lec 19 auditory system Flashcards
What are sounds?
- audible variations in pressure
- waves have freq/amplitude
What is audible range of sound for humans?
freq ~20 Hz - 20,000 Hz
intensity 1-120 dB
What are the 3 parts of ear?
outer = pinna + external auditory meatus
middle = ossicles, tensor tympani, stapedius, eustachian tube
inner = cochlea, canals, vestibule
What is the function of the pinna?
- vertical localization of sounds
What is the function of external auditory meatus?
- magnifies sound by passive resonance
What are the ossicles?
3 bones of middle ear
- malleus [hammer] - associated with tympanic membrane
- incus [anvil]
- stapes [stirrup] - sits on oval window
What two muscles in the middle ear? function?
tensor tympani - attached to malleus, stretches tympanic membrane
stapedius - associated with stapedius, dampens movement of stapes in + out of oval, mediates acoustic reflex which attenuates impact of loud sounds
What separates outer from middle ear?
tymapnic membrane
What innervates the tensor tympani?
motor root of trigeminal
“three Ts go together. tensor tympani trigeminal}
What is the acoustic reflex?
stapedius shortens chain of ossicles thus dampening stapes movement, protects impact of loud sounds on inner ear
What is function of eustachian tube?
provides air-air conduit between nasal passage and middle ear
- open during yawning, chewing, swallowing to equilibrate air pressure in middle ear with external
What is difference between perilymph and endolymph?
perilymph = in bony cochlear, high K low Na, more aqueous endolymph = in membranous cochlear, high K low Na, more viscous
How many turns to cochlea?
2 3/4
What connects the vestibule to the subarachnoid space?
perilymphatic duct for perilymph drainage
What are the 3 compartments in the bony cochlea?
- scala vestibuli = in
- scala tympani = out
- scala media = membrane middle endolymph
What are the 3 turns of the cochlea?
- basal, middle, apical
What is the helicotrema?
apex of the cochlea
- where ripple wave loops back around and goes out
Where are receptors for hearing located in cochlea?
the receptors are hair cells within organ of corti that rests on basilar membrane of scala media [on the tympanic side]
What are the names of the two membranes surrounding scala media?
vestibular membrane on side of scala vestibuli
basilar membrane on side of scala tympani
What is difference inner and outer hair cells?
inner = 1 row, make up 95% of the auditory nerve
outer = 3 rows, receive input from superior olive, sharpen sound frequency, protect hair cells from harmful noise, produce otoacoustic emission
*naming inner vs outer is with respect to central bone of cochlea [modiolus]
How does hair bundle activate? inactivate?
activate = depolarization when bundle of sterocilia tilt toward kinocilium
inactivate = hyperpolarization when bundle of stereocilia tilt away from kinocilium
How is sound produced in inner ear?
- traveling sound wave transmitted from outer ear through tympanic membrane to oval window then through perilymph of scala vestibuli/tympani, cause differential movement of basilar membrane and tectorial membrane, causing inner hair sterocilliary bundles to bend –>
What is the difference between basilar membrane at base and apex?
apex: wider, more flexible, lower tones
base: narrower, stiffer, higher tones
What is the function of outer hair cells?
- amplify movement of basilar membrane in response to low intensity sound
- make sound when they change height = otoacoustic amissions
What part of ear is vulnerable to aminoglycoside antibiotics?
outer hair cells
Where are cell bodies of auditory nerve fibers located?
spiral ganglion = within the bone of the spiral lamina of choclea
What is path of bipolar auditory neurons from the spiral ganglion to the auditory cortex?
- go through internal auditory meatus then form CN 8
- enters the brainstem at cerebello-pontine angle
- terminate in cells on lateral medulla = ipsilaterall cochlear nuclei
- from cochlear nuclei become bilateral –> go to superior olives, inferior colliculi, then medial geniculate bodies
If patient has unilateral hearing deficit where must the problem be along the auditory path?
must be in cochlear nucleus or auditory nerve or in the ear itself because everything else if bilateral
What is the lateral lemniscus?
the fiber bundle output of the superior olive and cochlear nuclei
What is the auditory nucleus in the thalamus?
medial geniculate nucleus [MGN]
What structure is responsible for sound localization in the horizontal plane?
superior olive [due to its bilateral input]
-measures interaural intensity and timing difference to localize horizontally
What is the olivocochlear bundle?
projects from superior olive to outer hair cells
- important pathway for selective auditory attention, control of noise masking, and protection from loud noise
Where is the medial geniculate nucleus in the thalamus?
hangs off the bottom back of the thalamus
What is the primary auditory cortex?
heschl’s gyri on superior temporal gyri
How is the primary auditory cortex organized?
tonotopically
- low frequency in anterior
- high frequency in posterior
isofrequency bands = laterally oriented strips of cells that hare same characteristic frequencies
What is function of wernicke’s area? location with respect to primary auditory cortex?
higher order auditory cortex area
important for speech recognition and comprehension
- caudal to primary auditory cortex on language dominant hemisphere
