hd 220 takenote

hd 220 takenote - Tuesday I The Stimulus Light A Light is...

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Tuesday, March 04, 2008 I. The Stimulus: Light A. Light is electromagnetic energy that travels in waveform. B. Visible light only spans from wavelengths of 400-700 nm. C. We only have receptors for visible light. That is why we can’t see other types of electromagnetic energy, like infrared and ultraviolet. II. The Organ: Eye A. Light shines through the lens and the image is inverted at the back of the retina. B. The iris and pupil can expand or constrict to control the amount of light that enters the eye. C. The retina is covered with neurons whose axons go to the optical nerve (a cranial nerve). D. There are no photoreceptors at the convergence of the optic nerve on the retina because it’s composed of axons. This is the retinal blind spot. E. What we think is reality is what we perceive to be reality. 1. Dogs have a less complicated visual system but a very well developed olfactory system. This is opposite of humans. 2. Human brains and dog brains make species-specific sensory integrations. F. Visual problems due to the shape of the eye 1. In normal vision, the focal point of the lens lies on the retina. 2. In myopia (near-sightedness), the focal point is too short and does not reach the retina. 3. In hyperopia (far-sightedness), the focal point lies beyond the retina. G. Retina 1. The retina is located at the back of the eye. 2. There are photoreceptors called rods and cones on the retina. Photoreceptors turn light stimuli into neuronal signals. 3. The fovea is an area on the retina in which there are very few rods. There are more rods at the periphery of the fovea and more cones at the center of the fovea. III. The Receptor: Photoreceptors A. The retina’s photoreceptor’s convert light stimuli first into chemical signals, which cause a change in the membrane potentials of nearby neurons to create an electrical signal. B. Rods are responsive to motion and dim light. 1. We see in black and whit at nighttime because rods cannot see color and are most active in dim light. 2. Rods are more numerous than cones. C. Cones help us see color. 1. They are responsive to detail and bright color. 2. They are located mostly at the fovea so that we can see high in detail. 3. There are three types of cones. They respond to different wavelengths of light: blue, green, and red. 4. They are differentially distributed in the eye. There are less blue cones than red and green cones. D. Clinical Disorder: Color Blindness
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1. The most common form of colorblindness is red/green blindness. The person cannot differentiate between red and green because of an absence of either red or green cones. This is more common in males than females (5% males, 0.5% in females). 2. The genes that code for red and green receptors lie close to each other on the X chromosome. This is an X-linked gene disorder that affects males because males only have one X-chromosome, thus one mutated X-chromosome manifests in the color-blind phenotype. Females have two X-chromosomes, which means they need two mutated X-
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hd 220 takenote - Tuesday I The Stimulus Light A Light is...

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