Auditory System

Question 1

is the outer inner or middle ear air filled? water filled?

Answer 1

outer and middle ear are air filled
inner ear is water filled

Question 2

what are the components of the external ear and what does it mainly do?

Answer 2

auricle, external auditory meatus and the tympanic membrane

the external ear collects and transmits sounds

Question 3

what is the main purpose of the tympanic membrane?

Answer 3

transform sound waves to mechanical vibrations

Question 4

what are the three parts/layers of the tympanic membrane?

Answer 4

1. skin of the external auditory meatus
2. connective tissue with a core of radially and circularly arranged collagen fibers
3. mucous membrane of the middle ear

Question 5

what are the components of the middle ear and what is its main purpse?

Answer 5

• malleus
• incus
• stapes
• middle ear cavity
• oval and round window
• tensor tympani muscle and stapedius muscle

transmit and amplify sound signals

Question 6

what is the main purpose of the tensor tympani and stapedius muscles?

Answer 6

attenuation of sound transmission

Question 7

what are the components of the inner ear and what is its main purpose?

Answer 7

• scala vestibuli
• scala tympani
• cochlear duct and scala media

transformed sound to electrical signal

Question 8

what is at the center of the boney cochlea and what does it contain?

Answer 8

boney modiolus

perikarya of the spiral ganglion

Question 9

what is in the center of each turn of the cochlea and what does it seperate?

Answer 9

the membraneous cochlear duct (scala media)

which separates the scala vestibuli and the scala tympani

Question 10

how do you know you are a the apex of the cochlea?

Answer 10

the membraneous cochlear duct ends blindly
the scala vestibuli and scala tympani become continuous at the helicotrema

Question 11

what does the organ of corti do and where is it located?

Answer 11

rests on the basilar membrane and protects the scala media

Question 12

hair cells are supported by what and what do they do?

Answer 12

phalangeal (supportive) cells that help stiffen the superior surface of the organ of corti

Question 13

the one inner hair cell is innervated by how many spiral ganglions? 10 outer hair cells?

Answer 13

20 spiral ganglion neurons
1 spiral ganglion neurons

Question 14

what is happening if there is no stimulation of a hair cell?

Answer 14

• stereocilia are deflected away from the longer stereocilia
• hair cell membrane hyperpolarizes
• afferent nerve fibers of spiral ganglion neurons are not stimulated

Question 15

what happens during stimulation of a hair cell?

Answer 15

• stereocilia are deflected towards the longer stereocilia
• influx of K+ ions
• depolarization of the hair cell membrane
• influx of Ca2+ ions
• neurotransmitters are released
• afferent nerve fibers of spiral ganglion neurons are stimulated

Question 16

the tonotopic localization in the organ of corti provides what?

Answer 16

higher frequencies are detected near the middle ear
lower tones are detected closer to the helicotrema

Question 17

briefly explain the auditory pathway

Answer 17

cochlea —> cochlear nerve —-> cochlear nuclei in medulla junction—-> crosses over to the superior olivary nucleus in pons (lateral lemniscus) ——> inferior colliculus of midbrain (synapse occurs here) —–> medial geniculate nucleus in the thalmus —–> transverse temporal gyrus (primary auditory cortex)

Question 18

a unilateral lesion to the nerve or cochlear nuclei can cause what?

Answer 18

hearing loss - ipsilateral ear

*** does not cause deafness because there are bilateral projections at multiple sites in thee brainstem

Question 19

what types of sound information are transmitted to our brain?

Answer 19

tone- high and low frequency
amplitude of sound- loud or quite (differential firing of afferent fibers)
sound localization- superior olive nucleus, trapezoid body

Question 20

what fibers and nuclei allow us to regulate selective attention to certain sounds?

Answer 20

superior olivary nuclei and olivocochlear efferent fibers to inhibit outer hair cells

Question 21

what is conductive hearing loss?

Answer 21

occurs only in the outer and middle ear due to
- foreign bodies in the external auditory meatus
- perforated tympanic membrane
- otitis media
- otosclerosis ( overgrowth of bones around stapes)
- cholesteatoma (overgrowth of keratin debris within middle ear cavity)

Question 22

what is sensory neural hearing loss?

Answer 22

congenital hearing loss due to genetic mutations or developmental insults (acquired hearing loss)
- noisy induced hearing loss ( damage to stereociliated cells in organ of corti, loss of high frequency hearing first)
- aging related progressive bilateral/symmetric sensorineural hearing loss (hearing loss of higher frequencies due to destruction of hair cells at the cochlear base
- lesion in the auditory pathway

Question 23

what are the three auditory tests?

Answer 23

whisper, rinne and weber tests

Question 24

what is bone conduction (rinne)?

Answer 24

sound vibration can be transmitted through temporal bone vibration to inner ear

less effective than air conduction

Question 25

what is air conduction (rinne)?

Answer 25

sound transmission through tympanic membrane vibration and ossicle movement

more effective than bone conduction

Question 26

what are the findings for the rinne test?

Answer 26

with conductive hearing loss you can hear bone conduction more clearly than air conduction which is not normal

with sensory neural hearing loss you can hear air conduction more clearly than bone conduction

Question 27

what are the findings of the weber test?

Answer 27

with conductive hearing loss the affected ear will hear the tuning fork louder

with sensory neural hearing loss the sounds are heard better in the unaffected ear