Hearing Hearing is the ability to sense sound which consists of waves of

Hearing hearing is the ability to sense sound which

This preview shows page 176 - 179 out of 215 pages.

Hearing Hearing is the ability to sense sound, which consists of waves of pressure in air or water The frequency of the sound is the number of pressure waves that occur in one second (measured in Hz) Differences in sound frequency are perceived as different pitches Human range is approximately 20 Hz to 20 KHz Virtually all animal pressure-sensing systems are based on the same mechanism, a mechanoreceptor cell that responds to pressure The Mammalian Ear The ear transduces sound waves into action potentials and sends the information to the brain There are three parts to the ear: The outer-ear collects pressure waves and funnels them into the ear canal where they strike the tympanic membrane The middle ear amplifies sound waves enough to stimulate the hair cells within the cochlea of the inner ear The inner ear detects sound frequencies The fluid inside the cochlea vibrates, stimulating certain hair cells Each is separated from the others by a membrane Mammals have an outer ear, middle ear, and inner ear The outer-ear collects incoming pressure waves and funnels them into the ear canal The sound waves strike the tympanic membrane in the middle ear
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Vibrations are then passed to the ossicles (three small bones) The stapes vibrates against the oval window and generate waves in the fluid of the cochlea Hair cells detect these waves The cochlea detects sound frequencies It is divided into three fluid-filled chambers separated by membranes Hair cells form rows in the middle chamber The bottom of each hair cell connects to the basilar membrane The stereocilia also touch the tectorial membrane Hair cells in certain places on the membrane respond to different frequencies
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The basilar membrane varies in stiffness Different parts of the basilar membrane vibrate in response to different sound frequencies and result in the bending of hair stereocilia In this way, hair cells in a particular place on the membrane respond to sounds of a certain frequency Photoreception The organs involved range from simple, light-sensitive eyespots to more complex image- forming eyes A species’ sensory abilities correlate with the environment it lives in and its mode of life Cave dwellers may have no functional eye Insects have compound eyes Vertebrates have a simple eye A structure that has a lens that focuses incoming light onto a layer of receptor cells The Vertebrate Eye Sclera The outermost layer of tough white tissue Cornea The front of the sclera forms this transparent sheet of CT, which helps focus light on the retina Iris Pigmented round muscle that contracts or expands to control the amount of light entering the eye Pupil The hole in the center of the eye Retina Comprised of three distinct The simple eye Light enters the eye through the cornea, passes through the pupil, and strikes a curved, clear lens
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