Hearing and Balance Flashcards
Hearing and balance are both innervated by which cranial nerve ?
Both housed in the ear, innervated by CN CIII:
Chchlea branch convey sound
Vestiular branch conveys head position/motion
In the temporal bone : ___ (outside) and ___ (inside)
In the temporal bone : bony labyrinth (outside) and membranous labyrinth (inside)
_________ ; semicircular duct inside canal
Cochlear duct; semicircular duct inside canal
Cochlear duct attaches to the ____, semicircular ducts attach to the ___, ___ connected to utricle
Cochlear duct attaches to the saccule, semicircular ducts attach to the utricle, saccule connected to utricle
____ in bony labyrinth - like csf and continuous with subarachnoid
Perilymph in bony labyrinth - like csf and continuous with subarachnoid
Blockage of fluid causes ?
Blockage of fluid (like hydrocephalus) causes Meniere’s disease , vertigo , nausice, hearing loss
Describe receptrors (Hair cells), and cranial nerve attached, their location
hair cells (purple) with microvilli extending from top:
Tallest is kinocilium (f?) others are stopped in height - stereocilia
Two tallest microvilli enter gelatinous mass
Each microvilli attached to the next tallest by tip links. : each tip link has ion channel
Microvilli are in endolymph but base of hair cells is in perilymph where synapses to CN VIII
Endolymph and perilymph separated by barrier of tight junctions of cells.
location
6 discrete locations (1 on each base of semicircular disc , 1 on utricle , 1 in saccule 1 stripe that winds cochlear duct.)
What are the components of ear, location ? what are they filled with ?
Outer ear (up to eardrum)
Middle ear (inner eardrum and ossicles)
inner ear (cochlea)
outer eat and middle ear are filled with air
inner ear filled with fluid
air (sounds) have to pass through both to detected.
Describe flow of sound from ear canal to organ of Corti
Sound enter ear canal, vibrates tympanic membrane (eardrum) , vibrates ossicles (alleus -> incus -> stapes) goes through oval window to vestibular to cochlea to organ of Corti
what muscles attached to ossicles ?
Sound transformed though ossicles
2 muscles attache to ossicles:
tensor tympani - innervated by trigeminal
stapedius - innervated by facial
Describe organ of Corti.
Once inside the cochlea the sound waves travel to the organ of Corti (the auditory receptor organ)
Which sits on the basilar membrane
Organ of Corti is a strip of hair cells and support ells . Hair cells are arranged in 2 groups:
3500 inner hair cells : single file
15000 outer hair cells 2-5 wide
what properties of sound must be encoded ?
3 properties of sound must be encoded
intensity - coded by rate of AP firing
location - requires comparison of both ears so happens in CNS
frequency - determined by which part of organ of Corti is most active:
progressively higher frequencies as move from apex to base of cochlea
provide mechanical tuning system that end up .. etc
Hair cells
Inner hair cells are the ____ cells
Outer hair cells are ____ (of basilar membrane travelling waves)
Hair cells
Inner hair cells are the sensory cells
Outer hair cells are amplifiers (of basilar membrane travelling waves)
describe pathway from brainstem to cortex.
CN VIII enters at pontomedullary junction, branches to dorsal cochlear nucleus and central cochlear nucleus
Ascend the lateral lemniscus , the major auditory pathway of brainstem (some cross midline some don’t so get intro from both ways) to the inferior colliculi
From inferior colliculi to the medial geniculate nucleus of the thalamus
From thalamus to primary auditory cortex in a tonotopical fashion
primary auditory cortex is transitive temporal gyrus (Heschel’s gyrus) in the lateral fissure.
Other fibers leave the cochlear nucleus and end in superior olivary nucleus crossing at trapezoid body
use info from both ears to localise sound by measuring tie of arrival of sound.
Tonotopic mapping of pitch in primary auditory cortex (Heschel’s) : Low freq tones are __ and move __ for the high fern tones.
Tonotopic mapping of pitch in primary auditory cortex (Heschel’s)
Low freq tones are lateral and move medially for the high fern tones.
what kinds of hearing damage
Hearing Damage
Conduction - sound doesn’t reach the labyrinth
Sensorineural - damage to hair cells or cochlear nerve fibers of the cochlear nuclei
Audiograms from tests of air conduction and bone conduction of sound can be used to dx which type of loss
bone conduction problem would indicate sensorineural loss
impaired air but preserved bone conduction would indicate conduction loss
Each semicircular canal ends with a bulge - ______
Each semicircular canal ends with a bulge - ampulla
describe how vestibular function work
1 semicircular duct receptors detect angular acceleration of the head
one end semicircular duct has an ampulla
Inside ampulla is a ridge if tissue covers hair cells receptors allied crista
Attached to crista is CN VIII
Gelantinous mass above crista in which stereo cilia project - c u p u l a and extends to the top of the amuplla (spilling in half )
no crista in utricle and saccule , instead have _____
Also embedded in gelantinous mass but this one has crystals in it (______)
no crista in utricle and saccule , instead have macula
Also embedded in gelantinous mass but this one has crystals in it (otoliths)
how Utricle and saccule detect linear acceleration and head position ?
Makes the membrane denser than fluid to when head moves membrane globs to one side and stays there and hair cells are moved and send signal to CN VIII fivers to report new head position
utricle detects acceleration in ____
saccule detects acceleration in ______
Detect linear acceleration
utricle (acceleration in horizontal plane: car ride)
saccule - (acceleration in vertical plane: elevator)
describe the path from ear to cortex
auditory canals to vestibular nuclei on brainstem and to the Cb
Vestibular nuclei to lots of places
Vestibular sense enables us to regulate our posture and coordinate eye and head movement:
so sends projections to spinal cord , Cb
brainstem nuclei of CN III IV VI (eye movement)
visceral autonomic response (sick from roller coaster)
thalamus (VPL) to cortex for propioceptive movement through space
mostly parietal (btw intraparietal and postcentral gyri) which is near body position potion of sensory strip
posterior insula( near auditoy cortex)
Eye movement compensate for changes in head movements.
__________ comes from CN ______ nuclei (eye movement)
Eye movement compensate for changes in head movements.
Vestiblulo-occular reflex (VOR) comes from CN III IV VI nuclei (eye movement)
________ illusions of movement in response to certain orientations of the head.
Vertigo illusions
illusions of movement in response to certain orientations of the head (vertigo)
combined at level of ____ where ___ , ___, and ___ input coverage
if 1 of the 3 sense is impaired , the other two can compensate.
combined at level of vestibular nuclei where visual , somatosensory, and vestibular input coverage
if 1 of the 3 sense is impaired , the other two can compensate.
________ - can balance fine with eye open but when close eyes there is swaying and loss of balance.
Rombeg’s sign- can balance fine with eye open but when close eyes there is swaying and loss of balance.
