Anatomy and Physiology of Hearing

Question 1

Peripheral auditory system

Answer 1

• external ear
• middle ear
• inner ear

Question 2

Central auditory system

Answer 2

• cranial nerve VII
• brain stem
• brain

Question 3

Outer Ear function

Answer 3

• locates sound in the environment
• collects the sound
• funnels the sound to they tympanic membrane via the external auditory meatus

Question 4

Middle Ear function

Answer 4

• acoustic energy hits the tympanic membrane
• Tympanic membrane starts to vibrate indicating an energy change: acoustic energy has been changed into mechanical energy
• the mechanical energy is transmitted through the ossicles (malleus, incus, stapes)
• footplate of stapes rocks in and out of the oval window

Question 5

Inner Ear function

Answer 5

• Rocking of the stapes creates waves in the cochlear fluid
• 2nd energy change: mechanical energy has been changed into hydraulic energy
• the waves disrupt hair cells in the organ of Corti causing a third energy change: hydraulic energy changed to electrochemical energy

Question 6

Nerve Transmission

Answer 6

• Cranial nerve VIII is the vestibulocochlear nerve
• the cochlear branch of this nerve connects to the hair cells of the organ of corti
• nerve conducts or transmits the electrochemical impulse generated at the hair cells to the brainstem

Question 7

Brain Processing

Answer 7

• Primary Auditory Cortex (PAC): this area is tonographically (or tonotopically) organized, like the cochlea and the rest of the central auditory system (there are different parts of this area that are sensitive to different frequencies of sound); functionally perceives and discriminates sound
• Wernicke’s Area (PAC): also on the superior temporal gyrus; important for attaching meaning to heard speech; damage to WA can cause Warnicke’s aphasia where patients have severe auditory comprehension deficits