Auditory & Vestibular Systems Flashcards
What are the two divisions of CN VIII and what are their functions?
Cochlear - sound
Vestibular - head position and movement
Both divisions of CN VIII innervate highly specialized organs with mechanoreceptors called ___ ___ that sense different mechanical stimuli.
hair cells
Where are auditory and vestibular receptors located?
In the walls of membranous inner ear structures embedded in the temporal bone, suspended in a bony tube
What CN innervated auditory and vestibular receptors?
CN VIII
The ___ labyrinth contains the ___ is coiled and extends into an enlarged ___ that has 2 ___ canals attached.
bony; cochlea; vestibule; semicircular
What is the tube that is suspended in and follows the contours of the bony labyrinth?
membranous labyrinth
What parts of the membranous labyrinth are enclosed in the cochlea and semicircular canal?
cochlear duct is in the cochlea
semicircular duct is in each semicircular canal
What are the two vestibule enlargements of the membranous labyrinth?
utricle and saccule
T/F. The saccule is attached to the semicircular ducts.
False, the utricle is attached to the semicircular ducts. The saccule is connected to the cochlear duct and utricle.
What does perilymph fill?
the bony labyrinth
Perilymph is similar in composition to ___ and is continuous with ___ space thru the cochlear ___.
CSF; subarachnoid; aqueduct
___ fills the membranous labyrinth and is similar in compostion to ___ fluid.
Endolymph; intracellular (potassium-rich/sodium poor)
T/F. Endolymph is closed off from the outside but all parts of the membranous labyrinth communicate with each other.
True.
What is the function of the tight junctions in hair cells?
Tight junctions in hair cells (and other cells)
- keep perilymph and endolymph separate
- establishes voltage and concentration gradients needed for transduction
What produces endolymph? How is it resorbed?
produced by specialized cells in the cochlea
Resorbed in endolymphatic sac
Obstruction of flow results in swelling of which labyrinth?
membranous
A patient presents with transient attacks of vertigo, nausea, hearing loss and tinnitus (ear ringing). The cause is unknown and likely multiple. What condition is this?
Ménière’s disease
T/F. Hair cells are auditory and vestibular receptor cells.
True.
Hair cells are named for specialized ___ that project into ___ at one end of cell and the other end has processes of CN ___.
microvilli; endolymph; VIII
Hair cell microvilli are also known as what?
stereocillia
How are stereocillia arranged?
in graduated rows with the tallest toward one side
Where do you find kinocilium? Where are they not found?
Kinocilium are near tallest stereocillia in semicircular ducts, utricle, and saccule.
Cochlear hair cells lack kinocillia.
T/F. Hair cells are grouped into 5 discrete areas.
False, it’s 6.
What are the tips of kinocilum and the tallest stereocillia embedded in?
specialized mass of gelatinous material
How is the receptor potential transduced?
movement of gelatinous mass relative to hair cells cause deflection of sterocillia
In the organ of corti, the labyrinth part of the ___, the gelantinous material is the ___ ___ and the stimulus tranduced is ___.
Cochlea; tectorial membrane; sound
In the cristae, the labyrinth part of the ___ ___, the gelantinous material is the ___ and the stimulus transduced is ___ acceleration.
semicircular ducts; cupula; angular
In the maculae, the labyrinth part of the ___ and ___, the gelatinous material is the ___ membrane and the stimulus transduced is ___ acceleration.
utricle; saccule; otolithic; linear
T/F. Hair cells are mechanosensitive.
True.
T/F. Deflection towards the tallest stereocillia depolarizes hair cells.
True
Deflection away from the tallest stereocillia ___ hair cells.
hyperpolarizes
What happens if the hair cells are deflected in a perpendicular plane?
It has no effect, no receptor potential results
T/F. The outer and inner ear convey airborne sound vibrations to fluid-filled inner ear.
True.
What moves perilymph?
stapes
T/F. The tympanic membrane is 15X the size of stapes so stapes vibrations have less force/unit area.
False, they have more force/unit area.
How is the sound of ones own voice blocked?
The Stapedius pulls stapes away from oval window of the cochlea, stiffening the ossicular chain.
The ___ pulls stapes away from ___ window of the cochlea, stiffening the ___ chain. This in innervated by CN ___.
Stapedius; oval; ossicular; VII
How is the sound of chewing blocked?
Tensor tympani pulls the malleus in toward the middle ear, stiffening the ossicular chain.
___ ___ pulls the malleus in toward the middle ear, stiffening the ___ chain. This is innervated by CN ___.
Tensor tympani; ossicular;V
What does spasm of the stapedius cause?
Spasm can cause clicking sound when speaking
What does spasm of the tensor tympani cause?
Spasm cause tinnitus at low frequency
What is a perilymphatic space, continuous with vestibule?
Scala vestibuli
What area of the cochlea contains endolymph?
scala media
What is a perilymphatic space, ends blindly at round window?
Scala tympani
The ___ has spongy bone at its core and houses the ___ ganglion, cell bodies of primary ___ fibers. These fibers collect and form ___ division of VIII.
modiolus; spiral; afferent; cochlear
What is a strip of cells that rest on the basilar membrane?
Organ of Corti
Which hair cells are not attached to the gelatinous tectorial membrane and are stimulated by endolymph movement across the stereocilia?
inner hair cells
T/F. Outer hair cells have sterocillia inserted into the tectorial membrane.
True.
T/F. Inner hair cell vibrations in basilar membrane causes oscillations in membrane potential of hair cells.
False, Outer hair cells do this.
With the ___ ducts, vibrations transmitted to ___in the scala vestibule and energy is transmitted to scala ___, deforming cochlear duct slightly and stimulating receptors within.
auditory; perilymph; tympani
What causes a pressure pulse in the scala vestibuli that leads to a traveling wave of deformation in the basilar membrane?
The stapes
T/F. Mechanical properties of basilar membrane differ along its length, so a traveling wave reaches peak amplitude at a location that depends on stimulus frequency.
True.
“___ ___” of basilar membrane is the beginning of tonotopic organization of auditory system. Particular frequencies are mapped to specific locations of relay nuclei and cortex.
Mechanical tuning
When is a cochlear implant used?
when cochlear hair cells damaged, but VIII endings are intact
How does a cochlear implant work?
Place electrodes in round window into scala tympani so different electrodes are placed at different points along basilar membrane. Electronics stimulate VIII endings at appropriate tonotopic levels.
What pathway is the primary ascending auditory pathway that carries information from both ears?
Lateral lemniscus
The CNS auditory processing mostly consists of fibers from what nucleus?
dorsal cochlear nucleus
Where is the primary auditory cortex located?
in the transverse temporal gyri of Heschl on the superior surface of the temporal lobe.
How are gyri of the primary auditory cortex different from other temporal gyri?
they run mediolaterally rather than front to back
T/F. Brodmann areas 41 and 42 are part of the primary auditory cortex.
True.
T/F. Sound from left reaches right ear before left ear and is more intense in left ear.
False, Sound from left reaches LEFT ear before RIGHT ear and is more intense in left ear.
What structure is important to sound localization and receives fibers from bilateral cochlear nuclei?
superior olivary nucleus
Fibers traveling through the superior olivary nucleus cross in the midline through what structure?
trapezoid body
What are the two subnuclei of the superior olivary nucleus?
medial (arrival time comparison) and lateral
What is a plot of data that measures subject’s threshold hearing for a series of pure tones thru earphones (air conduction) and vibration (bone conduction)?
audiogram
If the audiogram process prevents sound from reaching the labyrinth, what condition is caused?
conductive hearing loss
If the audiogram process damages hair cells or cochlear nuclei, what condition is caused?
sensorineural hearing loss
___ conduction needs intact outer, middle and inner ear, whereas ___ conduction bypasses the ear as skull can transmit sound waves to fluids in labyrinth.
Air; bone
Normal hearing by ___ conduction but not by ___ suggests a ___ hearing loss and may be due to middle ear infections.
bone; air; conductive
In patients with bilateral otitis media, which type of conduction is greater, air or bone?
bone
T/F. The vestibular division of CN VIII detects linear and angular accleleration.
True.
What is the function of the vestibular division of CN VIII?
It regulate posture, coordinate eye and head movements and maintains orientation in response to movements.
Receptors in semicircular ducts detect ___ acceleration of the head.
angular
T/F. Each semicircular duct communicates at only one end of the utricle. One end of each duct has an ampulla and contains crista.
False, each semicircular duct communicates at BOTH ends with the utricle. One end of each duct has an ampulla and contains crista.
Define crista.
Transversely oriented ridge with hair cells
The crista contains ___ in gelantinous mass and is covered by a ___ that extends across the ___.
stereocillia; cupula; ampulla
How are hair cells aligned in the semicircular ducts?
All hair cells are aligned so kinocilia face in same direction.
Deflection of the ___ in one direction leads to increased firing in ___ fibers.
cupula; afferent
T/F. Deflection of the cupula rotates the semicircular duct in an axis parallel to it.
False, in an axis perpendicular to it.
Explain the how rotation deflects the cupula.
As rotation begins endolymph lags behind due to inertia and deflects cupula stimulating hair cells. If rotation maintained, endolymph will catch up (Not detected, not a big deal). Rotation stops, endolymph still moving.
Due to endolymph moving during rotation, each canal responds best to changes is speed of rotation in a given plane known as ___ acceleration.
angular
What type of acceleration do receptors of the utricle and saccule detect?
linear
In the utricle, the macula is ___ when the head is upright and the stereocillia face ___.
horizontal, upward
In the saccule, the macula is ___ when the head is upright and the stereocilia face ___.
vertical; lateral
What motion does the utricle detect? saccule?
Utricle: Detects forward-backward & side-to-side
Saccule: Forward-backward, up-down
What has a gelatinous membrane of the macula that contain calcium carbonate crystals, otoconia, otoliths and makes the membrane denser than endolymph?
Otolithic membrane
Where are the primary afferent cell bodies of vestibular projections?
Vestibular (Scarpa’s) ganglion in internal auditory canal
The peripheral processes synapse on the endings of ___ cells and the central processes travel to vestibular nuclei of the ___ medulla and ___ pons. Some travel to the cerebellum (via the ___ body) and end in the ___.
hair; rostral; caudal; juxtarestiform; nodulus
T/F. There are five vestibular inputs and each semicircular duct and macula has its own pattern of termination in these nuclei and connections.
False, there are FOUR vestibular inputs (inferior, medial, lateral, and superior) and each semicircular duct and macula has its own pattern of termination in these nuclei and connections.
What do vestibular projections regulate?
posture, coordinated eye and head movements
T/F. Vestibular projections include the spinal cord, nuclei of III, IV & VI and cerebellum.
True
The spinal cord, nuclei of III, IV & VI and the cerebellum all project to the ___ (ipsilateral/contralateral) vestibular nuclei.
contralateral
From the vestibular nuclei, vestibular projections travel through the thalamus (___) (VPM/VPL) to the ___ in the parietal lobe of the cerebral cortex to provide conscious awareness of movement in space.
VPL; insula
Some vestibular projections travel to visceral nuclei of the brainstem. Why?
to adjust cardiovascular system for lying down-standing up and seasickness
The lateral ____ tract arises from the lateral nucleus down to the lateral funiculus and sends ___ projections to ___ antigravity muscles to mediate postural changes to accommodate for ___ in body.
vestibulospinal; excitatory; ipsilateral; tilts
When a person places there head to a bat and spins around in circles in place they are ___ (increasing/decreasing) the activity of the lateral vestibulospinal tract.
increasing
The medial ___ tract arises from the medial nucleus and extends to the ___ ___ via ___ to stabilize head movements when one walks and coordinate head and eye movements.
vestibulospinal; cervical cord; MLF
T/F. The vestibular system works to prevent images from moving on the retina.
True.
What is part of the afferent limb of the vestibuloocular reflex? efferent limb?
VIII, vestibular division
III, IV & VI
T/F. The interneuronal connects the vestibular nuclei to MLF to III, IV, VI and reticular formation.
True.
How does the vestibuloocular reflex responds when you spin to the left?
Left semicircular duct excited (right duct hyperpolarized)
Right lateral rectus and left medial rectus muscles contract
Left lateral rectus and right medial rectus inhibited
How is nystagmus created?
If VOR can’t compensate for head movements, it is interrupted by very rapid eye movements in the opposite direction
Back and forth eye movements with a rapid phase in one direction and a slow phase in the other
Can be normal (watch telephone poles out the train window) or pathologic
What makes the cupula senstitve to gravity?
Alcohol makes the cupula sensitive to gravity
How does alcohol affect the cupula?
Some conditions alter relative densities of cupula and endolymph making semicircular ducts sensitive to gravity
As blood alcohol ↑, EtOH leaves capillaries, infiltrates cupulae, density ↓ relative to endolymph positional nystagmus results
As blood alcohol ↓, EtOH leaves cupulae first, become more dense than endolymph, more nystagmus evident but in opposite direction
Also creates Illusion of movement (positional vertigo) in response to certain head positions due to EtOH
What three systems work together to produce sense of orientation and movement?
vestibular, proprioceptive and visual systems.
If one is defective the others compensate
What system will compensate if the vestibular or somatosensory function is lost?
vision
What is a Romberg’s sign?
Test by asking patient to close their eyes and may sway or lose balance
