Textbook Notes (368,326)
Canada (161,799)
Neuroscience (289)
NROC64H3 (81)
Chapter 9

chapter 9

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Matthias Niemeier

INTRODUCTION y Light is electromagnetic energy that is emitted in the form of waves y The visual system begins with the eyes At the back of the eye is the retina which contains photoreceptors specialized to covert light energy into neural activity y The output of the retina is not a reproduction of the intensity of the light falling on it but isspecialized to detect differences in the intensity of light falling on different parts of ity The first synaptic relay in the pathway that serves visual perception occurs in a cell group of the dorsal thalamus called the lateral geniculate nucleus LGN From the LGN visual information ascends to the cerebral cortex where it is interpreted and remembered PROPERTIES OF LIGHTLight Electromagnetic radiation y Wavelength the distance between successive peaks or troughs y Frequency the number of waves per second y Amplitude the difference between wave trough and peak The energy content of electromagnetic radiation is proportional to its frequency ie high frequency short wavelengths has the highest energy contenty Only a small part of the electromagnetic spectrum is detectable by our visual system This visible light consists of wavelengths of 400700 nm see Fig 92 y Hot colours eg red or orange have long wavelength light and less energy than cool colours eg blue or violet Optics In a vacuum a wave of electromagnetic radiation will travel in a straight line This is a ray y Reflection the bouncing of light rays off a surface This depends on the angle at which it strikes the surfaceA ray striking a mirror perpendicularly is reflected 180 back upon itself and a ray striking a mirror at 45 angle is reflected 90 y Absorption the transfer of light energy to a particle or surface Black surfaces absorb the energy of all visible wavelengths Some absorb light energy only in a limited range of wavelengths and reflect the remaining wavelengths For example a blue pigment absorbs long wavelengths but reflects a range of short wavelengths centered on 430 nm that are perceived as blue y Refraction the bending of light rays that occur when they travel from one transparent medium to another It occurs because the speed of light differs in two media eg light passes through air more rapidly than through water The greater the difference between the speeds of lights in the two media the greater the angle of refraction see Fig 93THE STRUCTURE OF THE EYE Gross Anatomy of the EyeIt appears dark y Pupil the opening that allows light to enter the eye and reach the retinadue to the lightabsorbing pigments in the retina
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