VIII-Hearing/Loss

Question 1

normal human hearing range

Answer 1

20 Hz - 20 kHz

Question 2

humans most sensitive to what frequency

Answer 2

1-4 kHz

Question 3

presbycusis

Answer 3

age related hearing impairment that begins with high freq hearing range

Question 4

function of outer ear

Answer 4

collect sound waves
-resonant frequency ~3.5 kHz

Question 5

function of middle ear

Answer 5

transmit sound energy in the air to fluid filled cochlea (impedance match)

Question 6

cochlear tonotopy

Answer 6

base of basilar membrane (in cochlea, closer to round window) tuned to high freq

apex (center of cochlea) tuned for low frequencies

Question 7

steps of mechanoelectrical transduction

Answer 7

traveling sound wave induces
1. vertical movement of basilar membrane = shearing/mechanical force
2. stereocilia deflecting toward tallest stereocilia
3. opens cation channels (mechanically gated K+ channels) to depolarize hair cell = inc Glu release
4. inc firing rate of CN VIII

Question 8

middle ear acoustic reflex

Answer 8

stapedius (CN VII) contracts in response to loud sounds
-changes ossicle position to dec transmission of vibrational energy to cochlea

tensor tympani from CN V also attenuates loud sounds

Question 9

hyperacusis

Answer 9

painful sensitivity to low-moderate intensity sounds from facial nerve/stapedius damage

seen in bell’s palsy

Question 10

central auditory pathways

Answer 10

1. ipsilateral cochlear nerve fibers end at cochlear nuclei CN VIII
2. projections from nuclei bilateral to brainstem areas
3. medial geniculate nucleus of thalamus
4. primary auditory cortex

Question 11

bilateral distribution in CNS

Answer 11

ascending order of bilateral projections:
1. superior olive @ mid pons
2. nucleus of lateral lemnicus @ pons/midbrain junction
3. inferior colliculus @ caudal midbrain

so if lesion unilateral no deafness in either ear

Question 12

causes of conductive deafness

Answer 12

impaired transmission in external or middle ear
-ear wax
-otosclerosis
-fibrosis from repeated infections
-otitis media with effusion (non infectious)
-tympanic membrane damage

Question 13

causes of sensorineural hearing loss

Answer 13

loss of hair cells
-aging
-ototoxic drugs like antibiotics
-excessive noise exposure
-tumors (vestiblar schwannoma, acoustic neuroma)

treat with cochlear implants

Question 14

causes of central hearing loss

Question 15

location of primary auditory cortex

Answer 15

aka A1 @ temporal lobe
adjacent to wernickes area for speech comprehension

Question 16

superior olive function

Answer 16

integrate sound info from both ears to compute location of a sound
-via interaural time difference or intensity difference