4. The cochlea is the place where sound energy is converted into neural impulses—a process called transduction.
The neural impulses flow out of the cochlea, through the auditory nerve on the way toward the brain.
Chapter 29. The Auditory Pathway
Learning Objectives
auditory canal
tube in the outer ear that channels sound waves to the eardrum
auditory cortex
region in the temporal lobe of the brain’s cerebral hemispheres that is the primary area for hearing and processing speech sounds
auditory nerve
carries neural impulses from the inner ear toward the brain
basilar membrane
thin membrane that separates the cochlea into two main chambers; contains the auditory receptors (hair cells)
cochlea
coiled, fluid-filled tube in the inner ear in which sound vibrations trigger nerve impulses
eardrum
thin membrane that vibrates in response to incoming sound waves; separates auditory canal from middle ear
hair cells
receptor cells for the auditory system; located within the cochlea on the basilar membrane
hemisphere
one half of the brain; divided into four lobes
inner ear
innermost part of the ear, containing the cochlea and semicircular canals
middle ear bones
the three small bones within the middle ear that amplify the eardrum vibrations and pass them on to the cochlea
neural impulse
an electrical signal that carries a message along an axon
neurotransmitters
chemical messengers released by the axon terminal into the synaptic gap between neurons
outer ear
external portion of the ear, including pinna, auditory canal, and eardrum
pinna
part of the outer ear that protrudes from the head
temporal lobes
part of the cerebral cortex, located in the lower portion of the brain on each side of the head; processes information from the ears
thalamus
main relay center in the brain for sensory information on the way to processing areas in the cortex
transduction
converting energy from external stimuli into neural impulses that the brain can understand
The Auditory Pathway
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Learning Objectives:
Name the major structures of the auditory system.
Understand the role of each auditory system structure in transmitting auditory information.
Review
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Review
Select the NEXT button to continue with the Review.
Capturing the Sound Wave
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1. How does the ear transform sound waves into nerve impulses that our brain can understand?
When a sound wave reaches our head, the pinna (external portion of the outer ear) funnels the sound through the auditory canal to the eardrum.
Review
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Review
Play the animation to watch sound waves being amplified. Then select the NEXT button to continue with the Review.
Amplifying the Sound Wave
2. The alternating bands, or regions, of high and low pressure in the sound wave cause the eardrum to vibrate at the same rate as the object that produced the sound wave.
Vibrations of the eardrum pass through the three small middle ear bones, which serve as a sort of primitive amplifier to intensify the vibrations. When the vibrations reach the cochlea (a snail-shaped tube in the inner ear), they jostle the fluid that fills the tube.
Review
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Review
Play the animation to watch auditory receptors being stimulated. Then select the NEXT button to continue with the Review.
Stimulating the Auditory Receptors
3. The movement of the fluid within the cochlea bends the tiny hair cells on the basilar membrane. This causes the hair cells to release neurotransmitters.
The greater the intensity of the sound, the more the hair cells are bent, and then more neurotransmitters are released.
Review
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Select the PLAY button to watch the sound wave being converted to neural impulses. Then select the NEXT button to continue with the Review.
Converting the Sound Wave to Neural Impulses
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Review
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Review
Play the animation to watch neural impulses travel from the left ear to the auditory cortex in each brain hemisphere. Then select the NEXT button to continue with the Review.
Carrying the Sound Code to the Brain
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5. The neural impulses from the cochlea pass through the auditory nerve to the thalamus—the relay station for the senses—in the center of the brain.
From there they are relayed on to the auditory cortex (in the temporal lobe of each brain hemisphere) for further processing and interpretation.
Most of the signals from the left ear cross over to the auditory area in the right hemisphere, but a small portion of the signals goes directly to the auditory area of the left hemisphere. The reverse is true for the right ear.
As a result, most of the information contained in the sound wave ends its journey in the hemisphere opposite the ear that detected the sound.
Quiz 1
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Quiz 1
Drag each description to the appropriate gray area to form the correct sequence of events that occurs when sounds are processed by the auditory system. When all the descriptions have been placed, select the CHECK ANSWER button.
Quiz 2
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Quiz 2
For each statement, select one of the buttons to indicate whether the statement is True or False. When responses have been placed for all of the statements, select the CHECK ANSWER button.
Conclusion
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