Anatomy / Physiology of the Ear, and Physiology and Clinical Aspects of Hearing and Balance Flashcards
Which bones form part of the middle ear?
- The ossicles*
- Malleus (hammer)
- Incus (anvil)
- Stapes (stirrup)
Which bones form part of the inner ear?
- Semicircular canals
- Cochlea
What is the function of the middle ear ossicles?
- 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!!
What structures do sound-waves encounter (in order) when travelling through the middle ear?
- 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
What is the pathophysiology of Otitis Media w Effusion? (AKA “Glue Ear”)
- 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!)
What is the pathophysiology of Otosclerosis?
- 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!)
What structures make up the Organ of Corti?
- Tectorial membrane above
- Cilia on top of (inner and outer) Hair cells
- Basilar membrane below
Describe the hearing mechanism in the Cochlea
- 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
Describe the phrase “Tonotopic Arrangement”
- 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)
How can you assess hearing in the clinic?
- Clinical Testing
(ie. covering pt’s eyes or going behind them while saying words) - Tuning fork tests
- Audiometry
- Objective testing (ie. Tympanometry, OAEs)
What are the different types of Tuning fork tests?
What is the purpose of them?
- Weber’s, Rinne’s
- To differentiate whether the hearing loss is conductive or sensorineural
What is the purpose of a Weber’s test?
- A test of lateralisation
- Tells u in what ear there is hearing loss
How do you interpret the results of a Weber’s test?
- 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
What is the purpose of a Rinne’s test?
- 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
How do you interpret the results of a Rinne’s test?
- Air louder than bone (Rinne’s +ve) = normal or sensorineural hearing loss (false-positive)
- Bone louder than air (Rinne’s -ve) = conductive
Who is pure tone Audiometry used for?
- First-line diagnostic test for pt’s hearing loss
- Older children + Adults
Who is visual reinforcement Audiometry used for?
- First-line diagnostic test for pt’s hearing loss
- Babies!
Who is play Audiometry used for?
- First-line diagnostic test for pt’s hearing loss
- children aged 2-5 years, learning disabilities
What are the different objective hearing tests?
- 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
How is volume and pitch of sound identified in relation to the sound waves?
- 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)
What does a large “air-bone gap” indicate?
Significant conductive hearing loss
What is the management of hearing loss?
- 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)
Who is an open-fit hearing aid used for?
- 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
Which part of the ear controls balance?
The vestibular labyrinth! (inner ear)
Describe the components of the vestibular labyrinth
2 Otolith organs -> contain otoconia which gives them their name of “otolith” organs!
- Utricle: 3 semi-circular canals
- Saccule
What is the function of the Ampullae of the Semi-circular canals?
- 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
What is the role of the macula in the Otolith organs?
- 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)
What is the Vestibulo-Ocular Reflex?
- 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
Which systems regulate Body Balance?
- Visual
- Vestibular (rotation and gravity)
- Proprioceptive (pressure)
Which clinical conditions of the ear affect balance?
- Benign Paroxysmal Vertigo (!!!)
- Vestibular Neuritis
- Meniere’s Disease
What is the pathophysiology of Benign Paroxysmal Positional Vertigo? (BPPV)
- 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
What is the test for Benign Paroxysmal Positional Vertigo? (BPPV)
- Dix-Hallpike maneouvre
basically replicating the otoconia moving out of position and stimulating the cristae ampullaris
What is the treatment for Benign Paroxysmal Positional Vertigo? (BPPV)
- Epley maneouvre
basically puts the otoconia back into their positions in the otolith organs
What are the clinical features of Vestibular Neuritonitis/Acute Labyrinthitis?
- 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)
What are the causes of Vestibular Neuritonitis/Acute Labyrinthitis?
- 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
What are the clinical features of Meniere’s disease?
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
What are the pathophysiology of Meniere’s disease?
- Endolymphatic hydrops
- Endolymph produced by stria vascularis
- Hydrops due to malabsorption of Endolymph in endolymphatic duct and sac
What type of Vertigo is present in Migraines?
- Episodic Vertigo (recurrent attacks!)
- > most common cause of episodic vertigo!!!
