9 Auditory and Vestibular Organs

Question 1

I only made cards for the points that he said were potentially on the test. If you want to learn the rest of the material, look thru the packet.

Answer 1

Remember what our tutors said :)

Question 2

What are the 2 methods of impedance matching in the ear?

Answer 2

• Lever: Malleus handle (manubrium) is 3x longer than incus process.
• The tympanic membrane is 18x bigger than the oval window (area of 55 versus 3)

Question 3

Base of the basilar membrane receives high or low sound? What is its characteristics?

Answer 3

• High frequencies

- Narrow and stiff (as opposed to wide and flexible at apex)

Question 4

Cochlear amplification occurs about how far along the cochlea? How much dB in amplification? What is it due to?

Answer 4

• About halfway to the apex.
• 50dB
• Electromotility of outer hair cells (via Prestin protein localized in outer hair cell membrane. Loss of this=hereditary hearing loss)

Question 5

Describe the afferent innervation of the hair cells?

Answer 5

• Inner hair cells: Type 1 spiral ganglion neurons. About 20 nerves/hair cell, each nerve only synapses on 1 hair cell.
• Out hair cells: Type 2 spiral ganglion neurons. Each neuron synapses on 6-100 hair cells (generally in the same row).
• See pic

Question 6

Describe the efferent innervation of the hair cells?

Answer 6

• Inner hair cells: Efferent (axoaxonic) innervation of type 1 spiral ganglion neurons
• Outer hair cells: Efferent innervation of outer hair cells

Question 7

Describe the vestibular ocular circuitry coming from the LEFT lateral SCC when I turn my head to the left?

Answer 7

Cristae ampullaris of left lateral SCC sends rapid action potentials, so…

• -Travels thru Vestibular Ganglion and excites Left Medial and Superior Vestibular nuclei
• ——–Excites Left medial rectus via CN 3
• ——–Excites Right lateral recuts via CN 6

Question 8

Describe the vestibular ocular circuitry coming from the RIGHT lateral SCC when I turn my head to the left?

Answer 8

Cristae ampullaris of right lateral SCC slows down its action potentials, so…

• -Travels thru Vestibular Ganglion and inhibits Right Medial and Superior Vestibular nuclei
• ——–Inhibits Left lateral rectus via CN 6
• ——–Inhibits Right medial rectus via CN 3

Question 9

What does a tip link do?

Answer 9

• Open the hair cell transduction channels

- These are mutated in Usher syndrome=deaf & blind

Question 10

What are tip links composed of?

Answer 10

• Cadherin 23

- Protocadherin 15

Question 11

Where is K+ concentration high? (endo or perilymph?)

Answer 11

Endolymph in the scala media