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BAB > Audition > Flashcards

Audition Flashcards

1
Q

What 3 bones form the ossicles?

A

Malleus, Incus and Stapes

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2
Q

What is the function of the ossicles?

A

Link the tympanic membrane to the inner ear. They amplify the small membrane movement at the large oval window.

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3
Q

How is the middle ear linked to the nasal canal?

A

Via the eustachian tube

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4
Q

Why is the eustachian tube important?

A

It allows air pressure to equalise on either side of the tympanic membrane. Prevents a pressure build up from causing the membrane to bulge and inflicting pain. Fixed by swallowing.
Allows secretions of the middle ear to drain.

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5
Q

What does accumulation of middle ear secretions result in? Who is most at risk?

A

Middle ear infection.

Children have a short tube so reflux from nasopharynx to ear is common.

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6
Q

What is the attenuation reflex of the middle ear?

A

An involuntary response to reduce the volume of a stimulus on exposure to high intensities of sound. It reduces transmission of vibrating energy to protect the structures.

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7
Q

How is the attenuation reflex brought about?

A

Tensor tympani and stapedius muscles of the ossicles contract to reduce the movement of the ossicles by:

  • pulling the stapes away from the oval window
  • pulling malleus inwards to the middle ear
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8
Q

What structure forms the inner ear?

A

Cochlea - a spiral of three tubes

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9
Q

How does the middle ear communicate with the inner ear?

A

Tympanic membrane communicates to the cochlea at the apex where the helicotrema allows scala vestibuli to communicate with scala tympani.

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10
Q

What are the 3 tubes of the cochlea?

A

Scala vestibuli
Scala media
Scala tympani

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11
Q

What is the structure of scala media?

A

Fully enclosed tube that contains organ of corti. The primary sensory cells are surrounded by a tectorial membrane and fluid is produced by stria vascularis.

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12
Q

What is the structure of the scala tympani?

A

Lies below the basilar membrane. The membrane vibrates with fluid movement

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13
Q

How does the basilar membrane vary along its length?

A

Isn’t equally rigid.
Wide and floppy at apex - moves with low frequencies
Narrow and stiff at base - moves with high frequencies

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14
Q

What is the movement of the basilar membrane dependent on?

A

Frequency - determines which part moves

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15
Q

What induces movement of the basilar membrane?

A

Stapes footplate moves into the oval window to cause the round window membrane to move out and allow fluid movement within the cochlea, which will move the inner hair cells.

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16
Q

What is the organ of corti?

A

Situated on the basilar membrane. It contains rows of cilia that protrude from its surface to touch the tectorial membrane.

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17
Q

What sequence causes movement of the organ of corti?

A

Fluid movement causes the basilar membrane to move with different frequencies, the organ moves and the tectorial membrane slides over the hairs. The cilia excites the organ cells.

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18
Q

How many types of hair cells are there in the organ of corti?

A

Two: inner and outer.

Each hair cell has its own characteristic frequency.

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19
Q

How do the cilia excite the organ of corti?

A

The sterocilia are linked together by the caps of the mechanically gated K channels. As the cilia move together the channel will open or close.
Move away from each other = open channel
Move close together = close channel
Movement of K into the membrane causes depolarisation and this opens the Ca channels to trigger NT release into the synaptic cleft to excite the neuron.

20
Q

What do the neurons of the organ of corti form?

A

The spiral ganglion cells collectively form the auditory N

21
Q

What is the function of the outer hair cells? What type of signal do they produce?

A

MODULATE integration and control of signals. Many outer cells to 1 ganglion = CONVERGENT

22
Q

What is the function of the inner hair cells? What type of signal do they produce?

A

Pick up sound and turn it into an electrical signal for conscious sensory input. 1 cell to many ganglion cells = DIVERGENT

23
Q

How is a signal amplified?

A

Amplification is modulated by OUTER hair cells. Motor proteins within the cell contract or expand.
Contraction tougs the tectorial membrane and move the cilia. This is important for low intensities.

24
Q

What is the intensity of the frequency determined by?

A

Number of cells firing + Firing rate

25
Q

What is the frequency dependent on?

A

Each inner hair cell has its own characteristic frequency dependent on its basilar membrane location. The area of the membrane moves with different frequencies.

26
Q

What is tonotopy?

A

The SPATIAL ARRANGEMENT of the neurons in the auditory N travelling and synapsing in the cochlea nucleus is dependent on the FREQUENCY it detects. The location allows discrimination of the different frequencies.
Posterior = High frequency
Anterior = Low frequency

27
Q

What is phase locking?

A

Helps to discriminate and identify frequencies. The AP produced by the hair cell will fall on the same phase of the sound wave each time.
Each different frequency will lock at a different time in the wave.

28
Q

Why can high frequencies not use phase locking?

A

The sound wave firing is rate limited so it cannot lock at the same phase each time. Now reliant on tonotopy to determine the frequency.

29
Q

What is used to determine the frequency when it is

a) Very low
b) Intermediate
c) High?

A

a) Phase locking - less AP but still locks to same phase
b) Phase locking and tonotopy
c) Tonotopy

30
Q

In which N do the neurons run in to reach the cochlea nucleus?

A

Ipsilateral and contralateral auditory N

31
Q

What is different about the information being received via the contralateral auditory N? How does this help with localisation?

A

It has an interaural delay as the path is longer and it has an extra synapse.
The ipsilateral side will hit first so helps to determine where the sound is coming from.
The side perceiving more frequency = side of location

32
Q

Where does the contralateral cochlear N decussate?

A

At the superior olive creating the extra length and synapse

33
Q

Where is the auditory cortex located?

A

Temporal lobe with specific tonotopy.

34
Q

Where does the auditory pathway project from and terminate?

A
  • Organ of corti to auditory cortex via the auditory N
  • Auditory cortex to medial geniculate nucleus and inferior colliculus to send feedback to these areas
  • Inferior colliculus to pass to the medial geniculate nucleus and superior colliculus
  • Brainstem neurons to outer hair cell for regulating amplification
35
Q

What is the function of cortical connections from the auditory cortex?

A

Allows higher cognitive capacity to interpret written and spoken language

36
Q

What is conduction deafness?

A

Defective or limited CONDUCTION due to

  • Obstruction of auditory canal
  • Ostosclerosis = sclerotic degeneration of joints in ossicles
  • Ruptured ear drum/tympanic membrane = no ossicle movement
  • Middle ear infection
  • Head trauma
37
Q

What is nerve deafness?

A

Damage to INNER ear or ASCENDING pathways

38
Q

What are the genetic causes of nerve deafness?

A

> 40 genes linked
Recessive, dominant, X-linked mutations in structure or metabolism in the inner ear.
Can present as late onset hearing loss

39
Q

What are the congenital causes of nerve deafness?

A

Congenital rubella syndrome
CMV
Toxoplasmosis of newborn
Hypoplastic auditory N or abnormalities or cochlea

40
Q

What is Presbycusis, a cause of nerve deafness?

A

Progressive age related hearing loss of acuity or sensitivity.
Not preventable or reversible

41
Q

What may cause acquired nerve deafness?

A

Excessive noise causing acoustic trauma/cochlear damage. Temporary or permanent.

42
Q

What acquired diseases may cause nerve deafness?

A 
Inflammatory
Meningitis
DM
Stroke
Viral - AIDS, measles, mumps, herpes
Tumour
Trauma
Hypothyroidism / iodine
43
Q

What are the iatrogenic causes of nerve deafness?

A
  • Aminoglycerides: Antibiotic that causes an extent of deafness in all Pts but with varying severity and recovery. A mitochondrial mutation can increase risk of more severe effect.
  • Methotrexate: Treats AI hearing loss by reducing inflammation but can cause loss itself as a side effect if prolonged high dose. Irreversible.
44
Q

What are the perinatal causes of nerve deafness?

A

Premature
Fetal alcohol syndrome
Syphilis syndrome

45
Q

What does dysfunction of the outer hair cells cause?

A

Continuous contraction that amplifies noise causing perception of things that aren’t there = TINNITUS (noisy ear)

BAB (11 decks)

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