Lecture 11.F10

Lecture 11.F10 - Neuroscience 106: Lecture 11 - The Retina,...

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Neuroscience 106: Lecture 11 - The Retina, continued Assignment : In Bear et al. study Chapters 9 and 10. TODAY'S LECTURE: The Visual System (cont.) I. Rods versus Cones A. Rods contain rhodopsin and are more light sensitive than cones (a single photon of light may be detectable by rods but not by cones). 1. One reason for this is that the process of signal amplification is greater in rods. 2. Cones have coneopsin instead of rhodopsin. a. There are three different types of coneopsin: red, green, and blue. Meaning that they are most sensitive to light in the red, or green or blue wavelengths. b. The difference between the three forms of coneopsin is small. The difference is a small change in the amino acid sequence allowing for maximal sensitivity to different wavelengths of light. As an interesting tidbit, there are 2 versions of the red coneopsin gene in men and these produce red opsins that vary by a single amino acid. This difference results in the two red coneopsins being maximally sensitive to slightly different wavelengths of red light. Thus, men with different versions of this opsin do not perceive the same thing when they see a red object. This answers the philosophical question about whether different people see objects, colors etc. in the same way. They don't. 3. Another reason that rods are more sensitive to light is that the outer segment of rods is larger; therefore they have a larger surface area to absorb light. 4. Rods also have more photopigment densely packed into the membrane of the optic disks, so they absorb more light. B. In bright light the photopigment in rods (but not cones) is saturated (bleached). Therefore rods aren't functional in bright light, while cones are. 1. This means that we have two parallel visual systems , one for bright light and one for very dim light. 1
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2. At night colors appear to be muted. But the same spectral frequencies exist in bright and dim light. The reason we don’t perceive colors in dim light is that cones don't work in dim light , so we don’t perceive color because we’re using a part of the visual system that is color blind. II. Receptive fields of cells A. How do RGCs code information that results in perception of the visual stimulus? B. Below is a diagram exemplifying receptive fields of RGCs : 1. A neuron’s receptive field is the location in the environment (or the surface of the body) from which an appropriate stimulus will change that cell's activity. The term
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This note was uploaded on 11/10/2010 for the course CBNS 106 taught by Professor Korzus during the Fall '08 term at UC Riverside.

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Lecture 11.F10 - Neuroscience 106: Lecture 11 - The Retina,...

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