Hearing

By: Melba ReyesBy: Melba Reyes

Sound Sound is a series of Sound is a series of

compression waves that moves compression waves that moves through the air or other material through the air or other material created by the vibration of created by the vibration of some object some object

The speed or velocity of sound The speed or velocity of sound in air is approximately 344 in air is approximately 344 meters/second, 1130 feet/sec. or meters/second, 1130 feet/sec. or 770 miles per hour at room 770 miles per hour at room temperature of 20temperature of 20ooC (70C (70ooF). F). The speed varies with the The speed varies with the temperature of air, so sound temperature of air, so sound travels slower at higher travels slower at higher altitudes or on cold days.altitudes or on cold days.

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Sound Whenever an object in air vibrates, it causes compression Whenever an object in air vibrates, it causes compression

waves in the air. These waves move away from the object waves in the air. These waves move away from the object as sound. There are many forms of the vibration, some not as sound. There are many forms of the vibration, some not so obvious.so obvious.

The pitch or note of a sound that we experience is The pitch or note of a sound that we experience is determined by its wavelength or its frequency. The shorter determined by its wavelength or its frequency. The shorter the wavelength, the higher the frequency becomes, and the the wavelength, the higher the frequency becomes, and the higher the pitch that we hear.higher the pitch that we hear.

The Ear picks up sound waves from the air and turns it into The Ear picks up sound waves from the air and turns it into nerve impulses that are later sent in to the brain.nerve impulses that are later sent in to the brain.

Hearing The ear is the sense organ in The ear is the sense organ in

our body that has three main our body that has three main sections, the outer, middle, sections, the outer, middle, and inner, that picks up sound and inner, that picks up sound waves. The ear is fully waves. The ear is fully developed at birth even in developed at birth even in utero, infants, respond to utero, infants, respond to sound.sound.

The outer ear consist of the The outer ear consist of the Pinna or the auricle and the Pinna or the auricle and the ear canal.ear canal.

First, the outer ear is the First, the outer ear is the sound wave collector. Its sound wave collector. Its shape helps funnel the waves shape helps funnel the waves in to the the auditory canal in to the the auditory canal (ear canal). (ear canal).

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Hearing

At the other end of the ear canal is the eardrum (tympanic At the other end of the ear canal is the eardrum (tympanic membrane). The middle ear is an air-filled cavity which membrane). The middle ear is an air-filled cavity which consists of an eardrum and three tiny, interconnected consists of an eardrum and three tiny, interconnected bones, the hammer, anvil, and stirrup. The eardrum is a bones, the hammer, anvil, and stirrup. The eardrum is a very durable and tightly stretched membrane which very durable and tightly stretched membrane which vibrates as the incoming pressure waves reach it. vibrates as the incoming pressure waves reach it. Vibrations in the eardrum are passed to the hammer, which Vibrations in the eardrum are passed to the hammer, which transmits them to the anvil, which makes the stirrup transmits them to the anvil, which makes the stirrup vibrate against the oval window of the cochlea.vibrate against the oval window of the cochlea.

Hearing Vibrations in the stirrup make waves in the fluid that travel Vibrations in the stirrup make waves in the fluid that travel

down the spiral. In the fluid, in a long strip following the down the spiral. In the fluid, in a long strip following the spiral, is the Corti. This organ is covered with (about spiral, is the Corti. This organ is covered with (about 20,000) tiny, incredibly sensitive hairs that are waving 20,000) tiny, incredibly sensitive hairs that are waving around inside the Cochlear fluid. Each of these hairs is a around inside the Cochlear fluid. Each of these hairs is a nerve ending that is picking up specific information about nerve ending that is picking up specific information about the vibrations in the fluid. At the end of the of Corti, the the vibrations in the fluid. At the end of the of Corti, the nerves are bundled together as the auditory nerve, which nerves are bundled together as the auditory nerve, which brings the information to the brain.brings the information to the brain.

Hearing and other Species Many animals hear a much wider range of Many animals hear a much wider range of

frequencies than human beings do. For example, frequencies than human beings do. For example, dog whistles vibrate at a higher frequency than the dog whistles vibrate at a higher frequency than the human ear can detect, while evidence suggests that human ear can detect, while evidence suggests that dolphins and whales communicate at frequencies dolphins and whales communicate at frequencies beyond human hearing. Frequency is measured in beyond human hearing. Frequency is measured in hertz, or the number of sound waves a vibrating hertz, or the number of sound waves a vibrating object gives off per second. The more the object object gives off per second. The more the object vibrates, the higher the frequency and the higher vibrates, the higher the frequency and the higher the pitch of the resulting soundthe pitch of the resulting sound

Species Approximate Range (Hz) human 64-23,000 human 64-23,000 dog 67-45,000 dog 67-45,000 cat 45-64,000 cat 45-64,000 cow 23-35,000cow 23-35,000 rat 200-76,000 rat 200-76,000 mouse 1,000-91,000mouse 1,000-91,000 elephant 16-12,000elephant 16-12,000 owl 200-12,000 owl 200-12,000 raccoon 100-40,000 raccoon 100-40,000 ferret 16-44,000ferret 16-44,000

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sound/u11l2d.htmlsound/u11l2d.html http://encarta.msn.com/media_461516319/http://encarta.msn.com/media_461516319/

hearing_range_in_animals.htmlhearing_range_in_animals.html http://www.lsu.edu/deafness/HearingRange.htmlhttp://www.lsu.edu/deafness/HearingRange.html