Hearing

Question 1

What does the cochlea detect and how?

Answer 1

Wavelength - pitch
Amplitude - loudness
Wave form - tone/timbre (resonance)

Question 2

What is the function of the ossicles?

Answer 2

Match the impedance of the air to the impedance of the fluid within the inner ear
- making sound waves passing through the air matched to sound waves passing through fluid

Question 3

Describe the basilar membrane

Answer 3

Wider at the apex, stiffer at the base

- base responds to high frequencies, apex responds to low frequencies

Question 4

How does the signalling work with the hair cells in the cochlea?

Answer 4

Deflection of hair bundle towards the kinocilium causes opening of potassium channels –> increased K+ and depolarisation, opening of VDCC and release of glutamate

Question 5

What is the importance of potassium in the cochlea?

Answer 5

Potassium serves to both depolarise and repolarise the cell

- it is recycled through potassium channels in the scala media

Question 6

What do inner hair cells do?

Answer 6

Transduce sound information

- 95% of the nerves that project to the brainstem nuclei

Question 7

What do outer hair cells do?

Answer 7

Efferent inputs from the superior olivary complex

• more outer hair cells than inner hair cells
• change length –> this accentuates movement of the basilar membrane –> amplifies the signal that is received by the IHCs
• without OHCs, basilar membrane movement is 100 fold less

Question 8

What is the auditory pathway?

Answer 8

• From the hair cells in the cochlea –> CNVIII go to the IPSILATERAL cochlear nuclei in the medulla –> spiral ganglion –> superior olive –> lateral lemniscus –> inferior colliculus
• • extensive crossing over of information from the cochlear nuclei to the superior olive

Question 9

What are the different parts of the superior olivary complex?

Answer 9

MSO: localisation of sound by measuring time delay
LSO: localisation of sound by sensing intensity differences

Question 10

What is the Duplex theory (for low frequency)?

Answer 10

Sound localisation in the horizontal plane
- the time that sound arrives at each ear –> have a difference in when the signals get to that neuron (one path is longer than the other) –> time difference is sent up the pathway to tell the brain that one ear is hearing it before the other

Question 11

What is the Duplex theory (for high frequencies)?

Answer 11

Head acts as a wall, therefore sound is louder in one ear

- involves some inhibitory nuclei in the trapezoid body

Question 12

How is the auditory cortex arranged?

Answer 12

Neurons are sharply tuned for sound frequency with columnar organisation
- alternating regions of input from both ears