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ENT Patrick Stenhouse > Physiology - Hearing and Balance > Flashcards

Physiology - Hearing and Balance Flashcards

1
Q

When using an audiogram to assess normal hearing what does the 0dB line represent?

A

Softest sound that a person with normal hearing ability would be able to detect at least 50% of the time

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2
Q

What is the range for normal hearing?

A

-10 to 20dB

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3
Q

What is the range for classifying:

a) Mild hearing loss
b) Moderate hearing loss
c) Severe hearing loss
d) Profound hearing loss

A

a) 20 - 40dB
b) 40 - 70dB
c) 70 - 100dB
d) >100dB

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4
Q

What is the ratio of the tympanic membrane surface area to the oval window, and why is this the case?

A

18:1

More pressure must be concentrated in a smaller area as the oval window oscillates against the perilymph fluid which requires more force (versus air) to move

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5
Q

How can the Eustachian tube be opened?

A
  1. Tensor veli palatini muscle
  2. Levator palatine muscle
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6
Q

What is the purpose of opening the Eustachian tube?

A

Equalises pressure between the middle ear and external environment

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7
Q

Dysfunction in the Eustachian tube may lead to what?

A

Middle ear negative pressure

(and many conditions such as glue ear may follow)

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8
Q

What are the two openings in the cochlea which can be accessed via the middle ear?

A
  1. Oval window
  2. Round window
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9
Q

Which three chambers can be found within the cochlea?

A
  1. Vestibular duct (scala vestibuli)
  2. Tympanic duct (scala tympani)
  3. Cochlear duct (scala media)
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10
Q

Name the chambers A, B and C within the cochlear cross section

A

A - Scala vestibuli

B - Scala media

C - Scala tympani

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11
Q

Which chamber within the cochlea borders the oval window?

A

Vestibular duct (scala vestibuli)

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12
Q

Which chamber within the cochlea borders the round window?

A

Tympanic duct (scala tympani)

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13
Q

Which type of fluid do the following chambers contain?

a) Vestibular chamber (scala vestibuli)
b) Tympanic chamber (scala tympani)
c) Cochlear duct (scala media)

A

a) Perilymph - Vestibular chamber (scala vestibuli)
b) Perilymph - Tympanic chamber (scala tympani)
c) Endolymph - Cochlear duct (scala media)

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14
Q

What is special about the endolymph which can be found in the cochlear duct (scala media)?

A

It has a very high potassium concentration

Hair cells project into the cochlear duct

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15
Q

How does the perilymph differ from the endolymph in terms of its biochemical components?

A

Perilymph - High Na+ Low K+

Endolymph - High K+ Low Na+

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16
Q

Which organ lies on the basilar membrane of the ear?

A

Organ of Corti

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17
Q

What is the modiolus?

A

Conical shaped central axis in the cochlea

Consists of spongy bone

(cochlea turns approximately 2.5 times around it)

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18
Q

In the ear, what does the term transduction refer to?

A

Conversion of mechanical (bending of hair cells) energy to electrical impulse

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19
Q

How are the stereocilia arranged?

A

In height order

20
Q

What is the significance of the stereocilia being arranged in height order?

A

Depolarisation will occur when stereocilia become deflected towards the longest

Hyperpolarisation will occur when the sterocilia become deflected away from the longest

21
Q

After depolarisation of the Organ of Corti occurs, what happens next?

A
  1. CN VIII stimulated
  2. Central pathways carry impulse
  3. Activity occurs in superior temporal gyrus where the primary auditory cortex is found
22
Q

What is Oscillopsia?

A

A condition causing the whole visual field to oscillate making focussing and balance very difficult

Nausea and vomiting is common

It is often due to the vestibulo-ocular reflex being lost

23
Q

Which central pathways contribute to a sense of balance?

A
  1. Visual - eyes stay balanced
  2. Proprioceptive - hips knees and back
  3. Vestibulospinal tract - central pathways
  4. Cardiovascular - perfused by a good cardiovascular system
  5. Vestibular - tone to muscles
  6. Vestibulo-ocular reflex - can focus on a distant object whe you are moving
24
Q

What is the overall structure of the inner ear called?

A

Labyrinth

25
Q

What are the otolith organs in the ear?

A

Saccule and utricle

26
Q

What are the 5 vestibular end organs in the inner ear?

A

Otolith organs (saccule and utricle)

Ampullae of lateral, posterior and superior semicircular canals

27
Q

What is the otoconia?

A

Small crystals of calcium carbonate found in the saccule and utricle

When impacted in a certain direction, they stimulate the hair cells by their movement relative to the gelatinous supporting substrate (contains hair cells)

28
Q

Which organs have stereocilia pointing into the gelatinous matric with otoconia?

A

Saccule and utricle

29
Q

What causes movement to be detected?

A

Otoconia move with gravity

This impacts on the gelatinous matrix which in turn bends the stereocilia (act like tree branches in heavy snow)

This causes depolarisation or hyperpolarisation when the head is tilted in a certain direction

30
Q

When will firing from the otolith organs stop?

A

Linear motion

(it always continues with a head tilt, but stops in the neutral position)

31
Q

How are the otolith organs orientated?

A

They have a 360° orientation ensuring all planes of motion can be detected

32
Q

Which types of hair cells can be found in otolith organs?

A

Type 1 (true receptors)

Type 2 (amplifiers)

33
Q

The semicircular canals are orientated at ___ degrees to each other

A

The semicircular canals are orientated at 90° degrees to each other

34
Q

What are the structures found in the ampullae of the semicircular canals?

A

Cupulae

35
Q

What causes deflection of a cupula and what is the impact of this?

A

Movement of endolymph

Bending of cupula then causes stereocilia to deflect

(N.b. The cupula will deflect in the opposite direction to the direction of movement due to inertia)

36
Q

What is nystagmus?

A

Involuntary eye movements can occur from side to side, up and down, or in a circular pattern

It can be a clinical sign for vertigo and is a failure of the vestibulo-ocular reflex

37
Q

How may pathology of the vestibular system manifest?

A

Vertigo

38
Q

Which drug may induce oscillopsia when used periorbitally?

A

Gentamicin

39
Q

Where does the vestibular nuclei output to?

A
  1. Vestibulospinal tract (motor output to neck back and leg muscles) - posture
  2. Medial longitudinal fasiculus and ocular muscles (motor output to eyes)
  3. Medial lemniscus and thalamus to cerebrum - awareness
40
Q

Why are the hairs in the cochlea so special?

A

Particular hairs respond to particular frequencies of sound

  • high frequency is at the base whereas low frequency is at the end of the spiral meme
41
Q

Where is the scala media(endolymph) suspended between?

A

scala tympani and scala vestibuli (perilymph)

42
Q

What is the fucntional unit of the organ or orti?

A

inner hair cell

43
Q

What do oval and round windows do?

A

Permit transmission of pressure wave in an enclosed canal and vibration of basilar membrane

44
Q

What is the eustachian tube?

A

Ventilation pathway for middle ear - resting state is closed but opneed by tensor velo palatini and levator palatine muscles

it acts to equalise ears

45
Q

when can babies hear shit in the womb?

A

18 weeks a foetus can hear

26 weeks it will respond to sounds

46
Q

What does kinocilium mean?

A

the longest one of the hairs

ENT Patrick Stenhouse (27 decks)

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