CHAPTER 2: SOUND Section 4: How you Hear Sound

Discover Activity: Where is Sound Coming From? 1. Ask your partner to sit on a chair, with eyes closed 2. Clap your hands near your partner’s left ear. Ask your partner what direction the sound came from. Record the answer. 3. Now clap your hands near your partner’s right ear. Again, ask your partner what direction the sound came from and record the answer. Continue clapping in different locations around your partner’s head and face. How well did your partner identify the directions the sounds came from? 4. Switch places with your partner and repeat step 1-3. Observing: From which locations are claps easily identified? For which locations are claps impossible to identify? Is there a pattern? If so, suggest an explanation for the pattern.

I. The Human Ear: A. Three sections to the Ear: 1. outer ear = funnels sound waves 2. middle ear = transmits the waves inward 3. inner ear = converts sound waves into a form that travels to your brain. a form that travels to your brain. B. Outer Ear: 1. looks and acts like a funnel 2. collects sound waves 3. ear canal: a narrow region that is a few cm’s long and ends at the eardrum ends at the eardrum

4. eardrum- a small tightly stretched, drumlike membrane. a. Sound waves cause the eardrum to vibrate C. Middle Ear: 1. located behind the eardrum 2. contains the three smallest bones in the body a. Hammer-attached to the eardrum (also vibrates) b. Anvil-receives vibration from the hammer c. Stirrup-receives vibration from the anvil the anvil

D. Inner Ear: 1. Separated from the middle ear by a membrane 2. Contains the cochlea- a fluid-filled cavity shaped like a snail shell. a. Contains more than 10,000 hair cells b. Hair cells carry the sound waves as messages to the auditory nerve which carries the signal to the brain.

II. Hearing Loss: A. When a person has a hard time hearing soft sounds or high-pitched hearing soft sounds or high-pitched sounds sounds B. Causes of Hearing loss: 1. injury- eardrum is damaged or punctured. or punctured. - try not to put things in your ears ears 2. infection – damages the delicate inner ear inner ear

C. Causes of Hearing Loss cont’d: 3. exposure to loud sounds- causes damage to hair cells in the ear the ear - damaged cells do not - damaged cells do not transmit signals to the brain transmit signals to the brain 4. aging- occurs gradually a. Hair cells in the cochlea die and are not replaced b. Results in not being able to hear high sounds c. Wear ear protection to avoid hearing loss

D. Hearing Aids- D. Hearing Aids- 1. can restore some lost hearing 1. can restore some lost hearing 2. amplify sounds coming into the ear 3. can amplify specific frequencies as well