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Neuroanatomy > Auditory + Vestibular System > Flashcards

Auditory + Vestibular System Flashcards

1
Q

Components of external ear

A

Auricle

EAM

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2
Q

What separates the outer ear from middle ear?

A

TM

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3
Q

What are the three main chambers of the middle ear?

A

Tympanic cavity

Mastoid antrum

Eustachian tube

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4
Q

What are the three ossciles and what do they abut

A

TM-> malleus-> incus-> stapes-> oval window (ossicle)

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5
Q

Contents of the middle ear

A

Nerves:

Facial nerve

Chorda tympani

Lesser petrosal nerve

Tympanic branch of the glossopharyngeal nerve (Jacobsen’s nerve)

A branch from internal carotid plexus

Ossicles

Tensor tmpani muscle

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6
Q

Roof of middle ear

A

Tegmen tympani

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7
Q

Posterior wall of middle ear

A

Mastoid

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8
Q

Anterior wall of middle ear

A

Carotid wall

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9
Q

Lateral wall of middle ear

A

Membranous (tympanic)

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10
Q

Floor of middle ear

A

Jugular wall

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11
Q

Superior relation of middle ear

A

Tegmen tympani separates it from the middle cranial fossa

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12
Q

Inferior relation of middle ear

A

Jugular bulb, there can be congenital dehiscnece of floor with jugular bulb in middle ear placing it at risk of injury

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13
Q

Medial relation of middle ear

A

Labyrinth and lateral semiciruclar canal lies posterosuperior to facial nerve

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14
Q

Posterior relation of middle ear

A

Sigmoid venous sinus

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15
Q

Anterior relation of middle ear

A

Petrous part of ICA in carotid canal

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16
Q

Posterior relation of middle ear

A

Posteromedial to mastoid air cells- cerebellum in posterior cranial fossa

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17
Q

Compartments of the middle ear

A

Epitympanic recess/attic

Tympanic cavity

Hypotympanum-> Eustachian tube opening

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18
Q
A
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19
Q

Components of inner ear

A

Bony labyrinth- formed by openings in petrous portion of temporal bone

Membranous labyrinth- formed by simple epithelial membrane

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20
Q

Relation between membranous and bony labyrinth

A

Membranous labyrinth lines the contours of the bony labyrinth and is filled with endolymph

The bony and membranous labyrinths are separated by perilymph

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21
Q

What are the components of the membranous labyrinth

A

Cochlea (auditory labyrinth)

Utricle, saccule and semicircular canals (vestibular labyrinth)

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22
Q

Components of the cochlea

A

Bony core- mediolus which contains cochlear part of CN VIII

Cochelar canal which winds two and a half times around the mediolus

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23
Q

Divisions of the cavity of the cochlear canal

A

Scala vestibuli- above

Scala media- middle

Scala tympani- below

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24
Q

Endolymph is found in which scala?

A

Scala media

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25
Q

Perilymph is found in which scala

A

Scala vestibuli and scala tympani

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26
Q

How are the scala vestibuli and scala tympani in communication

A

At the apex of the cochlea called the helicotrema

The scala media ends in a blind-ended sac

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27
Q

What separates the scala vestibuli from scala Media?

A

Reisnner’s membrane

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28
Q

What separates the scala media from the scala tympani

A

The basilar membrane

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29
Q

How are Reisner’s and basilar membranes attached to the bony wall of the cochlear canal?

A

Spiral ligament

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30
Q

What is the organ of Corti?

A

Composed of sensory hair cells on the scala media side of the basilar membrane

Contains stereocilia that project into the overlying gelatinous structure- tectorial membrane

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31
Q

Describe how audotiry signals are transduced

A

Inward movement of the oval window by stapes sets up a fluid wave along scala vestibuli and scala tympani across the scala media to cause upward displacement of the basilar membrane

The basilar membrane is forced up against the fixed tectorial membrane with shearing forces exerted on stereocilia causing excitation of sensory hair cells.

Point of maximum displacement is determined by sound frequency displacement- low frequency= maximum near the base, high frequency- maximum near the apex.

The excitability of cochlear hair cells is frequency-dependent.

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32
Q

What happens after fluid waves have crossed the scala tympani

A

Cause the round window membrane to move in and out

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33
Q

Which two features of the middle ear enhance the efficacy of energy transfer from air to fluid

A

The oval window is substantially smaller than tympanic membrane- vibratory force is greatly magnified at the fluid interface of the oval window

Use of TM and ossicles reduces energy loss from higher acoustic impedance of transition from air to fluid

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34
Q

Brainstem organisation of afferent auditory fibres

A

Cochlear nerve fibres terminate on both dorsal and ventral cochlear nuclei which maintain tonogrpahic organisation of cochlea

Dorsal cochlear nuclear fibres project axons across midline in dorsal acoustic striae-> lateral lemnicsuc-> inferior colliculus

Ventral cochlear nuclear fibres-> ipsilateral and contralateral superior olivary nucleus via trapezoid body. Then ascend in contralateral lateral lemniscus-> inferior colliculus

Inferior colliclus-> MGN via inferior brachium

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35
Q

Function of superior olivary nucleus w.r.t auditory tract

A

Concerned with sound localisation

Compares differences in the timing of sounds received and intensity

Projects to the nucleus of lateral lemniscus and the inferior colliculus

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36
Q

What is the only part of the ascending auditory pathway that does not have commissural connections?

A

MGN

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37
Q

How do the lateral lemnisci communicate?

A

Via commissure of Probst

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38
Q

Electrical stimulation of the primary auditory cortex

A

Produces sensation of simple sounds such as buzzing or ringing

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39
Q

Electrical stimulation of the auditory association areas

A

Complex sounds e.g. dog barking or familiar voice

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40
Q

Organisation of auditory cortex

A

Tonotopicaklly

Low frequency sounds anteriorly

High frequency posteirorly

Summation columns associated with binaural input and suppression columns monaural input

41
Q

Clinical features of conducitve hearing loss

A

Reduction in hearing

Maintain good ability to hear loud noises

Hear better in setting of noisy backgrounds

42
Q

Clinical features of sensorineural hearing loss

A

Selective difficulty hearing high pitched sounds and vowels

Loss of speech discrimination out of proportion to pure tone deafness

Difficulty hearing speech that is mixed with background noise

43
Q

Low pitch tinnitus frequently associated with

A

Conductive hearing loss

44
Q

High frequency tinnitus assocaited with

A

Sensorinueral hearing loss

45
Q

In which condition is sensorineural hearing loss associated with low frequency tinnitus?

A

Meniere’s

46
Q

Subjective tinnitus

A

Only experienced by patient

47
Q

Objective tinnitus

A

Experienced by patient and examiner

48
Q

Causes of objective tinnitus

A

Eustachian tube dysfunction

Ossicles

Palate

Cerebral vascular malformations or aneurysms

49
Q

Weber’s lateralises to right

AC>BC on right

A

R SNHL

50
Q

Weber’s lateralises to right

BC>AC on right

A

R Conductive hearing loss

51
Q

Cochlear lesion causing high frequecny hearing loss

A

Base of cochlea (due to tonotopic arrangement)

52
Q

Cochlear lesion causing low frequency hearing loss

A

Apex of cochlea

53
Q

Unilateral auditory cortex lesion

A

Results in difficulty localising signs

May make it difficult for a listener to ignore background noise or competing measures

54
Q

Draw the ascending auditory pathway

A
55
Q

Disequilibrium

A

Represents malfunction of one of the three communicating systems- visual, proprioceptive, vestibular

56
Q

Basic function of vestibular system

A

Coordination of motor control

Posture

Equiibrium

Eye movements

57
Q

What structures constitute the vestibular portion of the labyrinth

A

Utricle

Saccule

Semicircular canal

58
Q

Function of utricle and saccule

A

Detect linear acceleration and the position of the head in space

59
Q

Structure of utricle and saccule

A

Dilatation of membranous labyrinth, surrounded by perilymph

Filled with endolymph and lined by simple cuboidal epithilium except at receptor rich areas called maculae

60
Q

Components of the utricle and saccular maculae

A

Supporting cells- columnar epithelial cells continuous with the simple cuboidal epithelial cells that line the utricle and saccule

Hair cells which are specialised receptors cells intercalated between the supporting cells

Otolithic membrane (gelatinous mass embedded with calcium carbonate otoliths) that covers hair cells

Dendrites of cells in the vestibular ganglion

61
Q

Arrangement of macular hair cells

A

Hair of maculae are microvilli each containing 40-80 with a single kinocilium that arises from a centriole.

One kinocilium is located in the periphery of each hair cell, thus polarising the hair cell

62
Q

Polarisation of utricular and saccular maculae

A

Kinocilia of the maculae are arranged to polarise the maculae in relation to an imaginary curved line called the striola

Utricular maculae are polarised towards the striola

Saccular maculae are polarised away from the striola

63
Q

Functional significance of the otolithic membrane

A

Exerts gravitational pull on hair cells.

The orientation of the hair cells relative to this gravitational force determines the direction of their displacement

Displacement of hair cells along the axis of polarisation depolarises the cells and initiates excitatory impulses

Displacement of hair cells in the direction opposite hyperpolarises the cells and initiates an inhibitory impulse

64
Q

Plane of saccule

A

Vertical

65
Q

Plane of utricle

A

Horizontal

66
Q

The function of semicircular ducts

A

Provide information bout the angular acceleration fo the head in any direction but do not detect its ability in a static position

67
Q

Functional significance of the semicircular canal

A

Each duct enlarges at point of attachment to the utricle- ampullae which are the functional counterparts of the maculae

Contained thickened sensory epithelium called ampullary crest which contains kinocilia containing hair cells

These hair cells are embedded in a gelatinous mass- the cupula and fill space between crest and roof of the ampulla

Angular acceleration of the head causes displacement of endolymphatic fluid and movement of cupula causing stimulation of hair cells.

68
Q

Cupula vs otolithic membrane

A

Cupula lacks calcium carbonate crystals

69
Q

Central projections of vestibular system

A

Spinal cord

Cerebellum

Nuclei controlling EOMs

70
Q

Scarpa’s ganglion

A

Vestibular ganglion which lies at the base of the IAC

71
Q

Through which cerebellar peduncle to vestibular fibres pass

A

Inferior cerebellar peduncle

72
Q

Longitudinal vestibular spinal tracts

A

Vestibulospinal tract

MLF

Direct fibres

73
Q

Medial vestibulospinal tract

A

Originates in medial vestibular nucleus, projects corssed and uncrossed fibres in the desecending MLF as far as the cervical spinal segements

74
Q

Lateral vesteibulospinal tract

A

Arises in lateral vestibular nucleus (Deiter’s nucleus)
Projects uncrossed fibres to all levels of the SC

75
Q

Deiter’s nucleus

A

Lateral vestibular nucleus

Sends fibres to lateral vesitbulospinal tract

76
Q

Where do vestibulospinal tract fibres terminate

A

Rexed Laminae VII and VIII which facilitate extensor muscles

Provide physiological basis for maintenance of extensor muscle tone required for upright posture

77
Q

Direction of nystagmus

A

Named for fast phase

It is actually the direction of slow phase that is pathological with the fast phase representing corrective compensatory eye movements

78
Q

Visual fixation and nystagmus

A

Visual fixation inhibits peripheral vestibular nystagmus

79
Q

Differentatiating factors between peripheral and central nystagmus

A

Central- multidirectional without inhibition by fixation

80
Q

Destructive peripheral nystagmus

Fast phase to right

A

Unopposed tonic firing of right labyrinth-> slow gaze to left with corrective movements to the right (fast phase to right)

Left-sided pathology

81
Q

Signs and symptoms of peripheral vestibular pathology

A

Pathology affecting vestibular labyrinth or ganglia

May present with hearing loss, tinnitus, aural fullness, and or pain

Facial weakness and hearing loss if a ganglial lesion

Past-pointing on the affected side

Rotatory nystagmus inhibited by visual fixation

Associated autonomic symptoms may be seen

82
Q

Central vestibular lesions

A

CPA lesions:

Hearing loss and tinnitus

Loss of corneal reflex

Facial weakness

Ipsilateral ataxia and intention tremor

Brainstem and cerebellar

Mild vertigo

Other CN palsies- diploploia, dysarthria, perioral numbness

Long tract signs

Hearing loss and tinnitus absent

83
Q

Location of peripheral vestibular lesions

A

Labyrinth

Ganglia

84
Q

Vestibular labyrinth lesions

A

Episodic vertigo

Hearing loss, tinnitus, aural fullness

Otalgia

On examination patient points towards the affected side

On examination, patient points to the affected side

Spontaneous nystagmus with fast phase away from the affected side, rotatory and inhibited by fixation

Prounced symptoms with nausea and vomiting

85
Q

Lesions in vestibular ganglia and nerve at IAC

A

May have facial weakness due to close proximity to facial nerve

Hearing and tinnitus often present but vertigo less prominent and aural fullness/otalgia absent

86
Q

Central vestibular lesions location

A

CPA and brainstem

87
Q

CPA lesions

A

Progressive hearing loss and tinnitus

Loss of ipsilateral corneal reflex and facial numbness

Facial weakness

Ipsilateral ataxia and intention tremor

Contralateral hemiparesis and hemisensory loss

Vertigo, nystagmus and autonomic symptoms mild

88
Q

Brainstem and cerebeullm vestibular lesions

A

Isolated vestibular lesions are rarely the result of lesions in brainstem or cerebellum

Vertigo associated with diploplia, dysarthria, perioral numbness

Long tract signs

Hearing loss and tinnitus typically absent

89
Q

Localisation of gaze evoked nystagmus

A

Non-localising

90
Q

Downbeat nystagmus

DC

A

Cervicomedullary junction

(posterior fossa)

91
Q

Upbeat nystgamus

UV

A

Vermis

92
Q

Localising nystagmus

A

Should be in primary position, not gaze evoked

93
Q

Convergence retraction

CD

A

Dorsal midbrain

94
Q

Seesaw nystagmus
ST

A

Third ventricular/parasellar region

95
Q

Brun’s nystagmus

BC

A

CPA

96
Q

Difference between rebound and periodic alternating nystagmus

A

PAN alternates side to side with periodicity

Rebound is gaze-evoked

97
Q

What is the location of the cochlear?

A

B

98
Q
A

Neuroanatomy (18 decks)

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