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Neuroanatomy > Hearing and balance > Flashcards

Hearing and balance Flashcards

1
Q

Describe what is sound?

A
  • sound waves are pressure waves with alternating peaks of compressed air and valleys
  • distinguished by amplitude (dB) and frequency (Hz)
  • converted to APs in cochlea
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2
Q

Describe the external auditory canal

A
  • S shaped (boosts 3kHz sounds-speech)
  • elastic cartilage portion runs posterosuperior
  • inner bony portion runs anteroinferior
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3
Q

What is the reason for the shape of the pinna?

A
  • differentiation of location of sounds

* on ground vs in tree

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4
Q

Describe the tympanic membrane

A
  • angled
  • connective tissue
  • skin externally
  • mucous membrane lined internally
  • attached by fibrocartilaginous ring to temporal bone
  • concavity at centre
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5
Q

Describe the middle ear

A
  • air-filled
  • mucous membrane lined
  • in the temporal bone
  • 2 parts: tympanic cavity and epitympanic recess
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6
Q

What is the roof of the middle ear?

A

tegmental (temporal bone) wall -middle cranial fossa

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7
Q

What is the floor of the middle ear?

A

jugular wall

• tympanic nerve from CNIX

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8
Q

What is the lateral wall of the middle ear?

A

membranous wall
• tympanic membrane
• temporal bone

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9
Q

What is the posterior wall of the middle ear?

A

mastoid wall

• chord tympani

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10
Q

What is the anterior wall of the middle ear?

A

carotid wall

• auditory tube

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11
Q

What is the medial wall of the middle ear?

A

labyrinthine wall

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12
Q

Describe the mastoid area

A
  • posterior to epitympanuc recess
  • mastoid antrum: cavity continuous with air filled spaces
  • separated from middle ear by thin tegmen tympani
  • mucous membrane continuous from middle ear to mastoid antrum (infection spreads)
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13
Q

Describe the pharyngotympanic tube

A
  • connects ME to nasopharynx
  • equalizes pressure
  • extends from anterior wall of ME, anteriorly, medially and inferiorly to nasopharynx posterior to inferior meatus
  • 2 parts: bony (lateral 1/3) and cartilaginous part
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14
Q

Describe the ossicles

A
  • synovial joints (subject to osteoarthritis with age)
  • from tympanic membrane to oval window
  • muscles contract to dampen prolonged noises
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15
Q

List the muscles of the middle ear?

A
  • tensor tympani

* stapedius

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16
Q

Tensor tympani

A

O: pharyngotympanic tube, sphenoid, bony canal
I: upper handle of malleus
N: mandibular branch CNV
F: reduce vibrations in loud noises

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17
Q

Stapedius

A

O: attached to inside of pyramidal eminence
I: neck of stapes
N: branch of facial nerve
F: prevents excess oscillation in loud noises

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18
Q

How well is the sound transferred in middle ear?

A
  • ossicles transmit to oval window

* >60% of sound energy is successfully transferred to cochlea

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19
Q

Describe the bony labyrinth

A
  • vestibule
  • semicircular canals
  • cochlea
  • lined with periosteum and contain perilymph
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20
Q

Describe the membranous labyrinth

A

Suspended in perilymph

Membranous structures filled with endolymph:
• semicircular ducts
• cochlear duct
• utricule and sacule

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21
Q

List the organs of balance

A
  • semicircular ducts
  • utricle
  • saccule
22
Q

Describe the cochlea

A
  • located centrally in bony labyrinth, dividing it into 2 canals: Scala vestibuli and Scala tympani
  • connected via lamina modiolis
  • spiral ligament
  • vestibular membrane
  • basilar membrane
  • spiral organ
23
Q

spiral ligament

A

thickened outer wall against bony cochlea

24
Q

vestibular membrane

A

separates endolymph in cochlear duct from perilymph in scala vestibuli

25
Q

basilar membrane

A

separates endolymph in cochlear duct form perilymph in scala tympani

26
Q

spiral organ

A
  • organ of hearing
  • rests on basilar membrane
  • projects into cochlear duct
27
Q

Describe the transmission of sound from oval window and on?

A

Oval window moves medially

  • > creates wave in perilymph of Scala vestibuli
  • > wave through cochlea causing and outwards bulging of secondary tympanic membrane at round window
  • > causes basilar membrane to vibrate
  • > receptor cells in spiral organ stimulated
  • > receptor cells transmit to brain through CN
28
Q

Modiolus

A

• core spongy bone and contains cavity (spiral ganglion) that contains nerve cell bodies of sensory afferents

29
Q

Where are the low frequency tones? and high?

A
  • low frequency are at apex

* high at base

30
Q

Describe the organ of corti

A
  • lies on basilar membrane within cochlear duct
  • made of sensory receptors: inner and outer hair cells
  • stereo cilia project up from hair cells and are embedded in tectorial membrane
  • bending of stereocilia
  • outer hair cells control sensitivity if inner hair cells: modulate basilar membrane movement and act as amplifiers
31
Q

Describe the auditory pathway

A

• first order neurons in CNVIII

  • > enter brainstem at pontomedullary junction
  • > synapse on dorsal and ventral cochlear nuclei
32
Q

Dorsal cochlear nucleus

A
  • 2nd order fibres cross midline and join lateral lemniscus, the major ascending auditory pathway -> synapse at inferior colliculus
  • 3rd order neurons -> synapse medial geniculate bodies in thalamus
  • 4th order neurons run to primary auditory cortex in superior temporal gyrus of temporal lobe
33
Q

Ventral cochlear nucleus

A
  • 2nd order fibres remain ipsilateral and cross midline -> run to superior olivary nuclei in pons (sound localisation)
  • 3rd order neurons join lateral lemniscus -> inferior colliculus -> thalamus -> cortex
34
Q

What is the consequence of unilateral damage above the cochlear nuclei?

A
  • does NOT cause deafness
  • problems with localizing sounds and separating sound from background noise
  • each lateral lemniscus contains info from both ears
35
Q

What is the result of damage to CNVIII?

A

deafness in that ear

36
Q

What is conductive hearing loss?

A
  • sound through outer or middle ear interrupted
  • wax, ruptured eardrum, otitis media, arthritis of ossicles
  • hearing aids boost sounds to counter reduced conduction
37
Q

What is sensorineural hearing loss?

A
  • cochlea (hair cells, auditory nerve or auditory cortex damaged
  • lost high frequencies: old age and loud noise
  • head injury, hereditary, stroke, drugs
  • cochlear implant works IF CNVIII is intact
38
Q

List the hearing loss screening tests

A
  • Weber

* Rinne

39
Q

What is the Weber test?

A
  • differentiate conductive from sensorineural loss
  • compares hearing in both ears (should be equal)
  • bang fork and press on bone -> compare one to the other
40
Q

What is the Rinne test?

A

• finds conductive loss ONLY
• bang the fork and hold on mastoid until patient can’t hear it anymore, then quickly place it in front of ear
-> if can hear it back again, then conductive loss

41
Q

What are the organs of balance?

A
  • utricle (largest sac)
  • 3 semicircular canals
  • saccule (smaller sac)
42
Q

What are the sensory receptors of balance?

A
  • macula of utricle: centrifugal and vertical acceleration
  • macula of saccule: linear acceleration
  • crista: movement in any direction
43
Q

What is the pathway for balance?

A

semicircular canals, saccule and utricule -> vestibular nuclei
a-> neocortex (perceived orientation)
b-> spinal cord & cerebellum (postural control)
c-> oculomotor system (eye movements
d-> parabrachial nuclei check congruency with visual, proprioceptive inputs (motion sickness if not congruent)

44
Q

What is the name of the spot that controls motion sickness?

A

area postrema

45
Q

Describe the semicircular ducts

A
  • crista in ampulla contain hair cells and supporting cells
  • crista is small elevation covered by cupula
  • cupula is mass of gelatinous material
46
Q

What happens in semicircular ducts during head movement?

A

semicircular ducts and hair cells move

  • > hair bundles bend
  • > receptor potential
  • > nerve impulses
  • > vestibular branch of CN
47
Q

Describe the utricle and saccule anatomy

A
  • macula has sensory hairs in gelatinous otolithic membrane containing otoconia or otoliths
  • otolithic membrane denser than endolymph (flops when head moves)
  • otoliths move downward with gravity, stimulating hair cells (tells us which way is up)
  • macula responds to force of gravity
  • saccule=vertical motion
  • utricule = horizontal motion
48
Q

What do the vestibular nuclei have connections with?

A
  • spinal cord extrapyramidal and vestibulospinal tracts
  • motor nuclei of CNIII, IV, and VI
  • cerebellum - vestibulocerebellar tracts
  • vestibular neocortex of insulating and parietal lobes via thalamus (consciousness of movement)
  • autonomic or visceral nuclei in reticular formation (maintaining BP)
49
Q

What is the vestibule-ocular reflex?

A
  • generates eye movements to compensate for head movement
  • fix gaze on object while head moves
  • to maintain balance and orientation
  • semicircular canals -> vestibular nuclei -> 2nd order neurons -> motor nuclei of CNIII, IV and VI via MLF
  • vestibulocerebellum adapts (inhibits) this reflex
50
Q

What is vertigo?

A 
Disturbance in vestibular pathway:
• physiological
• peripheral -inner ear disease (eg. BPPV)
• central (brainstem, cerebellum)
• altered sensory input

Neuroanatomy (9 decks)

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