09 16 2014 Auditory system

Question 1

Volley theory

Answer 1

group of neurons of auditory system respond to sound by firing action potentials slightly out of phase so that when combined = greater frequency of sound can be encoded and sent to the brain to be analyzed

Question 2

Phase locking theory

Answer 2

matching amplitude times to a certain phase of another waveform

-firing an action potential at a certain phase of a stimulus sound being delivered

Question 3

Tinnitus

Answer 3

ringing of ears – can be pops, clicks, or rush

• common cause is inner ear damage
• symptom of menerie’s disease
• can also be caused by ototoxins

Question 4

ototoxins

Answer 4

agents that can damage both auditory and vestibular functions

-aminoglycoside antibiotics (streptomycin, gentamycin) and salcylates.

Question 5

otosclerosis

Answer 5

footplate of the stapes gets locked in place as a result of bone growth around the annular ligament– goes around stapes.

Annular ligament connects the stapes to the base of the oval window
- bone formation here prevents vibrations

Question 6

How is pitch perceived?

Answer 6

Place coding in different regions of the cochlear – selectively responsive to different frequencies of sound

-basilar membrane

Question 7

what happens to your ability to perceive pitch when there are very loud sounds around u?

Answer 7

• there is an overlap of frequencies = poor pitch discrimination

Question 8

Characteristic frequency

Answer 8

each auditory afferent displaces a CF –> the frequency at which the fiber has the lowest threshold to fire – aka when it will fire vs another fiber

Question 9

Innervation of cochlea?

Answer 9

Cochlea is composed of inner (1 row) and outer (3 rows) hair cells

90% bipolar cells of the spiral ganglion innervate the hair cells.

10% of spiral ganglion cells innervate the outer cells. Outer cells are also innervated (directly) by efferent fibers!

Question 10

time differences are monitored by what nucleus?

Answer 10

Medial Superior Olivary nucleus

• sound coming from right arrives at the right ear before the left ear.
• Axons vary in length to try to compensate for sound differences.

Question 11

intensity differences are monitored by what nucleus?

Answer 11

Lateral Superior Olivary Nucleus

-sound coming from right will be more intense on right

Question 12

how does one localize where sound comes from?

Answer 12

MSO and the detection of a binaural time difference. Sound hits one ear before the other.

Question 13

Meniere’s Disease

Answer 13

cc: vertigo, progressive hearing loss and tinnitus and feeling of a full ear
- overproduction of endolymp

Question 14

function of inner hair cells?

Function of outer hair cells?

Answer 14

–detection of sound

• participate in amplifying and dampening of sound stimulus (via motor force)
• motor: contract and elongate in synchrony with sound-evoked receptor potentials (motor protein –> prestin)

Question 15

Innervation of outer hair cells

Answer 15

contralateral innervation
Medial olivocochlear bundle
direct synaptic contacts

Question 16

Innervation of inner hair cells

Answer 16

mostly ipsilateral innvervation
Lateral olivocochlear bundle
axo-axonic contacts with bipolar cells

Question 17

Rinne Test

Answer 17

air conduction is compared to bone conduction

• hit runner, hold near ear (ask them until they stop hearing the sound) then put it on mastoid process and then asking them to tell you when vibration stopped
• conductive hearing loss: bone conduction is greater than air conduction

Question 18

Weber test

Answer 18

Tuning fork is placed on the vertex of skull in the midline. Patient is asked to where the tone sounds louder.

• normal: middle
• to one side: air conduction louder on affecter side OR louder on side that can hear (bone conduction defect)