);  packed with photopigment (rhodopsin); location of conversion of  light into electrical signals folds in membranes in cones o no AP graded potential constantly releasing neurotransmitter rate of release depends on amount of light output cells – send signal to thalamus rods have single type of photopigment – 1 sensitivity to light  across the wavelength; colorblind; short wavelengths (400 nm) cones are sensitive to 3 types of wavelength of light (3 types of  pigments) – 496, 531, 559 nm relativity of 3 cone types that carry information about color must carry high resolution information
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o need fine details o need high resolution system o need to be able to cover a broad range o fovea o constantly moving high resolution of high portion of our eye from 1  object to next to get the illusion of having high resolution everywhere o density of photoreceptor in our eyes   # of photoreceptors/millimeter  sq fovea = 0 everything else measured relative to fovea # of rods (density) drops as you move away from fovea because  the cones become larger optic disk   light-sensitive layer is innermost layer; axon is  outermost layer; in order for axons to leave the eye, they have  to cross the area of the eye closest to eye (so you get a  blindspot) o must have small & dense receptors to get very high resolution  information photoreceptor density o only in fovea o as we move away from the fovea cone size  blind spot region o ganglion cells have axons on the outer-side & get out of the eye  (where they leave the eye, no photoreceptors) o vision is actually a construct by our brain and different from what our  eye is sending to us - how photoreceptors convert information about light into electrical signals electrode into photoreceptor cell   find that in the dark, the cells are fairly  depolarized (-40 mV) o  shine light for a brief period (ms), the cells hyperpolarize (-65 mV) o more light, more hyperpolarized
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