Lecture10_vision1 - Phototransduction Phototransduction may...

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Phototransduction Phototransduction may be broadly defined as the conversion of electromagnetic energy (such as light) into some other form of energy In neuroscience, phototransduction refers more specifically to the transduction of light energy into neural signals, which is the first step in visual perception Phototransduction is performed by a specialized sensory organ at the back of the eye, called the retina , which translates visual images into the language of actions potentials Action Potentials To brain
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The Electromagnetic Spectrum 700 nm 550 nm 400 nm Light is made of very tiny particles (or “quanta’) called photons which travel at the speed of light: ~186,000 miles/sec ( waaaay faster than sound!) Photons are particles of electro-magnetic energy which are emitted from a radiant energy source Photons have wave-like properties; free photons travel in bumpy ripples called wave packets The distance between peaks and valleys of a photon’s ripples is called its wavelength A photon’s wavelength determines the color of its light (red longest, blue shortest) Wave Packets Visible light spans just a tiny fraction of the electromagnetic spectrum, between 400-700 nm
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How do photons get into your eyes? The reason we can see the world around us is because it is filled with objects that reflect photons into our eyes When photons from a broad spectrum light source (such as the sun, or a light bulb, which generate many photons of all colors) bounce off of an object, the reflected photons enter our eyes, which allows us to see the object Most objects absorb some wavelengths of light, while reflecting other wavelengths. This is what gives them their color. For example, an apple reflects only red photons into our eyes, while absorbing photons of all other wavelengths, which is why the apple it looks red! Light from the sun contains photons of all wavelengths, but only red photons bounce off the apple
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The Eye: A Camera in your head Light enters the front of the eye by passing through its transparent outer layer, called the cornea, and then through a hole called the pupil The iris (which is the colored part of the eye) controls how much light enters by adjusting pupil size The lens focuses light on the retina at the back of the eye Ciliary muscles distort the shape of the lens to focus objects at different viewing distances onto the retina The retinal image is flipped upside-down and right-to-left on the back of the eye!
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The Retina: A tiny TV screen at the back of your eye! A TV screen (or computer screen) is made up of thousands of tiny dots called “pixels” When you look at the entire screen from a distance, the pattern of pixels forms the image you see on the screen When you magnify the screen and look very close up, you see the individual pixel dots Your retina is like a tiny TV screen: it is made of many tiny light detectors that act like the pixels of a TV screen to form an image What are pixels in the retina made of?
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