3. Auditory System Flashcards
external ear:
function and components
- fxn: collect and transmit sounds
- components
- auricle: outer ear; shape to collect sound
- external auditory meatus: transmitting sound
- tympanic membrane: transform sound wave to mechanical vibration
middle ear:
fxn and components
- fxn: transmit and amplify sound signal
- components:
- malleus, incus, stapes
- middle ear cavity
- oval window
- round window
inner ear:
function and components
- fxn: transforms sound to electric signals
- components:
- scala vestibuli
- scala tympani
- cochlea duct or scala media
which 2 small mucles are important in protecting the ear?
- Tensor tympani muscle: innervated by trigeminal nerve (CN V)
- Stapedius muscle: connected to stapes; inn. by facial nerve
malleus, incus, and stapes correspond with which shapes?
- malleus = hammer
- incus = anvil
- stapes = stirrups
which inner ear structure contains perilymph?
contents of perilymph?
- scala vestibuli
- low potassium, high sodium (similar to ECF)
which inner ear structure contains endolymph?
contents of endolymph?
- cochlear duct/ or scala media
- high potassium, low sodium
where is the helicotrema found?
at the apex of the cochlea (curling structure)
which type of hair cells receive the majority of spiral ganglion innervation?
- 90% of spiral ganglion innervate Inner hair cell; as many as 20 spiral ganglion per 1 inner hair cell
- whereas only 10% of spiral ganglion innervate the 3 outer hair cells; 1 spiral ganglion can cover 12 outer hair cells
what supports hair cells? what is the function?
hair cells are supported by phalangeal (supportive) cells –>
which act to “stiffen” the superior surface of the organ of corti
where are the 1st order neurons in audition?
cell bodies in the modiolus (spiral ganglion neurons);
cell body is in the cochlea –> sends the process to the hair cells
process of inhibition of hair cells
- stereocilia is deflected AWAY from longer stereocilia
- hair membrane depolarizes
- afferent nerve fibers are not stimulated
mechanism for excitation of hair cells?
- stereocilia deflected TOWARDS the longer stereocilia
- results in influx of K+ ions
- hair cell membrane depolarizes
- influx of calcium ions
- then NTs are released –>
- afferent nerve fibers are stimulated (excitation)
where is there tonotopic localization?
in organ of corti
which type of frequency sounds are found at the helicotrema?
lower frequency tones
which type of frequency sounds are found at the base/ closer to middle ear?
high frequency sounds
what movement causes the difference in sound frequencies?
how?
the basilar membrane oscillation allows for diff’t frequencies;
- the base (closer to middle ear) is more stiff/narrow, so higher frequency oscillations will occur here
- whereas the apex/helicotrema is floppy/wide/elastic –> lower frequency stimulation/tone
path of axons from hair cells?
- hair cell axons that are excited –>
- travel from spiral ganglion –>
- via cranial nerve 8 (vestibulocochlear) –>
- to cochlear nucleu –>across midline to
- superior olivary nucleus –> ascends to inferior colliculus –>
- via brachium of inf. colliculus –> medial geniculate nucleus —>
- via auditory radiation –>
- to transverse temporal gyrus of heschi
- into the medulla
where are the cochlear nuclei found?
cochlear division (CN VIII)
the dorsal & ventral cochlear nuclei are found in the medulla
where do cochlear axons synapse?
on the ventral and dorsal cochlear nuclei
w/in the medulla
CC: sxs of lesion of nerve or cochlear nuclei?
deafness
in coronal section, which cochlear nuclei is more inferolateral?
also identify where 4th ventricle would be
ventral nuclei
4th ventricle is medial, empty white space
why would there not be deafness with a unilateral lesion above the cochlear nuclei?
there are a lot of bilateral projections above the cochlear nuclei –>
so it would be able to compensate
where do the cochlear nuclei travel to as they ascend?
to the caudal pons;
specifically the:
- Superior olivary nucleus FIRST
- Lateral lemniscus –> fibers to LL ascend from SON
- Trapezoid body –> fibers from SON decussate/cross over midline through trapezoid body
would a unilateral lesion in the Lateral Lemniscus, Trapezoid body, or Superior olivary nuceli cause deafness?
no, bc there are bilateral projections at multiple sites in the brainstem
How do auditory axons travel from the superior olivary nucleus?
can travel via lateral lemniscus –>
- either continue ascending the brainstem thru cerebral crus to the inferior collilulus, OR
- synapse at nucleus of lateral lemniscus, and travel across the commissure of lateral lemniscus –> caudal mibdbrain
describe pathway from midbrain to thalamus?
the interior colliculus of the caudal midbrain –>
to the medial geniculate nucleus in the thalamus
where does the medial geniculate nucleus of the thalamus project to?
the primary auditory cortex
(aka transverse temporal gyri)
describe the tonotopic organization of the auditory cortex?
- medial side of auditory cortex = high frequency sounds (base)
- lateral side of auditory cortex = low frequency sounds (apex/helicotrema)
where are low frequency sounds found
(w/ regards to tonotopic organization)
lateral side of auditory cortex = low frequency sounds from the apex/helicotrema
which gyri contain the primary auditory cortex?
transverse temporal gyri;
information from here goes to unimodal –> then heteromodal association cortex
tone:
define
frequency; can be high or low
what affects how loud or quiet a sound is?
the amplitude of sound;
i.e. differential firing of afferent fibers
where does sound localization occur?
what does it require?
occurs in superior olive nucleus
requires information from both ears to be able to localize the sound
where do unilateral lesions occur to produce hearing loss?
*but not higher than the cochlear nuclei
- cochlear nuclei
- CN 8 (vestibulocochlear nerve)
- cochlea
a unilateral lesion in the pons, midbrain, or cortex would not produce deafness — why?
due to bilateral projections at multiple sites in the brainstem
superior olivary nuclei:
pathway and function
- project back to cochlea to inhibit auditory nerve terminals on hair cells
- regulates hair cell sensitivity –> regulating selective attention to certain sounds by affecting olivococlear efferent fibers
conductive hearing loss:
define, and possible causes
- (sound transmission is the problem; issue w/ outer or middle ear, or TM)
- causes incl:
- foreign bodies in external acoustic meatus
- perforated tympanic membrane
- otitis media
- otosclerosis
- cholesteatoma
otosclerosis:
define
overgrowth of bones around stapes; if bones are stuck, we can’t hear
cholesteatoma:
define
overgrowth of desquamated keratin debris w/in middle ear cavity;
preventing sound transmission
sensorineual hearing loss:
define and causes
- in which the root cause lies in the inner ear or sensory organ (cochlea and associated structures) or the vestibulocochlear nerve (cranial nerve VIII)
- causes incl:
- congenital hearing loss -genetic mutations, developmental insults
- acquired hearing loss
- noise-induced hearing loss
- aging-related hearing loss
- lesions in auditory pathway
noise-induced hearing loss:
define
types of hearing loss damage to
sterociliated cells in organ of corti, loss of high frequency hearing first
Aging related progressive bilateral/symmetric sensorineural
hearing loss:
define
often of higher frequencies due to the destruction of
hair cells at the cochlear base.
which 2 tests can be used to distinguish conductive vs. sensory neural hearing loss
- Rinne: air conduction –>and then placing on temporal bone to see if you hear the sound through the bone conduction
- Weber: place tuning fork on midline of forehead; sound is conducted through temporal bone; ask where they hear the sound,
bone conduction:
define
Sound vibration can be transmitted through temporal bone vibration to inner ear, less effective than air conduction
air conduction:
define
Sound transmission through tympanic membrane vibration and ossicle movement, more effective than bone conduction
which is more effective?
air or bone conduction?
air conduction
results of weber and rinne tests for:
conductive hearing loss
- Weber: localizes to AFFECTED ear
- Rinne: abnormal (BC > AC)
results of Weber and Rinne tests for:
sensory neural hearing loss
- Weber: localizes to UNAFFECTED ear
- Rinne: normal (BC < AC), w/ AC being more effective
