Auditory

Question 1

What does each section of the ear do?

Answer 1

Outer captures sound
Middle ear amplifies and impedance matches
Inner ear transduces and encodes

Question 2

What are 2 types of hearing loss associated with damage to the middle ear?

Answer 2

Otitis media: middle ear infection often due to eustachian tube restriction
Otosclerosis: tissue overgrowth restricting ossicle (stapes) movement

Question 3

In the middle ear what do ossicles do?

Answer 3

Ossicles act as levers to
transform air borne vibrations
into fluid borne vibrations.

Question 4

Where are the frequencies on the basilar membrane?

Answer 4

high frequency at base

low frequency at apex

Question 5

The organ of corti has 2 groups of receptors. What are they?

Answer 5

Organ of court is the 3 laps of cochlea itself
Inner hair cells (single row) receive 95% of all afferents
Outer hair cells (3 rows) receive few afferents, but all 
 efferents

Question 6

What are steriocilia?

Answer 6

Hair cells are mechanoreceptors that are spacially tuned
Stereocilia: gated channels that open/close as stereocilia displace
Hair cells are frequency selective (have low threshold to specific frequency)
Hair cells are easily damaged (loud noices…)
stereo cilia arranged smallest to tallest
stereo cilia are cosine tuned. no matter what direction, as long as not straight up and down, some response is being activated

Question 7

Frequency tuning uses what 2 mechanisms?

Answer 7

Basilar membrane vibration

Resonant frequency of 
hair cell (membrane
 channels)

Question 8

Outer hair cells function to amplify/protect the cochlea. How?

Answer 8

Mechanical response of hair cell to
Membrane voltage change 
 Increase sensitivity of inner hair cells
 Sharpen tuning
 Regulated by efferents
 Produces otoacoustic emissions

Question 9

Auditory afferents are frequency tuned (low threshold at specific frequency). How?

Answer 9

Place code: array of CFs along tonotopic map

Rate code: firing rate proportional to sound 
 frequency

Question 10

How do cochlear implants work?

Answer 10

Implanted through mastoid into scala tympani
Only covers basal 40 – 50% of cochlea
Generally destroys basilar membrane, how then does it work?
Hint: stimulating contacts pointing toward the spiral ganglion cells


Question 11

Auditory first processes where, then what. Describe

Answer 11

Sound Localization (where it is) 
	
   Based on comparisons between ears
	
   Differences in timing, intensity 

Sound Identification (what it is)
	
   Emphasizes species-specific vocalizations


Question 12

What is Brainstem auditory evoked response (BAER)?

Answer 12

Clinical neurophysiology diagnostic
Evoked potentials elicited by repetitive clicks
Peaks at regular latencies are correlated with structures of auditory pathway
Shifts in latency or changes in amplitude indicate lesion


Question 13

Describe cochlear nuclei

Answer 13

CN is tonotopically organized
Bushy cells (ventral or ACN) project bilaterally to SOC: sound localization
Multipolar cells project only to contralateral IC: sound intensity
Octopus cells project to contralateral IC: speech frequency
Pyramidal cells project monaurally to contralateral IC; ?


Question 14

Describe the auditory cortex

Answer 14

Location: mainly in Sylvian fissure & superior temporal gyrus
Tonotopy arranged in isofrequency columns
Area 22 includes speech processing, damage results in Wernicke’s aphasia
Areas 44 & 45 (Broca’s aphasia) processes expressive speech and language


Wernicke’s area includes speech comprehension processing
Broca’s area processes expressive (production) speech and language


Question 15

What does the eustachian tube do?

Answer 15

Eustachian tube equilizes pressure between middle ear environment and outside. Without it the tympanic membrane could rupture

Question 16

What do the malleus, incus, and stapes do?

Answer 16

Malleus, Incus, Stapes act as a lever and this increases the amount of displacement by the air

Question 17

How does sound localization work?

Answer 17

Based on comparisons between ears

Differences in timing (ITD) used for frequencies below 1 KHz
Differences in intensity (ILD) used for frequencies above 3 KHz
Between 1 – 3 KHz, both ITD and ILD are used

Question 18

How does ITD work?

Answer 18

Based on specific anatomy of fibers projecting from both ears onto single MSO neurons.
Creates delay lines, MSO neuron only responds (spikes) when action potentials from both ears arrive simultaneously.
Some coincidence detectors only fire if sound stimulates both ears at the same time. other coincidence detectors only fire if sound stimulates the right ear first…

Question 19

Describe the Medial superior olivary complex processing

Answer 19

Sound localization

Frequency columns in MSO lie 
dorso-ventrally
Delay times along rostro-caudal axis
 of MSO

When interaural delay matches action potential arrival delay, cell reaches maximal firing. Coincident with location map.

Question 20

Describe the Inferior colliculus auditory space field

Answer 20

each neuron maximally responds to a sound coming from a specific direction and therefore can encode different place fields in auditory space.
These place fields are related to a head-centered reference frame, not space fixed.

Question 21

Describe the Superior colliculus deep layers

Answer 21

SC for auditory/visual integration of place fields

Visual centered stimulus produces peak of activity in rostral SC

Auditory stimulus to the left produces broader peak in caudal tectum. Broad due to larger receptive fields.

Combined visual and auditory stimulus produces single peak of activity located between unimodal stimulus peaks but biased toward visual. More salient visual cue

Question 22

Superior and inferior integration of modality cues

Answer 22

Superior colliculus has retinotopic map
Inferior colliculus has tonotopic map
Overlapping maps provide synchrony (common excitation to related stimuli)