Lecture 9: Auditory system

Question 1

Which organ decomposes sound intto separate frequencies?

Answer 1

Cochlea (slakkenhuis)

Question 2

What is a Fourier series

Answer 2

Sum of sines and cosines –> sound/waveform

Question 3

What are the sensory receptors of the auditory system?

Answer 3

Hair cells in the organ of Corti

Question 4

What is tonopy?

Answer 4

Spatial mapping of sounds frequencies in the auditory system.

Question 5

How is the tonopy mapped in the basilar membrane?

Answer 5

• Base –> high frequencies
• Apex –> low frequencies

Question 6

How does the cochlea create tonotopy?

Answer 6

The changing width and stiffness of the basilar membrane.

Question 7

Where does transduction in the cochlea happen?

Answer 7

In the organ of Corti where hair cells are located. They convert acoustic stimuli into electrochemical signals

Question 8

What is the difference between inner and outer hair cells?

Answer 8

• Inner hair cells can only transduce mechanical stimuli to electrochemcial, making them the real sensory transducers
• Outer hair cells can transduce from mechanical to electrochemical and the other way around

Question 9

What happends when a travelling wave hits the basilar membrane?

Answer 9

The basilar membrane will move. This will cause relative movement between basilar membrane and tectorial membrane, causing stereocilia to bend. Bending of the stereocilia triggers an electrical response in the hair cells

Question 10

What happens when there is deflection towards the shortest stereocilia and if towards the longest stereocilia?

Answer 10

Towards shortest stereocilia: hyperpolarization
Towards longest stereocilia:
depolarization

Question 11

What is the AC and DC component of a (stimulus) signal?

Answer 11

AC component is the part that fluctuates/changes over time

DC component is the part that stay steady/constant that remains unchanged over time

Question 12

Which claim about sensory transduction of hair cells is incorrect?

1. The AC component of hair cells is small at high stimulus frequencies
2. Deflection of the cilia towards the longest cilium produces depolarization
3. The electrical activity initiated by the tip links is transferred to the vesicular release sites
4. The firing frequency (number of actoin potentials) in hair cells depends on the frequency of the auditory stimulus

Answer 12

4

Question 13

What is the cochlear amplifier?

Answer 13

Sharp peak in the cochlea - increase sensitivity to low-intensity sounds + improved frequency resolution

Question 14

Which motor protein in the lateral membrane of outer hair cells cause mobility and what does it enhance?

Answer 14

Prestin, enhances vibration of basilar membrane

Question 15

How does the cochlear amplifier work in OHC?

Answer 15

It is a positive feedback mechanism:
Voltage dependent prestin contract, making the distance between the basilar membrane and the reticular lamina smaller. This amplifies the amplitude of the travelling wave across the basilar membrane, sharpening the sound.

Question 16

What type of ganglion cells synapse with hair cells and what do their axons form?

Answer 16

Spiral ganglion cells, axons form the VIII cranial nerve/auditory nerve
They are bipolar neurons

Question 17

What should be encoded in de auditory system?

Answer 17

Intensity, location, frequency = submodality

Question 18

What is the characteristic frequency?

Answer 18

Frequency with lowest input required

Question 19

Why can the cochlea and nerve be considered as a filter bank?

Answer 19

each inner hair cell + coupled nerve fibers analyzes narrow band of frequencies; the entire auditory nerve convers the entire audible frequency range

Question 20

How is intensity encoded?

Answer 20

Firing frequency & number of neurons
1. Number of APs per second, that increases with the intensity of the input.
2. The number of neurons firing, that increases with the intensity of the input

NOTE: increase intensity –> increases number of spikes

Question 21

How is frequency encoded?

Answer 21

Place (tonotopy)
Frequency (phase-locking)

Question 22

Which of the following sttements about the auditory nerve fibers is false?

1. Afferent fibers receive input from inner hair cells.
2. High frequency fibers can respond well to stimuli at frequencies in the rang of 10 to 20 kHz in humans.
3. The characteristics frequency of the hair cells systematicaly varies along the length of the cochlear axis.
4. One ganglion cell makes contact with one outer hair cell.

Answer 22

4

Question 23

What is the anatomy of the superior olivary complex?

Answer 23

• Medial nucleus of the trapezoid body (MNTB)
• Lateral superior olive (LSO)
• Medial superior olive (MSO)

Question 24

What is the function of the medial and lateral superior olive?

Answer 24

MSO: ITDs –> interaural time differences – MSO = for low frequencies
LSO: ILDs –> interaural level differences – LSO is for high frequencies

Question 25

Is there a time/phase difference between the ears when..

• Distance from the sound source for both ears is equal
• Source is closer to one ear than the other

Answer 25

• no
• yes

Question 26

What happens with the cells in the LSO when a speaker makes a sound at the left ear?

Answer 26

Cells in the LSO receive an excitatory activation from the left ear (ipsilateral ear).
Cells in the LSO receive an inhibitory activation from the right ear (contralateral)
It gives difference in sound intensity for the particular frequency

NOTE: LSO transmits result to contralateral hemisphere

Question 27

What is the pathway from the superior olivary nucleus to the auditory cortex?

Answer 27

Cochlear nucleus (medulla) –> superior olivary nucleus –> medial geniculate nucleus (thalamus) –> auditory cortex

Question 28

What is the first brain structure in the auditory system that receives information from both left and right ear?

Answer 28

Superior olive