EXP3202 FINAL STUDY GUIDE Light is a form of electromagnetic radiation which is a vast spectrum Light falls into the electromagnetic radiation spectrum between ultraviolet infrared 400 700 nm Short wavelength electromagnetic radiation is dangerous to us because the shorter the wavelength the higher the energy They re ionizing can change structure of things like mutate your cells give you cancer Long wavelengths are safe Wavelengths we see as Light 400 700 nm The combinations of sensitivities of the 3 types of cones gives us our overall ability to detect these wavelengths Photons light wavelength color number brightness Since light comes in packets we have a limited capacity to absorb The eye must continuously regulate regenerate Photoreceptors a light sensitive receptor in the back of the retina When photoreceptors sense light they can stimulate bipolar horizontal amacrine cells which leads to the ganglion cells Functional differences between rods and cones rods 1 1 connection cones many 1 connection are two types of photoreceptors that differ in sensitivity to light the threshold curves are inverted absorbance curves Rods are most sensitive to green light 510 nm The amount of light required for cone photopic vision is generally too much light for rod scotopic vision Our eyes adapt to the darkness and brightness for example if you leave a dark area and go into a bright one your pupil constricts and you will probably sneeze Rods are recovering their ability to absorb light which takes about 15 minutes Adaptation to light is much faster because there s not enough light when it s dark so when it s light rods already ready When you have more light entering your eye than can be absorbed you re blind The basic structure and function of the human eye retina retina a light sensitive membrane in the back of the eye that contains rods cones which receive an image from the lens send it to the brain through the optic nerve Iris colored part consists of a muscular diaphragm surrounding the pupil regulates the light entering the eye by expanding or contracting the pupil Pupil dark circular opening at the center of the iris in the eye where light enters the eye Cornea the transparent window into the eyeball most light photons are transmitted through it rather than being reflected or absorbed It forces the eye to close to produce tears if the cornea is scratched Crystalline lens lens inside the eye that enables the changing of focus Like the cornea it has no blood supply so it s transparent and both the lens cornea are curved optical elements Vitreous humor transparent fluid that fills the vitreous chamber in the posterior part of the eye it refracts light Macula back inner surface of eye directly behind iris lens it s an anatomical location Fovea inside the macula We are special in having a fovea seeing sclera the white part of the eye means you have a fovea The iris lens are the only moving parts The function of curved optical elements of the eye cornea lens create a microscope in reverse The purpose of curve is to alter the projection of the photons that have bounced off the object push inward refraction Because of this reversal flip that s why there s left right crossing When you re looking at an object up close you need more curvature to see better because there is more refraction When you look at things far then it gets more flat Eyeglasses contact lenses correct variations in the structure of the eye Emmetropia condition in which there is no refractive error because the power of the eye is perfectly matched to the length of the eyeball Myopia nearsightedness a common condition in which light entering the eye is focused in front of the retina distant objects can t be seen sharply Hyperopia farsightedness common condition in which light entering the eye is focused behind the retina accommodation is required in order to see near objects clearly Astigmatism visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye usually the cornea Photoreceptor rods cones a light sensitive receptor in the retina Bipolar cell a retinal cell that synapses with either rods or cones not both with horizontal cells then passes the signals on to ganglion cells Ganglion cell a retinal cell that receives visual information from photoreceptors via 2 intermediate neuron types bipolar amacrine cells transmits information to the brain midbrain Light first hits ganglion cells then bipolar cells finally photoreceptors The Blind Spots you normally don t notice because your visual system fills it in with information from the surrounding area The optic disk is where the arteries veins hat feed the retina enter the eye where the ganglion cells axons leave via the optic nerve This portion of the retina contains no photoreceptors At night we have 2 blind spots because there s very few rods working directly in the middle of the fovea Fovea vs Periphery of the human retina the fovea contains the highest concentration of cones making it where we see fine detail best but we need a ton of light The peripheries of our retina have a higher concentration of rods and very low concentration of cones making it have a low threshold for light but unable to see fine detail We have cones mainly in fovea rods elsewhere Since cones have specific small area that can see we need to be able to move it look specifically at things The trade off between identification detection is expressed in our eye via rods and cones Acuity ID is with cones sensitivity to light detection is with rods Phototransduction occurs within rods cones They re the only cells that can transduce light into neural activity which occurs in the outer segments That s where stacks of disks are each disk represents a unit of light absorbing capacity Light closes the NA channels Light inhibits photoreceptors darkness excites There are always fresh discs in the outer segment of photoreceptors as top ones are shed They absorb light photons carry out phototransduction Each disk has metabotropic receptors They have second messenger systems g protein coupled receptors The end result is similar to 1st messenger systems Visual pigments are metabotropic receptors Photoreceptor responses to light vs ganglion Cells are interested in contrast they don t care about light Opponent process many 200 photoreceptors rods connect to one retinal ganglion cell This allows for edge enhancements What leaves the eye are dots of contrast light dark or 2 color
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