Module 20 REVIEW

• 20-1 What are the characteristics of air pressure waves that we hear as sound?

• Sound waves are bands of compressed and expanded air. Our ears detect these changes in air pressure and transform them into neural impulses, which the brain decodes as sound.
• Sound waves vary in amplitude, which we perceive as differing loudness (measured in decibels), and in frequency, which we experience as differing pitch.

• 20-2 How does the ear transform sound energy into neural messages?

• The outer ear (the visible portion of the ear and the auditory canal) funnels sound to the middle ear (the chamber between the eardrum and cochlea).
• The inner ear consists of the cochlea, semicircular canals, and vestibular sacs.
• Sound waves traveling through the auditory canal cause tiny vibrations in the eardrum. The bones of the middle ear (the hammer, anvil, and stirrup) amplify the vibrations and relay them to the fluid-filled cochlea. Rippling of the basilar membrane, caused by pressure changes in the cochlear fluid, causes movement of the tiny hair cells, triggering neural messages to be sent (via the thalamus) to the auditory cortex in the brain.
• Sensorineural hearing loss (or nerve deafness) results from damage to the cochlea’s hair cells or their associated nerves. Conduction hearing loss results from damage to the mechanical system that transmits sound waves to the cochlea. Cochlear implants can restore hearing for some people.

• 20-3 How do we detect loudness, discriminate pitch, and locate sounds?

• Our brain interprets loudness from the number of activated hair cells (and louder sounds activate greater numbers of hair cells).
• Place theory explains how we hear high-pitched sounds, and frequency theory explains how we hear low-pitched sounds. A combination of the two theories explains how we hear pitches in the middle range.
• Place theory proposes that our brain interprets a particular pitch by decoding the place where a sound wave stimulates the cochlea’s basilar membrane.
• Frequency theory proposes that the brain deciphers the frequency of the neural impulses traveling up the auditory nerve to the brain. By alternating their firing (the volley principle), neural cells enable us to sense sounds with frequencies that exceed the firing speed of an individual neuron.
• Sound waves strike one ear sooner and more intensely than the other. The brain analyzes the minute differences in the sounds received by the two ears and computes the sound’s source.

Multiple-Choice Questions

1. Your friend is playing the low notes on her tuba quite loudly. Which of the following best explains the physical properties of the sound waves?
   1. No wavelength; large amplitude
   2. Short wavelength; large amplitude
   3. Short wavelength; small amplitude
   4. Long wavelength; large amplitude
   5. No wavelength; small amplitude
2. After being exposed to loud music for many years, which of the following types of deafness is more likely in a musician?
   1. Conduction
   2. Accommodation
   3. Sensorineural
   4. Basilar
   5. Frequency
3. Which of the following reflects the notion that pitch is related to the stimulation of different areas of the cochlea’s basilar membrane?
   1. Place theory
   2. Frequency theory
   3. Volley principle
   4. Sound localization
   5. Stereophonic hearing
4. When you listen to music, the sound waves cause your _____ to vibrate first.
   1. cochlea
   2. hammer, anvil, and stirrup
   3. eardrum
   4. oval window
   5. auditory nerve

Practice FRQs

1. Identify the role of the eardrum, three bones in the middle ear, and oval window in transmitting sound waves before they reach the hair cells.

Answer

1 point: The eardrum will vibrate in response to the sound waves. Page 199

1 point: The three bones (hammer, anvil, and stirrup) in the middle ear transmit sound waves between the eardrum and the oval window. Page 199

1 point: The oval window is the point at which vibrations enter the cochlea. Page 199

2. How are the following activated as you listen to the soundtrack of your favorite film?
   • Cochlea
   • Auditory nerve
   • Auditory cortex

(3 points)