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, forexample 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. Visual system works on reflected light. Atmosphere is 60 miles of gas protecting us from sun's short wavelengths - 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 bouncedoff 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 retinalcell 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 feedthe 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 ofcones making it where we see fine detail best but we need a ton of light. The peripheries ofour 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
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