Textbook Notes (363,381)
Canada (158,358)
Neuroscience (289)
NROC64H3 (81)
Niemier (23)
Chapter 9


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University of Toronto Scarborough

INTRODUCTIONLight is electromagnetic energy that is emitted in the form of wavesThe 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 activityThe output of the retina is not a reproduction of the intensity of the light falling on it but is specialized to detect differences in the intensity of light falling on different parts of itThe 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 rememberedPROPERTIES OF LIGHT Light Electromagnetic radiationWavelength the distance between successive peaks or troughsFrequency the number of waves per secondAmplitude 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 content 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 92Hot 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 rayReflection 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 90Absorption 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 blueRefraction 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 EyePupil the opening that allows light to enter the eye and reach the retina It appears dark due to the lightabsorbing pigments in the retina
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