Anatomy / Physiology of the Ear, and Physiology and Clinical Aspects of Hearing and Balance

Question 1

Which bones form part of the middle ear?

Answer 1

• The ossicles*
• Malleus (hammer)
• Incus (anvil)
• Stapes (stirrup)

Question 2

Which bones form part of the inner ear?

Answer 2

• Semicircular canals

- Cochlea

Question 3

What is the function of the middle ear ossicles?

Answer 3

• Transmits the vibratory motion of the eardrum (tympanic membrane) to the oval window
• Transforms acoustic energy from the medium of air to the medium of fluid -> acts as a sound amplifier!!

Question 4

What structures do sound-waves encounter (in order) when travelling through the middle ear?

Answer 4

• Outer ear*
• Auricle (pinna)
• External auditory canal
• Tympanic membrane (eardrum)
• Middle ear*
• Malleus
• Incus
• Stapes
• Oval window
• Inner ear*
• Cochlea (hair cells in organ of Corti, w tectorial membrane above and basilar membrane below): oval window -> up scala vestibuli -> to the helicotrema -> down scala tympani -> round window

Question 5

What is the pathophysiology of Otitis Media w Effusion? (AKA “Glue Ear”)

Answer 5

• Middle ear filled with fluid instead of air
• Affects movement of the Tympanic membrane
• Causes conductive hearing loss (bc sound-waves cannot be transmitted through the middle ear!)

Question 6

What is the pathophysiology of Otosclerosis?

Answer 6

• Deposition of new bone where footplate of Stapes fits into oval window
• Reduces movement of Stapes’ footplate causing a conductive hearing loss
  (bc the lever action of the ossicles is now messed up!)

Question 7

What structures make up the Organ of Corti?

Answer 7

• Tectorial membrane above
• Cilia on top of (inner and outer) Hair cells
• Basilar membrane below

Question 8

Describe the hearing mechanism in the Cochlea

Answer 8

• Footplate of stapes moves in and out of oval window, creating a travelling wave in the scala vestibuli (up) and scala tympani (down) of the cochlea
• This causes a movement of the Basilar membrane and movement of the inner and outer hair cells in the Organ of Corti in relation to the tectorial membrane
• The cilia of the hair cells are deflected and ion channels open
• Cations flow from the endolymph into the hair cells
• Depolarisation takes place and an impulse is sent up the cochlear nerve
• Inner hair cells activate afferent nerves
• Outer hair cells modify the response of the inner hair cells

Question 9

Describe the phrase “Tonotopic Arrangement”

Answer 9

• For every frequency, there is a specific place on the Basilar membrane where the hair cells are maximally sensitive to that frequency
  (ie. hair cells closer to the oval window are more sensitive to higher frequencies, whereas hair cells further from the oval window are more sensitive to lower frequencies)
• This tonotopic arrangement continues through the auditory pathway up to the acoustic area of the Temporal lobe (where certain areas are more sensitive to certain frequencies)

Question 10

How can you assess hearing in the clinic?

Answer 10

• Clinical Testing
  (ie. covering pt’s eyes or going behind them while saying words)
• Tuning fork tests
• Audiometry
• Objective testing (ie. Tympanometry, OAEs)

Question 11

What are the different types of Tuning fork tests?

What is the purpose of them?

Answer 11

• Weber’s, Rinne’s

- To differentiate whether the hearing loss is conductive or sensorineural

Question 12

What is the purpose of a Weber’s test?

Answer 12

• A test of lateralisation

- Tells u in what ear there is hearing loss

Question 13

How do you interpret the results of a Weber’s test?

Answer 13

• With no hearing loss: sound is NOT heard best in any ear
• With conductive hearing loss: sound is heard best in the AFFECTED ear
• With sensorineural hearing loss: sound is heard best in the UNAFFECTED ear

Question 14

What is the purpose of a Rinne’s test?

Answer 14

• Compares loudness of perceived air conduction to bone conduction, in one ear at a time
• Tells u whether the hearing loss is conductive or not

Question 15

How do you interpret the results of a Rinne’s test?

Answer 15

• Air louder than bone (Rinne’s +ve) = normal or sensorineural hearing loss (false-positive)
• Bone louder than air (Rinne’s -ve) = conductive

Question 16

Who is pure tone Audiometry used for?

Answer 16

• First-line diagnostic test for pt’s hearing loss

- Older children + Adults

Question 17

Who is visual reinforcement Audiometry used for?

Answer 17

• First-line diagnostic test for pt’s hearing loss

- Babies!

Question 18

Who is play Audiometry used for?

Answer 18

• First-line diagnostic test for pt’s hearing loss

- children aged 2-5 years, learning disabilities

Question 19

What are the different objective hearing tests?

Answer 19

• Tympanometry
• > tests the movement of the eardrum
• > ie. whether it is stiff, there is a hole in it, or it moves too much
• OAEs (Otoacoustic Emissions)
• > sound stimulating the cochlea produces soft sounds which echoes back into the middle ear -> detected by a probe
• > children w significant hearing loss do not produce those echoes
• > part of Newborn Screening Programme in Scotland

Question 20

How is volume and pitch of sound identified in relation to the sound waves?

Answer 20

• Volume = amplitude of waves (ie. how long the wave is )

- Pitch = frequency of waves (ie. how many waves there are in a given space of time)

Question 21

What does a large “air-bone gap” indicate?

Answer 21

Significant conductive hearing loss

Question 22

What is the management of hearing loss?

Answer 22

• Surgery (ie. grommets)
• > (ie. mostly for conductive)
• Sound amplification
• > (ie. mostly for sensorineural)
• Direct stimulus of cochlear nerve cells (ie. w a super hearing aid)
• > (if v severe sensorineural hearing loss)

Question 23

Who is an open-fit hearing aid used for?

Answer 23

• Osseous integrated screw into skull -> sound conducts through skull into cochlea*
• ie. BAHA -> Bone Anchored Hearing Aid*
• Used by those whose anatomy makes use of conventional aid difficult, ie. persistent otitis externa, external canal stenosis

Question 24

Which part of the ear controls balance?

Answer 24

The vestibular labyrinth! (inner ear)

Question 25

Describe the components of the vestibular labyrinth

Answer 25

2 Otolith organs -> contain otoconia which gives them their name of “otolith” organs!

• Utricle: 3 semi-circular canals
• Saccule

Question 26

What is the function of the Ampullae of the Semi-circular canals?

Answer 26

• The ampullae are the expanded areas at each end of the semi-circular canals
• They contain the sensory organ: crista ampullaris (cupula, hair cells) -> detects angular (rotational) acceleration
• Movement of the crista is the stimulus for the vestibulo-ocular reflex

Question 27

What is the role of the macula in the Otolith organs?

Answer 27

• Sensory spot in the wall of the Utricle and Saccule
• Contains otolithic membrane + otoconia (“ear crystals”)
• In the Utricle: the macula is horizontal and detects linear acceleration in the horizontal plane (left to right)
• In the Saccule: the macula is vertical and detects linear acceleration in the vertical plane (up and down)

Question 28

What is the Vestibulo-Ocular Reflex?

Answer 28

• Movement of the Crista Ampullaris is the stimulus for this reflex
• The VOR is responsible for stabilising the gaze by moving eyes in order to compensate for head and body movement -> this fixes the image on the retina for clear sight

Question 29

Which systems regulate Body Balance?

Answer 29

• Visual
• Vestibular (rotation and gravity)
• Proprioceptive (pressure)

Question 30

Which clinical conditions of the ear affect balance?

Answer 30

• Benign Paroxysmal Vertigo (!!!)
• Vestibular Neuritis
• Meniere’s Disease

Question 31

What is the pathophysiology of Benign Paroxysmal Positional Vertigo? (BPPV)

Answer 31

• Loose Otoconia (from the utriculae maculae)
• They move out of the Utricle and into the Semi-circular canals (most commonly, the posterior semi-circular canal), stimulate the cristae ampullaris and provoke Vertigo and Nystagmus

Question 32

What is the test for Benign Paroxysmal Positional Vertigo? (BPPV)

Answer 32

• Dix-Hallpike maneouvre

basically replicating the otoconia moving out of position and stimulating the cristae ampullaris

Question 33

What is the treatment for Benign Paroxysmal Positional Vertigo? (BPPV)

Answer 33

• Epley maneouvre

basically puts the otoconia back into their positions in the otolith organs

Question 34

What are the clinical features of Vestibular Neuritonitis/Acute Labyrinthitis?

Answer 34

• Acute onset of Vertigo, nausea and vomiting
• Rarely hearing loss
• > (if present, can truly be called Labyrinthitis bc it would affect the whole bony labyrinth)

Question 35

What are the causes of Vestibular Neuritonitis/Acute Labyrinthitis?

Answer 35

• Definitive aetiology rarely proven
• Histological evidence points to viral damage of vestibular nerve
• If hearing loss is present: mumps, measles or infectious mononucleosis may be responsible

Question 36

What are the clinical features of Meniere’s disease?

Answer 36

Classic Triad of...
1 - Vertigo
-> unpredictable
-> severe
-> 30mins - 24hrs
2 - Unilateral hearing loss
-> sensorineural in nature
-> usually recovers with time -> usually develops low-grade sensorineural hearing loss
3 - Tinnitus

• Also: often a sensation of “fullness” in the ears
• Episodic -> recurrent attacks
• Episodes can come on in clusters

Question 37

What are the pathophysiology of Meniere’s disease?

Answer 37

• Endolymphatic hydrops
• Endolymph produced by stria vascularis
• Hydrops due to malabsorption of Endolymph in endolymphatic duct and sac

Question 38

What type of Vertigo is present in Migraines?

Answer 38

• Episodic Vertigo (recurrent attacks!)

- > most common cause of episodic vertigo!!!