80 - Special Senses I (Auditory)

Question 1

Be able to state the normal human hearing range

Answer 1

20-20,000 Hz

People 25 years or older typically can’t hear above 16,000 Hz (16 kHz)

Question 2

Be able to give the range of frequencies to which humans are most sensitive

Answer 2

Most sensitive range = 1-4 kHz

Question 3

Describe presbycuspis

Answer 3

• Presbycusis or Age Related Hearing Impairment (ARHI)- is hearing loss in older people, first apparent in high frequency hearing range.
• Several possible genetic causes.
• Recently discovered that certain gene variants for a metabotropic glutamate receptor are associated with an increased chance of developing ARHI.

Question 4

What is “loudness”?

Answer 4

a. Loudness is a psychophysical measurement of the perception of intensity of sound
b. Depends on both frequency and sound pressure

Question 5

How do we measure the sound pressure level? (one aspect of loudness)

Answer 5

Sound Pressure Level (SPL) in dB:
SPL = 20 log (sound pressure/reference pressure)
SPL = 20 log (P/Pr)

Question 6

What does the dB value mean?

Answer 6

0 dB means pressure of sound equals reference pressure

If sound pressure if weaker than reference pressure, sound will have negative dB value

Question 7

What is the function of the outer ear?

Answer 7

AKA the pinna - In humans the pinnae are important in localizing sound in the vertical plane

Question 8

How does the outer ear accomplish this?

Answer 8

• The external auditory meatus has resonant frequency of about 3,500 Hz.
• This increases the sound pressure at the tympanic membrane for certain frequencies (especially around 2.5 to 4 kHz)

Question 9

What are the functional components of the middle ear?

Answer 9

• Auditory tube or Eustachian tube

- Ossicular system

Question 10

What is the function of the Eustachian tube?

Answer 10

Air pressure in the middle ear can be equalized with that in the external environment

Question 11

What is the ossicular system of the middle ear? What is its function?

Answer 11

The malleus, incus and stapes

Function: provides impedance match between outer and inner ear: air in outer ear has low impedance (resistance to movement) and fluid in inner ear has high impedance. To enable transmission of sound from air to the inner ear, the middle ear increases the pressure felt at the tympanic membrane to a higher pressure at the oval window.

Question 12

Describe the process by which sound energy is transformed into neural signals (something the brain can process)

Answer 12

1 - Sound enters external auditory canal
2 - Pressure of sound waves moves tympanic membrane
3 - Ossicles transmit pressure from sound waves into cochlea
4 - Cochlea contains organ of Corti, which contains auditory hair cells
5 - Pressure from sound waves moves endolymph, which in turn moves hairs cells & depolarizes them
6 - Depolarization results in action potential sent to brain via auditory nerve & sound is “heard”

Question 13

What two muscles are found in the middle ear?

Answer 13

1 - Stapedius muscle

2 - Tensor tympani

Question 14

Which nerve innervates the stapedius?

Answer 14

CN VII (facial nerve)

Question 15

Which nerve innervates the tensor tympani?

Answer 15

CN V (trigeminal)

Question 16

What is the middle ear attenuation reflex?

Answer 16

A reflex that involves both muscles of the middle ear contracting in response to loud noise, but the stapedius is responsible for most of the attenuation of the noise (opposite of amplification)

Question 17

Given that the stapedius and tensor tympani are both involved in the middle ear attenuation reflex, which nerves are involved?

Answer 17

Stapedius - CN VII (facial)

Tensor tympani - CN V (trigeminal)

Question 18

What is the function of the middle ear attenuation reflex?

Answer 18

Attenuation of sound most pronounced for frequencies below 1 kHz. Since low frequency sound interferes with perception of higher frequency sounds, the attenuation reflex is believed to aid in understanding speech in a noisy environment.

Question 19

What is hyperacusis?

Answer 19

A health condition characterized by an over-sensitivity to certain frequency and volume ranges of sound (a collapsed tolerance to usual environmental sound).

Question 20

What is the place theory of hearing?

Answer 20

Place theory is a theory of hearing which states that our perception of sound (high or low frequency) depends on where each component frequency produces vibrations along the basilar membrane of the cochlea

Question 21

Which area of the basilar membrane of the cochlea recognizes high/low frequency?

Answer 21

• Higher frequencies recognized near base

- Lower frequencies recognized near apex

Question 22

What is the concept of the traveling wave on the basilar membrane?

Answer 22

This aspect of the Place Theory of hearing describes basilar membrane movement

Travelling waves always start at the narrow, stiffer part of basilar membrane and travel toward the wider, floppy part

Question 23

Which part of the basilar membrane of the cochlea is stiff and narrow?

Answer 23

The area near the stapes or base of cochlea (where higher frequencies are recognized)

Question 24

Which part of the basilar membrane is wide and floppy?

Answer 24

The helicotrema or apex of the cochlea (where lower frequencies are recognized)

Question 25

What are the three types of deafness?

Answer 25

1 - Conductive deafness
2 - Sensorineural deafness
3 - Central hearing loss

Question 26

What causes conductive deafness?

Answer 26

It is due to impaired sound transmission in the external or middle ear

Question 27

What are some examples of things that cause conductive deafness?

Answer 27

examples:
- plugging of the external ear canal with wax or foreign bodies
- otosclerosis (stapedial otosclerosis)
- fibrosis due to repeated middle ear infections
- otitis media with effusion - fluid accumulation in the middle ear
- damage to the tympanic membrane

Question 28

What is sensorineural deafness?

Answer 28

Usually due to loss of cochlear hair cells

Question 29

What things can cause sensorineural deafness?

Answer 29

• Hair cell damage by ototoxic drugs (amnioglycoside antibiotics)
• Noise exposure (temporary and permanent)
• Vestibular schwannoma (benign intracranial tumor of the myelin-forming cells of the vestibulocochlear nerve - unilateral)

Question 30

What are the treatment options for sensorineural deafness?

Answer 30

• If auditory nerve intact and sufficient hair cells remaining, patient can be treated successfully with hearing aids.
• When most or all of hair cells lost only possible treatment is use of a cochlear prosthesis

Question 31

What is central hearing loss?

Answer 31

• Hearing impairments caused by lesions to central auditory nuclei and pathways.
• These lesions sometimes called retrocochlear lesions.

Question 32

Will central hearing loss be unilateral or bilateral? What condition can cause this?

Answer 32

• There is so much midline crossing of auditory information that unilateral damage to ascending auditory pathways has only subtle effects on hearing.
• Multiple sclerosis, which affects central myelin, can cause defective sound localization.

Question 33

What is the brainstem auditory evoked response (BAER)?

Answer 33

Brainstem auditory evoked response (BAER) is a test to measure the brain wave activity that occurs in response to clicks or certain tones.

Question 34

How do you perform the BAER test?

Answer 34

You lie on a reclining chair or bed and remain still. Electrodes are placed on your scalp and on each earlobe. The earphones give off a brief click or tone. The electrodes pick up the brain’s responses to these sounds and record them. You do not need to be awake for this test.

Question 35

Why would you perform the BAER test?

Answer 35

• Help diagnose nervous system problems and hearing loss (especially in newborns and children)
• Determine how well the nervous system works
• Determine hearing ability in people who can not do other hearing tests.

Question 36

What is an evoked otoacoustic emission?

Answer 36

a sound which is generated from within the inner ear

Question 37

How is this clinically relevant?

Answer 37

Studies have shown that OAEs disappear after the inner ear has been damaged, so OAEs are often used in the laboratory and the clinic as a measure of inner ear health.

Question 38

When would you test OAEs to determine hearing ability?

Answer 38

Otoacoustic emissions are clinically important because they are the basis of a simple, non-invasive test for hearing defects in newborn babies and in children who are too young to cooperate in conventional hearing tests.

Question 39

What is audiometry?

Answer 39

• Typically, audiometric tests determine a subject’s hearing levels with the help of an audiometer, but may also measure ability to discriminate between different sound intensities, recognize pitch, or distinguish speech from background noise.
• Acoustic reflex and otoacoustic emissions may also be measured.
• Results of audiometric tests are used to diagnose hearing loss or diseases of the ear, and often make use of an audiogram.

Question 40

What is the location of the primary auditory cortex?

Answer 40

Brodmann’s areas 41 & 42 in the temporal lobe