Exam #6: Auditory System

Question 1

What is sound i.e. what is the physical stimulus for audition?

Answer 1

Periodic condensation and rarefaction of air molecules

*****Note you need a higher frequency tuning fork compared to vibratory sense

Question 2

What is a dB?

Answer 2

0.0002 dyne/cm2

Question 3

What is the frequency range of human hearing? What is the normal human hearing range? How does the normal hearing range change with age?

Answer 3

Absolute Range= 20 Hz - 20 kHz (cycles per second)
Normal= 20Hz to 16kHz

**There is a decline in ability to hear higher frequencies with age, called presbycusis

Question 4

What is the pressure range of human hearing?

Answer 4

0 dB- ~130 dB

Question 5

What is a notch in an audiogram? What causes this notch?

Answer 5

Frequency at which the a sound need to be much more powerful to be heard compared to adjacent frequencies in that range

**Caused by a v. loud sound that kills hair cells e.g. explosion, gunshot….etc.

Question 6

Describe the transduction of sound from outer ear to inner ear.

Answer 6

• External ear directs sound waves into the auditory canal
• Auditory canal transmits sound waves to the TM
• Sound waves move TM, which moves the chain of ossicles
• Footplate of the stapes is pushed into the oval window, which displaces fluid in the inner ear

Question 7

What part of the auditory system facilitates the equalization of pressure?

Answer 7

Eustachian tube

Question 8

What nerves innervate the inner ear muscles?

Answer 8

CN V & VII

Question 9

What is the function of contracting the inner ear muscles?

Answer 9

Protection from loud sound i.e. attenuation reflex

Question 10

What is the afferent limb of the middle ear attenuation reflex?

Answer 10

CN VIII

Question 11

What is the efferent limb of the middle attenuation reflex?

Answer 11

CN VII to stapedius m.

CN V to tensor tympani

Question 12

Lesion of what nerve/ accompanying muscle are responsible for the hyperacusis seen in Bell’s Palsy?

Answer 12

CN VII & stapedius m.

Question 13

What is the Organ of Corti? What are the different parts of the Organ of Corti? What membranes separate these three different regions

Answer 13

The Organ of Corti is the sensory transduction apparatus for audition in the cochlea of the inner ear. It contains: 
Scala vestibuli 
--Reissner's membrane 
Scala media 
--Basilar membrane 
Scala Tympani

Question 14

What fluid-type is in each region of the inner ear?

Answer 14

Scala vestibuli= Perilymph
Scala media= Endolymph
Scala Tympani= Perilymph

Question 15

What produces endolymph?

Answer 15

Stria vascularis

Question 16

Where is the base of the auditory hair cells (stereocilia)? What membrane are the tips of the auditory hair cells embedded in?

Answer 16

Base= Basilar membrane of the Scala Media 
Tip= Tectorial membrane of the Scala Media

Question 17

Outline the steps of auditory transduction.

Answer 17

1) Sound waves
2) Vibration of organ of Corti
3) Bending of cilia in Scala Media
4) Change in K+ conductance to cause depolarization & hyperpolarization
5) Oscillating receptor potential i.e. cochlear microphonic
6) Glutamate release
7) Action potential

Question 18

What is the difference between inner & outer hair cells

?

Answer 18

Inner= actual sensory receptors

• Fewer
• Single row

Outer=

• More
• Parallel rows

Question 19

What frequency of sound is heard at the base of the cochlea?

Answer 19

High 1,600 Hz

Question 20

What frequency of sound is heart at the apex of the cochlea near the helicotrema?

Answer 20

Low 25 Hz

Question 21

Outline the pathway of auditory input.

Answer 21

1) Cochlea
2) CN VIII
3) Dorsal & ventral cochlear nuclei (medulla)
4) Lateral lemniscus
5) Inferior colliculus
6) Medial geniculate nucleus of thalamus
7) Auditory cortex

Question 22

What is efferent control?

Answer 22

Olivocochlear bundle in the superior olivary complex sharpens frequency

Question 23

How do we know if the sound comes from the right or left?

Answer 23

LSO neurons encode sound location based off sound intensity

**Lateral superior olive

Question 24

For low frequency sounds, how do you determine location?

Answer 24

Time of arrival

Question 25

What are the different types of deafness?

Answer 25

Conductive
Sensorineural
Central

Question 26

What is conductive deafness?

Answer 26

Deafness caused by impaired transmission in the external or middle ear

Question 27

What is sensorineural hearing loss?

Answer 27

Deafness caused by the loss of hair cells

Question 28

What are the typical causes of conductive deafness?

Answer 28

Cerumen impaction 
Otosclerosis 
Fibrosis from OM 
OM w/ effusion 
Damage to DM

Question 29

What are the typical causes of sensorineural deafness?

Answer 29

Ototoxic drugs
Excessive noise
Vestibular Schwannoma
Meniere’s Syndrome

Question 30

What is is BAER?

Answer 30

Brainstem evoked response

Question 31

What is a response or tone-click hearing test?

Answer 31

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Question 32

What is audiometry?

Answer 32

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Question 33

Where is the primary auditory cortex?

Answer 33

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