auditory system structure and function of middle ear

Question 1

outer ear

Answer 1

pinna (auricle) skin coverve cartilaginous structure, channels sound waves into ear canal

ear canal from concha to ear drum, the outer third is cartilaginous the inner is bony, boosts in high frequency sound intensity

Question 2

middle ear

Answer 2

mechanical system
ossicular chain that extends from the tympanic membrane to oval window of the inner ear
As sound pressure waves move the malleus the incus and the stapes

to overcome impedance mismatch (from air to fluid), the sound is amplified by a lever mechanism and the area difference between the tympanic membrane and oval window, which increases the force per unit area

to protect the ear theres a tensor tympani (inn trigemincal) and the stapedius (inn facial nerve)

Question 3

inner ear

Answer 3

mediates 2 functions: hearing and balance

contained in the petrous apex of the temporal bone encased in the osseous or bony labyrtinth

labyrinth consists of 3 continuous sections the vestibule, the chochlea and the semicircular canals

Question 4

cochlea anatomy

Answer 4

the core of the cochlea is the modiolus, porous bone that allows the passage of the auditory nerve, the osseous spiral lamina juts out of the modiolus

in the spiral lamina is 3 compartments, the upper and lower are the scala vesibuli and the scala tympani (contain perilymph low in K and high in Na)

in the middle is the scala media ( the upper boundry is the reisseners membrane and the basilar membrane on the bottom) (contains endo lymph with a high concentration of K and lowNA) with the organ of corti and the lateral edge is stria vascularis ionic concentrations maintained by stria vascularis

Question 5

organ of corti

Answer 5

one row of inner hair cells and three rows of outer hair cells

hair cells are contacted by the dendrites of afferent bipolar cells whose cell bodies are in the spiral ganglion

efferents through the superior olivary complex

Question 6

inner and outer hair cells

Answer 6

inner hair cells (innervated by 90-95 % of the cochlear afferents)

outer hair cells (innervated by 5% of the the cochlear afferents)

motile properties of sterocilia and basilar membrane motion are responsible for the cochlear amplifier

Question 7

mechanics of the cochlea

Answer 7

at the base the basilar membrane is narrow and stiff (where high frequencies are detected) and the apex is wide and floppy (low frequency is detected) “tonotopic organization”

stapes moves the fluid which causes a traveling wave

produces deflection of the stereocilia, opens ion channels, depolarize cells, NT release stimulates the auditory nerve

Question 8

hearing loss

Answer 8

genetics, meds, infection, trauma cause hearing loss

Conductive hearing loss: occlusion or disfunction of the external/middle ear

sensorineural hearing loss: dysfunction of the cochlea or auditory nerve