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ENT Medicine > Physiology of Hearing and Balance > Flashcards

Physiology of Hearing and Balance Flashcards

1
Q

What is sound?

A

A pressure wave caused by oscillating molecules (set in motion by vibrations)

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2
Q

What does frequency dictate?

A

Pitch

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3
Q

What does amplitude dictate?

A

Intensity

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4
Q

What range can human detect sounds in?

A

20-20000 Hz

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5
Q

How does the external ear act as a receiver for sound?

A

Shaped to receive airborne sounds (huge variation in shape)

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6
Q

What does the ossicular chain of the middle ear acts?

A

Piston/lever arm = varying efficiency depending on frequency of sound transmitted

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7
Q

What is the tympanic to OW ratio in the middle ear?

A

18:1 (impedance matching air to liquid) = leads to pressure gain of 22x

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8
Q

What is the ratio of the malleus handle to the incus long process in the middle ear?

A

1.3:1 = gain of 20-25dB (theoretical gain in 34dB)

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9
Q

What is the Eustachian tube?

A

Ventilation pathway for middle ear mucosa = has bony and cartilaginous portions

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10
Q

What is the resting state of the cartilaginous tube of the Eustachian tube?

A

Closed = opened by tensor veli palatini and levator palatine muscles

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11
Q

What does dysfunction of the cartilaginous tube in the Eustachian tube cause?

A

Middle ear negative pressure

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12
Q

What are the oval and round windows of the ear?

A

Two openings of the cochlea to the middle ear = have in-phase movement

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13
Q

What do the oval and the round windows of the ear allow?

A

Transmission of pressure wave in enclosed canal and vibration of the basilar membrane

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14
Q

Where is the pressure wave transmitted to from the oval and round windows of the ear?

A

Perilymph

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15
Q

How is the inner ear structured?

A

Curved spiral lamina = two and a half turns around central modiolus (need to consider ultrastructure of cochlea)

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16
Q

Where is the scala media (endolymph) of the cochlea located?

A

Suspended between scala tympani and scala vestibuli (perilymph)

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17
Q

What is within the cochlea of the ear?

A

Coiled tube of liquid = actively maintained in specific concentration to power cells

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18
Q

How does sound stimulate the 8th cranial nerve and then the central pathways?

A

Wave passes through cochlea, maximally stimulating a particular area of the basilar membrane, then the organ of Corti here depolarises and fires to stimulate nerve

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19
Q

Where does sound activity culminate?

A

In the superior temporal gyrus

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20
Q

What is the input and output displayed by the modified Romburg’s test for balance?

A 
Input = vestibular
Output = vestibulospinal
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21
Q

What is the structure of the inner ear like?

A

Complex structure termed the labyrinth = bony and membranous structures

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22
Q

What are the five key vestibular end organs present in the inner ear?

A 
SVN = lateral/anterior superior semi-circular canal, utricle
IVN = posterior semi-circular canal, saccule
23
Q

What are the hair cells of the inner ear?

A

Kinocilium and stereocilia = resting potential is 90 spikes/s, deflection towards increases

24
Q

What are the otolith organs of the ear?

A

Utricle and saccule

25
Q

What is present in the maculae of the otolith organs?

A

Stereocilia = project upwards into a gelatinous matrix with otoconia

26
Q

How are the stereocilia of the otolith organs orientated?

A

In all directions = all movements perceived by changes in resting firing rate

27
Q

How does the brain interact with the otolith organs?

A

Perceives position and movement when tilting head/linear motion (lend weight and due to gravity)

28
Q

How are the semi-circular canals of the inner ear orientated?

A

At 90 degrees to each other so paired, equal and opposite

29
Q

What sits within the ampulla of the semi-circular canals of the inner ear?

A

Cupula

30
Q

What does bending of the semi-circular canals of the inner ear cause?

A

Causes stereocilia to deflect

31
Q

What causes the semi-circular canals of the inner ear to deflect?

A

Movement of perilymph

32
Q

What does VOR stand for?

A

Vestibulo-ocular reflex

33
Q

What feeds into the cupula of the inner ear?

A

The christa ampullaris

34
Q

What occurs in the vestibulo-ocular reflex?

A

Movement of head to left causes inhibition

Movement of head to right causes excitation

35
Q

When may nystagmus occur during the vestibulo-ocular reflex?

A

When turning towards a particular side (ie on left side when turning left), on left side when there is neuritis

36
Q

What is the input and output to the vestibulo-ocular reflex?

A 
Input = vestibular
Output = vestiblo=ocular
37
Q

What is oscillopsia?

A

Objects appear to move or tremble when they are still = occurs when there is no vestibular input

38
Q

What is nystagmus?

A

Rhythmic abnormal eye movements

39
Q

What is the vestibulo-oculo reflex?

A

Activation of vestibular system of inner ear

40
Q

What does the modified Romburg’s test assess?

A

Tests for presence of two out of three = neurological function for balance, assesses proprioception, vison and vestibular function

41
Q

What is the central pathway for balance?

A

Complex series of communications in vestibul nuclei

42
Q

Where do vestibul nuclei have output to?

A

Vestibulospinal, medial longitudinal fasciculus and ocular muscles, medial lemniscus and thalamus

43
Q

Where does the vestibulospinal tract have outputs to?

A

Motor output to neck, back and leg muscles

44
Q

Where do the medial longitudinal fasciculus and ocular muscles have output to?

A

Motor output to eyes

45
Q

Where do the medial lemniscus and thalamus send outputs to?

A

The cerebrum

46
Q

What is the function of the hair cells in the ear in terms of sound?

A

Transduction = conversion of mechanical bending force into electrical impulse

47
Q

How are stereocilia of the ear arranged?

A

In height order with tip links connecting them together

48
Q

When does hyperpolarisation and depolarisation of the ear hair cells occur?

A

Depolarisation occurs when deflected towards longest

Hyperpolarisation occurs when deflected away

49
Q

Where is the primary auditory complex of the brain?

A

Left posterior temporal gyrus = Brodman areas 41/42

50
Q

When does firing of the cilia in the otolith organs stops?

A

Stops with linear motion so you know movement has stopped (but continues with head tilt)

51
Q

How are the otolith organs orientated?

A

360 degree orientation so all planes of motion detected

52
Q

What type of hair cells are present in otolith organs?

A

Type 1 and 2

53
Q

What increase and decreases the resting potential of the otolith organs?

A

Direction of bend towards or away from the kinocilium

ENT Medicine (22 decks)

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