Auditory

Question 1

What is the Auditory System?

Answer 1

Determines the frequency, intensity and other properties of sounds
Interprets meaning of sound
Identifies source of sounds - sound localization

Question 2

What is sound?

Answer 2

Audible variations in air pressure

- mechanical energy measured as the calculated pressure that a wave makes against an object (ear drum).

Question 3

Sound Waves

Answer 3

Produced by vibrations of air molecules

Question 4

Tonotopy

Answer 4

Mapping of sound frequencies on basilar membrane - Principle of adequate stimulus

Question 5

Frequency Coding at Basilar membrane

Answer 5

Hair cells along basilar membrane have receptive fields differing in frequency preference

Question 6

Frequency Coding or Tonotopy

Answer 6

Neural encoding of pitch (place codes)

Question 7

Base of Basilar Membrane

Answer 7

Short and Stiff Fibers

Question 8

Apex of Basilar Membrane

Answer 8

Long Floppy Fibers

Question 9

Resonance

Answer 9

The tendency of a system to oscillate at a greater amplitude at some frequencies than at others.

Question 10

Resonant Frequency

Answer 10

Small periodic driving forces can produce large amplitude oscillations because the system stores vibrational energy

Question 11

High Frequency

Answer 11

Waves vibrate stiff fibers best (at base): travel short distance

Question 12

Low Frequency

Answer 12

Waves vibrate floppy fibers best (at apex): travel entire distance

Question 13

TRPA Channel

Answer 13

A family of transient receptor potential ion channels

• TRP channel blocks K+ ions and others @ tip links
• Stretch-activated channel opens when mechanically stimulated

Question 14

Perilymph

Answer 14

In the Scala Vestibuli and Scala Tympani

Low K+, High Na+

Question 15

Endolymph

Answer 15

In Scala Media

High K+, Low Na+

Question 16

Endocochlear Potential

Answer 16

Endolymph is 80 mV more positive than perilymph

Question 17

Rapid Responsiveness ( Temporal Fidelity)

Answer 17

TRPA1 channels respond to stretch with 10 us speed, faithfully traduced high frequency signals

Question 18

TRPA1 Channel Sensitivity and Range

Answer 18

High Sensitivity

Range: soft to loud sounds (displaces stereocilia from 0.3 nm to 20nm)

Question 19

Biphasic Receptor Potential

Answer 19

Mimics sound waves - contains bi-polarity that resembles the peak and trough of a sound wave

Question 20

Inner Hair Cells

Answer 20

Type of Spiral Ganglion cell
95% of SGC receive auditory information from inner HCs
High Fidelity
Myelinated Fibers

Question 21

Outer Hair Cells

Answer 21

Type of Spiral Ganglion Cell
5% of SGC receive auditory info from outer hair cells
Many HCs feed to one SGC - low fidelity
Unmyelinated Fibers

Question 22

Primary Auditory Area

Answer 22

Brodmann’s Area 41

Question 23

Secondary Auditory Area

Answer 23

Brodmann’s Area 42

Question 24

Isofrequency Bands

Answer 24

Cortical columns with different tonal receptive fields

Question 25

Frequency Coding in CNS

Answer 25

Basilar Membrane (PNS)-> Spiral Ganglion -> Auditory Nerve -> Cochlear Nucleus (CNS)

Question 26

Binaural Auditory Neurons

Answer 26

Found at Superior Olive and above. | Each cochlea is bilaterally represented in the brain.

Question 27

Receptive Fields of Central Auditory pathway

Answer 27

Complexity of stimuli detected increases as you ascend the pathway : Cochlear nucleus and MGN

Question 28

Further processing

Answer 28

Inferior Colliculus sends signals to superior Colliculus (integration of auditory and visual info) and cerebellum

Question 29

Extensive Feedback from Central Auditory pathway

Answer 29

- Descending Efferents from Brainstem (to superior olive) contact and modulate OHCs in cochlea - Efferent storm auditory cortex send axons to MGN and inferior Colliculus

Question 30

Ventral Cochlear Nucleus

Answer 30

Receives auditory signals ipsilaterally | - if severed, you will e deaf on the same side

Question 31

What are the 3 mechanisms of Intensity Coding?

Answer 31

1. Stronger Displacement - increase firing rate to affected sensory n. (Temporal summation) 2. Wider area displaced - more auditory sensory n. activated (spatial summation) 3. Special Hair Cells that have a High Threshold - only intense sound will make the AP Fire.

Question 32

Place Code

Answer 32

Displacement of Basilar Membrane = a function of pitch (frequency) and intensity - can interfere with Tonotopy because louder sounds can have a different frequency

Question 33

Phase Locking

Answer 33

Consistent firing of a cell at the same phase of a sound wave - alt method for frequency coding - works well at low frequencies (20 - 200Hz)

Question 34

Phase Locking with Volley

Answer 34

@500Hz - 4kHz frequencies are represented by pooled activity of several auditory n, each member firing in a phase locked manner - shared wave among population of neurons

Question 35

Very Low Frequency sound coding mechanism

Answer 35

20 - 200 Hz | Phase Locking

Question 36

Intermediate Frequency Sounds coding mechanism

Answer 36

Phase Locking (200Hz - 500Hz [limit for phase locking]) Phase Locking with Volley (500Hz - 4kHz) Tonotopy

Question 37

High Frequency sound coding Mechanism

Answer 37

Tonotopy (>4kHz - 20 kHz)

Question 38

Duplex Theory of Localization

Answer 38

Two Different Processes: Interaural Time Delay and Interaural Intensity Difference

Question 39

Interaural Time Delay (ITD)

Answer 39

Sudden sounds of all frequencies and continuous sounds of 20 - 2000Hz

Question 40

Interaural Intensity Difference

Answer 40

Continuous Sounds with high frequencies (2 - 20kHz)

Question 41

Sound Shadow

Answer 41

Head casts a sounds shadow to the ear further from the sound, Lower intensity sound at one ear is a cue that the origin of sound is in the other direction