Inner Ear

Question 1

Bekesy travelling wave theory is

Answer 1

It demonstrates that a travelling wave of motion swept along the basilar membrane - where it reaches a maximum displacement of amplitude and then the vibration dies out rapidly. The position of maximum amplitude varies with the frequency of signal. Low frequencies reach peak at apex and high frequencies reach peak at base

Question 2

3 main functions of cochlea: transmission

Answer 2

The sound is transfers from the oval window to the organ of corti.

Question 3

3 functions of cochlea: transduction

Answer 3

Is converting the mechanical energy(vibrations) into electro-chemical energy. Inner hair cells are sensory transducers, they convert motion of stereocillia into neurotransmitter release. Outer hair cells have both forward and reverse transduction.

Question 4

3 main functions of cochlea; frequency resolution

Answer 4

Is breaking sound up into its component frequencies. this is known as Bekesy travelling wave, where the response begins at the base. As it travels apically amplitude grows. It reaches its peak at the point determined by frequency of sound then vibration dies out rapidly.

Question 5

What is temporal resolution

Answer 5

Helps to determine what frequency has been heard/stimulated by the cochlea. If a frequency of 1kHz is presented to the ear - a pattern of nerve impulses that repeats 1000 times per second will travel to the brain.

Question 6

What are the electrical potentials of the cochlea?

Answer 6

In resting state(no sound)
Endolymph +80mV
Hair cell -40 to -70 Mac
Perilymph 0mV

Question 7

What is summating potential?

Answer 7

It is the inability for the stria vascularis to maintain the +80mV in endolymph when subject to long and intense signals. No charge means brain does not hear the signal.

Question 8

Role of the OHC: amplification

Answer 8

Sounds less than 50dBSPL will not create a big enough wave to sheer the IHC- the outer hair cells can still be stimulated. They send an afferent signal to the brain which leads to the tectorial membrane pulling down making the IHC sheer, creating impulses as normal

Question 9

Role of OHC: limiter

Answer 9

Loud signals are detected by the outer hair cells- efferent impulses are received from the brain which forces the OHCs to elongate and push the tectorial membrane up which limits response from IHCs

Question 10

Role of OHC: fine tuning

Answer 10

The electromotility of the OHCs acts on the basilar membrane causes wave to focus on a smaller group of hair cells. This aids frequency resolution (sharper hearing) and temporal resolution (gaps in sound)

Question 11

Anatomy of cochlea

Answer 11

Conical: snail shaped
36mm long, 10mm x 5mm diameter
Spirals 2.75 around modiolus
Osseous spiral lamina
Membranous lining

Question 12

What are the three tubes within the cochlea?

Answer 12

Scalia vestibuli: contains perilymph
Scala Media: contains endolymph
Scala Tympani: contains perilymph

Floor between Vestibuli and Media is Reissners membrane and between tympani and media is basilar membrane.

Question 13

Describe Scala media/cochlea duct?

Answer 13

It is a membranous tube that runs along the outer wall of the cochlea. Floor basilar membrane and roof is reissners membrane. Stria vacularis are cells that sit above it and pump it with potassium. Forms a triangular duct.

Question 14

Inner hair cells

Answer 14

-3500 per cochlea
-single row
- pear shaped
-50/60 stereocillia per cell
- Afferent: ear to brain
- sensory
-involved with SN loss

Question 15

Outer hair cells

Answer 15

• 12500 per cochlea
• 3 rows
• test tube shaped
• 100 stereocillia in V or W shaped
• efferent brain to ear
  -impact sensitivity of cochlea
• motor (mechanical)