Hearing Flashcards

1
Q

What is sound?

A

It is a compressive wave which travels at 343m/sec in air

It has 2 properties:
Frequency (Hertz(Hz))
Volume (Decibels(dB))

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the human auditory range?

How does it change with age?

A

20Hz to 20000Hz

With age, normal loss of the upper range of frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe the cochlea.

A

It is a one dimensional (linear) sense-organ

It consists of 3 layers:
Scala vestibule
The basilar membrane
Scala tympani

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How does the organ of Corti sense sound?

A

It has hair cells that detect movements and convert it to signals
These cells are covered by a tectorial membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the travelling wave theory?

A

von Bekesy showed that the basilar membrane resonates and so mechanically amplifies sound with progressively lower frequencies along the length of the cochlea

So the lower the frequency the further along the cochlea it is sensed
So the place at which a sound is sensed is determinate on its frequency.
This is tonotopy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How are the hair cells within a cochlea arranged?

A

Inner hair cells - 1 row
Sense sound

Outer cells - 3 rows
Serve as amplifiers

They are mechanically tuned, by their position along the cochlear
And
Electrically tuned by expression of particular ion channels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How do the stereocilia on hair cells work to interpret sound.

A

The stereocilia are of differing heights and have potassium channels on them connected to each other by protein chains
If the stereocilia are displaced:
If pushed towards the smaller ‘hair’ then the protein chains become shorter and close the K+ channels
If pushed towards the larger ‘hair’ then the protein chains become longer and open the channels

Because the environment of the endolymph (ECF around hair cells) has a high conc. of K+ and the ICF is low in K+ so the influx of K+ depolarises the cell and causes neurotransmission to the spiral ganglion neurite.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Tell me about the spiral ganglion neurons.

A

45,000 SGN (afferent axons 8th nerve

SGN types:

  • Type 1 (95%) inner hair cell (IHC)
  • Type 2 (5%) outer hair cell (OHC)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What do the outer hair cells do?

A

They are supplied by efferent feedback from the olivocochlear bundle (OCB) within the olivocochlear system

They serve as cochlear amplifiers
They receive a signal and create a force by changing in length to help amplify the sound for the IHC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How is sound encoded to account for volume?

A

At a low level of sound not many action potentials fired, at higher levels more fired and at even higher levels, surrounding IHC fire action potentials as well

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Where does the signal travel from the cochlea?

A

Via CN VIII, to the cochlea nucleus
Which travels to the medial nucleus of the trapezoid body (MNTB) on the opposite side

Which then has links to the lateral and medial superior olives (LSO/MSO)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the auditory pathway?

A
Cochlea
Spiral ganglion nucleus
Cochlear nucleus
Superior olivary complex
Inferior colliculus
Medial geniculate nucleus
Auditory cortex
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What can cause hearing impairments?

A
Loud noise
Congenital defects (inherited)
Infections (e.g. rubella, glue ear)
Ototoxic comp. (aminoglycosides)
Trauma (damage to temporal bone)
Age
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How can you assess haring?

A

Visual inspection (otoscope)

Audiograms: plot sensitivity against frequency
- Provides an overall measure of hearing sensitivity

Otoacoustic emissions (OAE)
This is the sound generated by OHC
Tests for amplifier function

Auditory brainstem response (ABR)
Also used to general hearing function in babies

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the different sites of hearing loss?

A

Conductive hearing loss

  • Blockage, ruptured eardrum
  • Fluid accumulation (otitis media)
  • Otosclerosis (progressive oscicle immobilisation)

Sensory loss

  • Hair cell destruction (physical, noise related)
  • Hair cell death (ototoxic; e.g. kanamycin)

Neural hearing loss
- Spiral ganglion damage (e.g. acoustic neuroma)
- Age-related hearing loss (ARHL, possible links with
dementia)
- Tinnitus - Phantom sound (associated with hearing loss)
- Auditory neuropathy (with hyperbilirubinaemia,
neonatal jaundice)
- Monaural deafness - destroys ability to localise sound

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the treatments for hearing loss?

A

Hearing aides

Cochlea implants
Direct electrical stimulation of spiral ganglion

Cochlear nucleus implants
Direct stimulation of neurons in the first nucleus of the auditory pathway

Hair cell regeneration?
Yet to be achieved in mammals

17
Q

Tell me about congenital deafness.

A

More than 300 syndromes linked to deafness
1 in 1000 children are deaf by adulthood

Three broad groups
DFN - Inherited - X-linked
DFNA - Inherited - autosomal dominant
DFNB - Inherited - autosomal recessive