Week 3 - Fitzakerely (Hearing & Balance) Flashcards
As the Semicircular Canals are “motion detectors”, what does a lesion induce the sensation of?
Spinning
(Detect head rotation –> angular acceleration)
As the Otolith Organs (utricle and saccule) are “gravity detectors”, what does a lesion induce the sensation of?
Tilting
(Detect gravity –> linear acceleration)
What system acts as the postural signal reference?
Vestibular system
Where are hair cells found in the semicircular canals?
surface of the ampullary crest
(piece of bone that protrudes into the ampulla)
What is the gelatinous matrix that the stereocilia of type I & II vestibular hair cells are embedded in called?
Cupula
How are all of the sterociliary bundles in the ampulla oriented?
In the same direction!
What pair of semicircular canals are tested in the caloric test?
Horizontal canals
What pair of semicircular canals are tested in the Dix-Hallpike test?
one pair of anterior/posterior canals
What happens in the semicircular canals when you tilt your head forward (what depolarizes/hyperpolarizes)?
Depolarization of Anterior Canals
&
Hyperpolarization of Posterior Canals
What happens in the semicircular canals when you tilt your head forward (what depolarizes/hyperpolarizes)?
Depolarization in the Left Horizontal Canal
&
Hyperpolarization in the Right Horizontal Canal
What is labyrinthitis? What are common symptoms?
Inflammation of the inner ear
- Symptoms:
- vertigo
- temporary hearing loss
- tinnitus
- N/V
Where are the cell bodies of the primary afferent fibers of the central auditory pathway?
Spiral Ganglia
&
Vestibular Nerve (Scarpa’s) Ganglia
What are the 6 steps in the Auditory Pathway?
- Hair cells –> Auditory Nerve
- Cochlear Nuclei –> Trapezoid body
- Superior Olivary Complex –> Lateral Lemniscus
- Inferior Colliculus –> brachium of IC
- Medial Geniculate Nucleus –> Internal Capsule
- Primary Auditory Nucleus (superior temporal gyrus)
What projections are bilateral in the Auditory Pathway?
All central projections, starting with the trapezoid body.
(Cochlear nucleus projects both ipsilaterally and contralaterally)
What are the two important reflex loops from the superior olivary complex?
- Back to the cochlear hair cells - allows loud sounds to modify the vibration of the basilar membrane
- OHC - efferent synapses on cell body
- IHC - efferent synapses on afferent fibers
- Acoustic Reflex - negative feedback loop to the middle ear muscles
- Trigeminal Motor Nucleus –> Tensor Tympani via CN V3
- Facial Motor Nucleus –> Stapedius via CN VII
What are the 4 steps of the Vestibular Pathway that is the afferent pathway for perception?
- Hair Cells (SC/Otolith) –> Vestibular Nerve
- Superior/Lateral Vestibular Nuclei –> medial lemniscus
- Ventroposterior Nucleus –> Internal Capsule
- Vestibular Cortex (debated location)
What are the 4 steps of the Vestibular Pathway responsible for control of head/neck/upper limb position in response to movement?
- Hair cells (Semicircular Canals & Otolith organs)
- Vestibular Ganglion/Nerve
- Lateral/Medial/Inferior Vestibular Nuclei
- Vestibulospinal Reflexes
- Lateral Vestibulospinal Tract (LVST)
- Medial Vestibulospinal Tract (MVST)
- Limb & Trunk (via LVST) OR Upper Back & Neck (via MVST)
What are the four steps of the Vestibular Pathway that are responsible for control of eye position relative to head position (VOR)?
- Hair Cells (Semicircular Canals & Otolith Organs)
- Vestibular Nerve/Ganglion
- Superior/Medial Vestibular Nuclei
- Medial Longitudinal Fasciculus (MILF)
- Oculomotor Nucleus/Abducens Nucleus/Trochlear Nucleus
- Superior, medial, and inferior rectus via CN III
- Lateral Rectus via CN VI
- Superior Oblique via CN IV
What is the purpose of the Vestibulospinal reflexes?
maintaining the head in an upright position
What is the purpose of the Lateral Vestibulospinal system?
Compensate for tilts and movements of the body during postural changes
What is the purpose of the Medial Vestibulospinal system?
Stabilize head position while walking
In sound localization processing, does the lateral or medial superior olive interpret whether a sound is louder in one ear?
Lateral Superior Olive
(high frequencies –> “Intensity Pathway”)
In sound localization processing, does the lateral or medial superior olive interpret whether a sound reaches one ear first?
Medial Superior Olive
(low frequencies –> “Time Pathway”)
What is the only way to have an ipsilateral hearing loss?
Peripheral lesion
(Cochlea, Auditory Nerve, or Cochlear Nucleus)
What type(s) of deficiencies constitute a Central Auditory Processing Disorder (CAPD)?
- Deficiency in:
- Sound localization & lateralization
- Discrimination
- Pattern recognition
- Temporal aspects of sounds
- Ability to deal with degraded and competing acoustic signals
- “Cocktail Party Effect”
What type of hearing loss does amplification help combat?
Sensorineural
In classic posterior canal BPPV, what type of nystagmus indicates that the posterior canal is affected?
Upbeating nystagmus
(more rare = downbeating –> anterior canal)
In a normal ear, the middle ear pressure equals the atmospheric air pressure due to the function of what?
Eustachian tube
What is the purpose of the Rinne Test?
determination of conductive hearing loss
(tuning fork on mastoid process)
***Due to the amplification provided by the middle ear, in a normal person: air threshold is less than bone threshold (louder through air vs. bone)
What is the purpose of the Weber Test?
Determination of a conductive vs. a sensorineural hearing loss.
(base of tuning fork placed on top of head)
*Normal = equally lound in both ears
**Conductive = louder in affected ear
***Sensorineural = louder in the normal ear
What are common causes of conductive hearing loss?
- ruptured eardrum
- intratympanic fluid –> otitis media
- otosclerosis
What does a normal audiogram look like?
Air conduction = Bone conduction
both thresholds are about 0 Hz
What does an audiogram of conductive hearing loss look like?
Increased threshold in air conduction:
about 50 dB loss
Conduction block increases the mass (high frequencies) or the stiffness (low frequencies) or both.
*Stiffness (low frequencies) usually affected 1st.
What does an audiogram of sensorineural hearing loss look like?
Increase in thresholds and/or loss of ability to transduce specific frequencies due to damage to the cochlea, auditory nerve, or cochlear nucleus.
- Affects both air and bone conducted stimuli.
- Both air/bone curves exhibit a threshold shift in the affected frequency range.
What are common causes of sensorineural hearing loss?
- Noise (hair cell/stereocilia damage)
- Genetic defects
- Ototoxic drugs (aminoglycoside antibiotics)
- gentamicin
- amikacin
- Loop diuretics
- furosemide
What fluid does the bony (osseous) labyrinth contain?
Na+ rich PERILYMPH
What fluid does the membranous labyrinth contain?
K+ rich ENDOLYMPH
What area of the osseous labyrinth contains the oval and round windows?
Vestibule
What canals extend from the vestibule?
- 3 semicircular canals
- Cochlea
- Vestibular aqueduct
- Cochlear aqueduct
What happens in a rupture of the bony layrinth?
Causes CSF flow through the cochlear aqueduct –> Perilymphatic Fistula
(no membranous labyrinth in the cochlear aqueduct)
What does it mean that the membranous labyrinth is completely enclosed?
There are NO connections between the spaces containing endolymph and those containing perilymph.
What are the four main components of the Membranous Labyrinth?
- Cochlear duct (= scala media)
- Saccule
- connected to the cochlear duct via ductus reuniens
- Utricle
- connected to the saccula via endolymphatic duct
- Semicircular canals
What are the 6 areas within the inner ear that contain the sensory receptor hair cells?
- 3 cristae ampullaris
- 1 in each semicircular canal
- 2 maculae
- 1 in the saccule
- 1 in the utricle
- 1 organ of corti
- in the cochlea
What is the innervation of the inner ear?
- Vestibulocochlear Nerve (CN VIII)
- Sensory afferents from hair cells (Type I) –> brainstem
- Brainstem –> Motor efferents to hair cells (Type II)
How does the Vestibulocochlear Nerve (CN VIII) exit the cranial vault?
Through the internal auditory meatus.
(exits with Facial Nerve CN VII)
What are the four branches of the Vestibulocochlear Nerve (CN VIII)?
- Auditory (cochlea)
- Superior Division (utricle, Anterior & Lateral SC)
- Inferior Division (saccule)
- Posterior Division (Posterior SC)
What compartment of the cochlea do vibrations ascend to the apex?
Scala Vestibuli
What compartment of the cochlea do vibrations descend to the base of the cochlea?
Scala Tympani
What membrane is the Organ of Corti located on?
Basillar membrane
In a comatose patient what part of the VOR is present and absent?
Present: Pursuit (brainstem)
Absent: Saccade (cortex)
In a patient that is brain dead, what part of the VOR will be present and absent?
BOTH the PURSUIT and SACCADE will be ABSENT.
What produces the endolymph and the endocochlear potential?
Stria Vascularis
(contains many of the same ion transporters as the kidney, that’s why drugs that affect renal function are often ototoxic!)
What part of the cochlea are high frequencies transduced?
Base
What part of the cochlea are low frequencies transduced?
Apex
What determines the absolute threshold of hearing at each frequency?
The Middle Ear
What are the components of the 3 neuron arc in the Vestibulo-ocular Reflex (VOR)?
- Hair cell/Vestibular Nerve (CN VIII)
- Vestibular Nuclei
- Cranial Nerve Motor Nuclei
What causes vibration at the oval window?
- Vibration of the tympanic membrane
- Malleus and Incus pivot
- Stapes footplate vibrates oval window
What produces cerumen in order to protect the tympanic membrane?
Large modified APOCRINE GLANDS deep in the dermis of thee external auditory meatus
