tailieunhanh - Lecture Human anatomy and physiology - Chapter 15: The special senses (part b)

In this chapter, students will be able to understand: Describe the events involved in the stimulation of photoreceptors by light, and compare and contrast the roles of rods and cones in vision; compare and contrast light and dark adaptation; trace the visual pathway to the visual cortex, and briefly describe the steps in visual processing. | 15 The Special Senses: Part B Light Our eyes respond to visible light, a small portion of the electromagnetic spectrum Light: packets of energy called photons (quanta) that travel in a wavelike fashion Rods and cones respond to different wavelengths of the visible spectrum Figure Wavelength (nm) Visible light (b) (a) Blue cones (420 nm) Rods (500 nm) Green cones (530 nm) Red cones (560 nm) X rays UV Infrared Micro- waves Radio waves Gamma rays Light absorption (pervent of maximum) Refraction and Lenses Refraction Bending of a light ray due to change in speed when light passes from one transparent medium to another Occurs when light meets the surface of a different medium at an oblique angle Refraction and Lenses Light passing through a convex lens (as in the eye) is bent so that the rays converge at a focal point The image formed at the focal point is upside-down and reversed right to left Figure Point sources (a) Focusing of two points of light. (b) The image is inverted—upside down and reversed. Focal points Focusing Light on the Retina Pathway of light entering the eye: cornea, aqueous humor, lens, vitreous humor, neural layer of retina, photoreceptors Light is refracted At the cornea Entering the lens Leaving the lens Change in lens curvature allows for fine focusing of an image Focusing for Distant Vision Light rays from distant objects are nearly parallel at the eye and need little refraction beyond what occurs in the at-rest eye Far point of vision: the distance beyond which no change in lens shape is needed for focusing; 20 feet for emmetropic (normal) eye Ciliary muscles are relaxed Lens is stretched flat by tension in the ciliary zonule Figure Lens Inverted image Ciliary zonule Ciliary muscle Nearly parallel rays from distant object (a) Lens is flattened for distant vision. Sympathetic input relaxes the ciliary muscle, tightening the ciliary zonule, and flattening the lens. Sympathetic activation Focusing for Close Vision Light from a | 15 The Special Senses: Part B Light Our eyes respond to visible light, a small portion of the electromagnetic spectrum Light: packets of energy called photons (quanta) that travel in a wavelike fashion Rods and cones respond to different wavelengths of the visible spectrum Figure Wavelength (nm) Visible light (b) (a) Blue cones (420 nm) Rods (500 nm) Green cones (530 nm) Red cones (560 nm) X rays UV Infrared Micro- waves Radio waves Gamma rays Light absorption (pervent of maximum) Refraction and Lenses Refraction Bending of a light ray due to change in speed when light passes from one transparent medium to another Occurs when light meets the surface of a different medium at an oblique angle Refraction and Lenses Light passing through a convex lens (as in the eye) is bent so that the rays converge at a focal point The image formed at the focal point is upside-down and reversed right to left Figure Point sources (a) Focusing of two points of light. (b) The image is .

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