Auditory System

Question 1

List the 3 sections the ear is divided into.

Answer 1

Outer, middle and inner ear

Each part has a specific function during the hearing process.

Question 2

Where is the ear embedded?

Answer 2

The organ is embedded in the petrous portion of the temporal bone

Question 3

What is the hardest bone in the body?

Answer 3

Petrous portion of the temporal bone

Question 4

What are the 2 outer ear structures?

Answer 4

Pina and external auditory meatus

Question 5

List the outer ear functions.

Answer 5

To capture sound and to focus it to the tympanic membrane.
To amplify some frequencies by resonance in the canal.
To protect the ear from external threats (cilia prevents external elements from entering in from the air), the wax provides a mechanical function by covering the inner ear and provides an unfavourable pH to pathogens.

Question 6

What is the main function of the middle ear?

Answer 6

Amplification by:

• Focusing vibrations from large surface area (tympanic membrane) to small surface area (oval window). The change in surface area means the pressure is increased.
• Using leverage from the incus-stapes joint to increase the force on the oval window.

Question 7

What 3 structures articulate with each other to facilitate the transmission of sound into the inner ear?

Answer 7

Malleus, incus and stapes

Question 8

What is the hearing part of the inner ear?

Answer 8

Cochlea

Question 9

Describe the relationship between surface area and pressure.

Answer 9

Inversely proportional

Question 10

What is the function of the inner ear?

Answer 10

To transduce vibration into nervous impulses. While doing so, it also produces a frequency (or pitch) and intensity (or loudness) analysis of the sound.

Question 11

The cochlea contains 3 compartments. Name them.

Answer 11

Scala vestibuli
Scala media
Scala tympani

Question 12

What 2 compartments of the cochlea are bone structures containing perilymph (high in sodium)?

Answer 12

Scala vestibuli and scala tympani

Question 13

What is the Scala media?

Answer 13

Membranous structure containing potassium-rich endolymph. The hearing organ, the Organ of Corti resides within the scala media of the cochlea.

Question 14

Is the perilymph high in sodium or potassium?

Answer 14

Perilymph HIGH IN SODIUM whereas endolymph is high in potassium.

Question 15

Where is the hearing organ or Organ of Corti located?

Answer 15

Scala media of cochlea

Question 16

What is the name of the structure that the organ of Corti lies in?

Answer 16

Basil membrane

Question 17

Describe how the basilar membrane is arranged.

Answer 17

Arranged tonotopically using the same principle as a xylophone whereby frequency-sensitive cells are arranged from high to low frequency from base to apex respectively.

Question 18

Explain the arrangement of hair cells in the Organ of Corti.

Answer 18

Contains inner and outer hair cells. Inner hair cells are arranged in single columns whereas outer hair cells are arranged in columns of three.

Question 19

Where is the tectorial membrane located relative to the hair cells and what is its purpose?

Answer 19

The tectorial membrane is located above the hair cells and will allow the hair deflection, which in turn will depolarise the cell.

Question 20

Are OHC and IHC in contact with the tectorial membrane?

Answer 20

No, only OHC hair are in constant contact with the tectorial membrane and these assist the contact with the IHC.

Question 21

What is the function of IHC in the Organ of Corti?

Answer 21

IHC carry 95% of the afferent information of the auditory nerve. Their function is the transduction of the sound into nerve impulses.

Question 22

What is the function of OHC in the Organ of Corti?

Answer 22

Carry 95% of efferents of the auditory nerve. Their function is modulation of the sensitivity of the response.

Question 23

Explain the process of transduction.

Answer 23

Deflection of the stereocilia towards the longest cilium will open K+ channels within the inner hair cell, as the tectorial membrane is brought into contact. Ionic interchange of potassium within the endolymph and inner hair cell leads to cell depolarisation. Depolarisation induces the opening of VGCCs which release excitatory NTs (Glutamate) onto the afferent nerve.

Question 24

What is the relationship between amplitude of sound and deflection of sterocilia causing K+ channel opening?

Answer 24

Higher amplitudes of sound will cause greater deflection of stereocilia and K+ channel opening.

Question 25

What are the hair of the hair cells called?

Answer 25

Stereocilia

Question 26

In transduction what will open K+ channels and what will close K+ channels?

Answer 26

Depolarisation - opens K+ channels Hyper-polarisation - closes K+ channels

Question 27

Explain the auditory pathways in the human body.

Answer 27

Spiral ganglions from each cochlea project via the auditory vestibular nerve (VIII) to the ipsilateral cochlear nuclei (monoaural neurons). Auditory information crosses the superior olive level, beyond this point all connections are bilateral. Ultimately information is relayed to the auditory cortices located within the temporal lobe.

Question 28

Use one word to describe how hearing is organised.

Answer 28

Tonotopically

Question 29

Define frequency

Answer 29

Frequency/pitch (Hz) - Cycles per second, perceived tone

Question 30

Define amplitude.

Answer 30

Amplitude/loudness (dB) - Sound pressure, subjective attribute correlated with physical strength.

Question 31

Define the human range of hearing for both frequency and amplitude.

Answer 31

Frequency: 20-20,000 Hz Loudness: 0dB-120dB sound pressure level (SPL)

Question 32

What type of scale is the decibel scale?

Answer 32

Logarithmic scale

Question 33

Why is the decibel scale useful?

Answer 33

Because the range of sensitivity is very large. This allows us to compress the scale on a graph, and reflect the fact that many physiological processes are non-linear (i.e. they can respond to both very low and very high values).

Question 33

Why is the decibel scale useful?

Answer 33

Because the range of sensitivity is very large. This allows us to compress the scale on a graph, and reflect the fact that many physiological processes are non-linear (i.e. they can respond to both very low and very high values).

Question 34

Does hearing acuity decrease with age?

Answer 34

Yes, particularly with higher frequencies. Medium and low frequencies could be affected with the progression of a hearing loss.

Question 35

What are the aims of the hearing assessment?

Answer 35

To answer these questions: Is there a hearing loss? If yes: - Of what degree? - Of what type?

Question 36

List the procedures involved in a hearing assessment.

Answer 36

``` Tunning fork Audiometry Central processing assessment Tympanometry Otoacustic Emission Electrocochleography ```

Question 37

What is the use of a tuning fork in the hearing assessment?

Answer 37

Used to establish the probable presence or absence of a hearing loss with a significant conductive component. They are used to provide early and general information, when audiometry is not available or possible.

Question 38

What is Pure Tone Audiometry?

Answer 38

Science of measuring hearing acuity for variations in sound intensity and frequency. An audiometer is the device used to produce sound of varying intensity and frequency.

Question 39

Describe how you would complete the Weber test.

Answer 39

Place tuning fork against knee or elbow and then place the base of the form in the midline on the patient’s forehead. Ask the patient whether the sound is louder in any particular ear. Unilateral conductive hearing loss - sound will be heard louder in the deaf ear. Unilateral sensorineural hearing loss - sound will be heard louder in the normal ear.

Question 40

Describe how you would complete the Rinne test.

Answer 40

Compares air conduction with bone conduction. Place base of vibrating tuning fork against the patient’s mastoid process (Allow for 2-3 seconds to appreciate intensity of sound). Lift the fork off the mastoid process and place the vibrating tips about 1cm from their external auditory meatus.

Question 41

Explain what an audiogram is.

Answer 41

The audiogram is where the hearing thresholds are plotted to define if there is a hearing loss or not. A normal hearing threshold is located between 0-20dB.

Question 42

What is the Central Processing Assessment?

Answer 42

Assessment of hearing abilities other than detection. This involves sound localisation, filtered speech and speech in nose. Focused on assessing sound discrimination and comprehension.

Question 43

What is the Tympanometry examination used to test?

Answer 43

Condition of the middle ear and mobility of the ear drum (tympanic membrane) and the ossicles by generating variations of air pressure in the ear canal.

Question 44

List the most common results of tympanometry.

Answer 44

A - Normal C - Negative middle ear pressure B - Middle ear effusion, perforation of tympanic membrane, Eustacian (pharyngotympanic) tube dysfunction, occluded ear canal.

Question 45

What is compliance of the the middle ear?

Answer 45

How effectively sound is transmitted into the middle ear.

Question 46

The normal cochlea produces low intensity sounds called what?

Answer 46

Otoacoustic Emissions (OAEs)

Question 47

What are OAEs produced specifically by?

Answer 47

Outer hair cells as they expand and contract.

Question 48

What test is often part of the newborn hearing screening and hearing loss monitoring?

Answer 48

Otoacoustic Emissions (OAEs)