lec 19 auditory system

Question 1

What are sounds?

Answer 1

• audible variations in pressure

- waves have freq/amplitude

Question 2

What is audible range of sound for humans?

Answer 2

freq ~20 Hz - 20,000 Hz

intensity 1-120 dB

Question 3

What are the 3 parts of ear?

Answer 3

outer = pinna + external auditory meatus

middle = ossicles, tensor tympani, stapedius, eustachian tube

inner = cochlea, canals, vestibule

Question 4

What is the function of the pinna?

Answer 4

• vertical localization of sounds

Question 5

What is the function of external auditory meatus?

Answer 5

• magnifies sound by passive resonance

Question 6

What are the ossicles?

Answer 6

3 bones of middle ear

• malleus [hammer] - associated with tympanic membrane
• incus [anvil]
• stapes [stirrup] - sits on oval window

Question 7

What two muscles in the middle ear? function?

Answer 7

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

Question 8

What separates outer from middle ear?

Answer 8

tymapnic membrane

Question 9

What innervates the tensor tympani?

Answer 9

motor root of trigeminal

“three Ts go together. tensor tympani trigeminal}

Question 10

What is the acoustic reflex?

Answer 10

stapedius shortens chain of ossicles thus dampening stapes movement, protects impact of loud sounds on inner ear

Question 11

What is function of eustachian tube?

Answer 11

provides air-air conduit between nasal passage and middle ear

• open during yawning, chewing, swallowing to equilibrate air pressure in middle ear with external

Question 12

What is difference between perilymph and endolymph?

Answer 12

perilymph = in bony cochlear, high K low Na, more aqueous
endolymph = in membranous cochlear, high K low Na, more viscous

Question 13

How many turns to cochlea?

Answer 13

2 3/4

Question 14

What connects the vestibule to the subarachnoid space?

Answer 14

perilymphatic duct for perilymph drainage

Question 15

What are the 3 compartments in the bony cochlea?

Answer 15

• scala vestibuli = in
• scala tympani = out
• scala media = membrane middle endolymph

Question 16

What are the 3 turns of the cochlea?

Answer 16

• basal, middle, apical

Question 17

What is the helicotrema?

Answer 17

apex of the cochlea

- where ripple wave loops back around and goes out

Question 18

Where are receptors for hearing located in cochlea?

Answer 18

the receptors are hair cells within organ of corti that rests on basilar membrane of scala media [on the tympanic side]

Question 19

What are the names of the two membranes surrounding scala media?

Answer 19

vestibular membrane on side of scala vestibuli

basilar membrane on side of scala tympani

Question 20

What is difference inner and outer hair cells?

Answer 20

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]

Question 21

How does hair bundle activate? inactivate?

Answer 21

activate = depolarization when bundle of sterocilia tilt toward kinocilium

inactivate = hyperpolarization when bundle of stereocilia tilt away from kinocilium

Question 22

How is sound produced in inner ear?

Answer 22

• 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 –>

Question 23

What is the difference between basilar membrane at base and apex?

Answer 23

apex: wider, more flexible, lower tones
base: narrower, stiffer, higher tones

Question 24

What is the function of outer hair cells?

Answer 24

• amplify movement of basilar membrane in response to low intensity sound
• make sound when they change height = otoacoustic amissions

Question 25

What part of ear is vulnerable to aminoglycoside antibiotics?

Answer 25

outer hair cells

Question 26

Where are cell bodies of auditory nerve fibers located?

Answer 26

spiral ganglion = within the bone of the spiral lamina of choclea

Question 27

What is path of bipolar auditory neurons from the spiral ganglion to the auditory cortex?

Answer 27

• 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

Question 28

If patient has unilateral hearing deficit where must the problem be along the auditory path?

Answer 28

must be in cochlear nucleus or auditory nerve or in the ear itself because everything else if bilateral

Question 29

What is the lateral lemniscus?

Answer 29

the fiber bundle output of the superior olive and cochlear nuclei

Question 30

What is the auditory nucleus in the thalamus?

Answer 30

medial geniculate nucleus [MGN]

Question 31

What structure is responsible for sound localization in the horizontal plane?

Answer 31

superior olive [due to its bilateral input]

-measures interaural intensity and timing difference to localize horizontally

Question 32

What is the olivocochlear bundle?

Answer 32

projects from superior olive to outer hair cells

• important pathway for selective auditory attention, control of noise masking, and protection from loud noise

Question 33

Where is the medial geniculate nucleus in the thalamus?

Answer 33

hangs off the bottom back of the thalamus

Question 34

What is the primary auditory cortex?

Answer 34

heschl’s gyri on superior temporal gyri

Question 35

How is the primary auditory cortex organized?

Answer 35

tonotopically

• low frequency in anterior
• high frequency in posterior

isofrequency bands = laterally oriented strips of cells that hare same characteristic frequencies

Question 36

What is function of wernicke’s area? location with respect to primary auditory cortex?

Answer 36

higher order auditory cortex area
important for speech recognition and comprehension

• caudal to primary auditory cortex on language dominant hemisphere