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CNS > Ear & Vestibular System > Flashcards

Ear & Vestibular System Flashcards

1
Q

What are the three parts of the ear?

A

External Ear, Middle Ear, Inner Ear

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2
Q

Where are the parts of the ear located?

A

Petrous part of the temporal bone

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3
Q

What does the inner ear consist of?

A

Bony labrinth

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4
Q

What is within the bony labrinth?

A
  1. All cavities of bony labrinth filled with perilymph (clear extra-cellular fluid containing high Na+ and low K+)
  2. ENcasing within the bony labyrinth is the membranous labynth (containing endolymph)
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5
Q

What are two main functional parts of the inner ear?

A
  1. Cochlea - hearing: impulses passed to the brain via the auditory nerve
  2. Vestibular System - balance and posture: impulses passed to brain via vestibular nerve
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6
Q

What two places does the middle ear connect to?

A
  1. Eustachian Tube
  2. Mastoid Air Sinuses (mastoid part of the temporal bone)
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7
Q

What is the importance of the eustachian tube?

A

Re-equilibriate pressure of middle ear to pharynx

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8
Q

What is the importance of the eustachian tube?

A

Re-equilibriate pressure of middle ear to pharynx

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9
Q

What are the 3 chambers of the cochlea?

A
  1. Scala Vestibuli (upper part of cochlea)
  2. Scala Tympani (lower part of cochlea)
  3. Scala Media. (Cochlea Duct)
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10
Q

What is the helicotrema?

A

Apex of Cochlea - where the Scala Vestibuli and Scala Tympani meet

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11
Q

What is the hearing sense organ, where is it and what does it consist of?

A
  • Organ of Corti/ Spiral Organ
  • Lies on Basilar Membrane of the membranous labryrinth
  • Consists of Inner and Outer Hair Cells topped with stereocilia or stereovilli
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12
Q

What is the function of the
a) Reissner’s Membrane
b) Basilar Membrane

A

a) Separate the scala vestibuli from scala media
b) Sepaates the scala media from scala tympani; determines mechanical wave propagation properties of cochlear

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13
Q

Describe the physiology of sound transmission through the ear (until picked up by CN)

A

1) Sound waves collected by outer ear, chanelled to tympanic membrane
2) Transmitted along the middle ear ossicles (malleus, incus, stapes) - stapes vibrates the oval window
3) Sound waves are converted into perilymphatic pressure in the scala vestibuli
4) Transmitted through the vestibular membrane to the basilar membrane
5) Organ of Corti set into motion and stimulated - converted into electric stimuli picked up by CN8
6) Perilymphatic pressure spreads onto scala tympani and transmits pressure to the round window

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14
Q

Describe the tonotopic map of sound frequency occuring along the basilar membrane

A

Base of Basilar Membrane: Narrow and Stiff - more sensitive to high frequency sounds

Apex of Basilar Membrane: Wide and Floppy - Sensitive to Low Frequency Sounds

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15
Q

Describe the auditory pathway from CN to the brain

A

1) Hair cells to Cochlea Nerve (CN8) (1st order sensory neuron via Cochlear Ganglion – no synapse bc pseudounipolar)
2) CN8 travels through the internal acoustic meatus
3) To brainstem (pontomedullary junction)
4) Synapse at cochlear nucleus (2nd order neuron), then decussate
5) Encounters Superior Olivary Nuclei (pons) then Inferior Colliculus (midbrain) [decussation occurs throughout]
6) reaches the medial geniculate nucleus in the thalamus
7) goes to primary auditory cortex (superior temporal gyrus (Heschl’s Area))
8) Heschl’s Area communictaes with Wernicke’s Area (sensory speech area for interpreting language, music etc.)
9) Wernicke’s Area may communicate with Broca’s Area (motor speech area)

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16
Q

What is the function of
a) Superior Olivary Nucleus (SON)
b) Inferior Colliculus (IC)

A

a) Responsive to differences in intensity and timing between sounds entering ear simultaneously - helps in localisation of sounds in space
(give rise to both ipsilateral and contralateral fibres)
b) integrates spatial info from SON, intensity and pitch information from cochlear nucleus

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17
Q

How does auditory modulation work?

A

Reciprocal connections between auditory cortex, MGN, and IC

IC, SON and Lateral Lemniscus send fibres back to dorsal and ventral cochlear nuclei

Fibres (from SON & TB) and reticular formation also terminate on hair cells fo organ of Corti

  • feedback mechanism for regulating selective attention to certain sounds
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18
Q

How does dampening of one’s own voice happen?

A
  1. Fibres enter the V & VII motor nuclei to link with motor neurons supplying tensor tympani and stapedius muscles in the middle ear
  2. These muscles exert a dampening action on middle ear ossicles

*tensor tympani activated by ones own voice and stapedius by external sounds

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19
Q

How does startle reflex work?

A

Loud unexpected sounds cause flinching - reflex is mediated by reticulospinal fibres and fibres to the VII motor nucleus

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20
Q

How does a cochlear implant work?

A
  1. External speech processor captures ambient sounds and converts them into digital signals
  2. Signals are transmitted to an internal implant under the skin
  3. Implant converts the signals into electrical impulses, which are sent to an electrode array inserted into the cochlea
  4. Electrodes stimulate the auditory nerve, and brain perceives signals as sound
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21
Q

What are the components of the vestibular system? What are their functions?

A
  1. Vestibule (Utricle & Saccule) – Detect Linear Acceleration (static) - position of head
  2. Semi-circular Canals (Anterior, Posterior, Lateral) – Angular Acceleration (rotation) - movements of the head
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22
Q

What are the receptors in the vestibular system called?

A

Saccule & Utricle: Hair Cells in Maculae
Semicircular Canals: Hair Cells in the Cupula of the Cristae Ampullaris

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23
Q

How does the maculae appear?

A

Cilia from hair cells are embedded in a gelatinous matrix of the otolithic membrane containing otoliths (composed of calcium carbonate crystals) (within the saccule & utricle)

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24
Q

How does the saccule & utricle perform its function?

A

When head moves with reference to gravity, otolithic membrane shifts and hair cells in the macula detect this movement and sends information along the vestibular nerve to the brain for interpretation (“which way is up”)

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25
Q

How does the crista ampullaris appear?

A
  1. Inside the ampulla is a crest (crista ampullaris) on which hair and supporting cells are located. Cilia of hair cells are embedded in the gelatinous mass (cupula)
  2. Stereocilia projecting from the apical surfaces of all hair cells & a single kinocilium at the edge of the apical surface
  3. Displacement of the cupula will results in excitation/inhibition of the hair cell
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26
Q

How does the semi-circular canals & crista ampullaris perform its function?

A

Upon rotational movements, the endolymph moves (albeit lagging behind due to inertia), pushing the cupula over and stimulating the hair cells

this sends information to the vestibular nerve

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27
Q

What is the pathway of the vestibular nerve to the brain?

A

Scarpa’s ganglion to enter the brainstem to vestibular nuclei

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28
Q

What are central pathways of the CN8?

A

Vestibular Nuclei to
a) Cerebellum: signals relayed back as muscle movements of the head, eyes and posture
b) Nuclei of CN3, 4, 6: Related to Vestibular-Ocular Reflex (VOR), allowing for eyes to fix on a moving object while staying in focus
c) Spinal Cord (vestibulospinal tract): To allow quick reflex reactions to both limbs and trunk to regain balance
d) Reticular Formation: Signal the new body psoture and how to adjust circulation and breathing
e) thalamus: allow for head & body motor control as well as being conscious of body position

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29
Q

How does the vestibulo-ocular reflex work?

A

A rotation of the head is detected, which triggers an inhibitory signal to extraocular muscles on one side, and an excitatory signal to the muscles on the other side – compensatory movement of the eyes

30
Q

3 clinical disorders associated with the vesitbular system?

A
  1. Nystagmus: Fast uncontrollable movements of the eye
  2. Vertigo: Caused by movement of the fluid in the semi-circular canal
  3. Motion Sickness: afferents from the vestibular system activate their projections to the reticular formation in pons and medulla, subsequent activation of autonomous centres results in motion sickness
31
Q

WHat are 3 conditions that determine balance?

A
  1. Proprioception
  2. Vestibular System
  3. Vision
32
Q

What bone is the roof of the middle ear?

A

Petrous part of the temporal bone

33
Q

What sits on top of the roof of the middle ear?

A

The mater of the brain & the brain

34
Q

What is the significance of the floor of the middle ear?

A

The internal jugular vein moves right inferior to it (from medial to lateral after passing through the jugular foramen) ps: jugular foramen is along the medial side of the temporal bone

35
Q

What is the significance of the floor of the middle ear?

A

The internal jugular vein moves right inferior to it (from medial to lateral after passing through the jugular foramen) ps: jugular foramen is along the medial side of the temporal bone

36
Q

What makes up the promontory of the middle ear?

A

The base of the cochlea

37
Q

What parts are there on the medial wall of the middle ear?

A
  1. Promontory
  2. Oval Window
  3. Round Window
38
Q

What parts are there on the posterior wall of the middle ear?

A
  1. Aditus to the Mastoid Antrum (where the mastoid air cells are)
  2. Facial Canal containing the facial nerve passes across from the posterior wall to the medial wall of the middle ear
  3. pyramidal eminence which is the origin of the stapedius muscle (attachment to the stapes)
  4. Chorda Tympani nerve (branch of the facial nerve)
39
Q

What is the course of the chorda tympani?

A

branches off the facial nerve in the facial canal between the posterior wall of the middle ear and mastoid part of the temporal bone; travels across to the anterior wall of the middle ear (between incus and malleus); passes through the petrotympanic fissure then hitchhikes onto the lingual nerve

40
Q

What are the key parts of the anterior wall of the middle ear?

A
  1. Opening to the eustachian tube
  2. Opening for the tensor tympani (origin malleus, insertion eustachian tube)
  3. Tympanic Branch of the Internal Carotid Artery
  4. Deep Petrosal Nerve
  5. Lesser Petrosal Nerve
  6. Chorda Tympani Exit
41
Q

What nerve fibres are there on the promontory?

A
  1. Lesser Petrosal Nerve
  2. Tympanic Branch of the Glossopharyngeal nerve
  3. Branch from internal carotid plexus
42
Q

What is the course of the lesser petrosal nerve?

A
  • formed on preganglionic parasympathetic fibres of the tympanic plexus coalesce in middle ear
  • to exit temporal bone, moves through lesser petrosal hiatus, next to greater petrosal hiatus, runs anteriorly along middle cranial fossa, exits through foramen ovale
  • ends when it synapses in otic ganglion (located just extracranially from foramen ovale)
43
Q

What canal is anterior to the anterior wall of the middle ear?

A

Carotid Canal

44
Q

What is the course of the greater petrosal nerve?

A
  • originates from the geniculate ganglion (in the petrous part of the temporal bone, between the internal acoustic meatus and facial canal)
  • passes anteriorly through the greater petrosal hiatus, along the middle cranial fossa, exits through the foramen lacerum
  • joins with deep petrosal nerve to form nerve of the pterygoid canal
45
Q

What is the course of the nerve of the pterygoid canal?

A
  1. Originate from the merging of greater petrosal nerve and deep petrosal nerve
  2. Pass through foramen lacerum and then pterygoid canal
  3. Ends at the pterygopalatine ganglion in the pterygopalatine fossa (located on the palatine bone, posterior to the maxilla)
46
Q

What are the boundaries of the pterygopalatine fossa?

A

Anteriorly: Superomedial surface of the posterior surface of the maxilla
Posterior: Root of the pterygoid process of the palatine bone + anterior surface of greater wing of sphenoid
Medial: Upper part of the perpendicular plate of the palatine bone + orbital & sphenoidal processes of the palatine bone

47
Q

How is the deep petrosal nerve formed?

A

Branches from the sympathetic plexus of the internal carotid artery

48
Q

Which bone is the pterygoid canal located in?

A

Sphenoid Bone

49
Q

What is the course of the facial nerve?

A
  • origins at the pontomedullary junction
  • runs laterally into the internal auditory meatus, synapses at the geniculate ganglion (located between the internal acoustic meatus and the facial canal) and then into the facial canal
  • facial canal runs across from the medial wall to the posterior wall of the middle ear
  • facial canal then runs between the mastoid part of the temporal bone and the posterior wall of the middle ear
  • exits via the stylomastoid foramen (located slightly inferomedial to the external acoustic meatus, between the styloid process & mastoid part of the temporal bone)
50
Q

What is the arterial supply of the middle ear?

A
  1. Anterior Tympanic Branch of Maxillary Artery (branch of External Carotid Artery)
  2. Posterior Tympanic Branch of Stylomastoid branch of the posterior auricular artery
  3. Petrosal and Superior Tympanic Branches of the Middle Meningeal Artery
  4. Branches of ascending pharyngeal artery
  5. Tympanic Branches of the Internal Carotid Artery
51
Q

What is the course of the maxillary artery?

A
  1. Origins from the external carotid artery
  2. Passes around the neck of the mandible, then passes laterally, through the infratemporal fossa
  3. Passes round the inferior head of the lateral pterygoid muscle, enters pterygopalatine fossa
52
Q

What is the course of the middle meningeal artery?

A

Ascends in infratemporal fossa, and enters the middle cranial fossa via foramen spinosum

53
Q

What are the boundaries of the infratemporal fossa?

A

Anteriorly: Posterior surface of body of maxilla
Posteriorly: Styloid Process of Temporal Bone
Medial:Lateral Pterygoid Plate
Roof: Infratemporal surface of the greater wing of sphenoid
Lateral: Ramus of the Mandible

54
Q

What are the embryological origins of
a) External Ear Canal
b) Tymapnic Membrane
c) Eustachian Tube
d) Ossicles

A
55
Q

How does the inner ear form embryologically?

A

a) Starts at day 22-24
b) Surface ectoderm overlying site of future ear starts to thicken to form the otic placode
c) Invaginates into the mesenchyme below to form otic vesicle and eventually otal cyst

56
Q

What is the function of the external ear?

A

Amplication via the pinna and external ear canal

57
Q

What is the function of the middle ear?

A

An impedance transformer. sound energy in air to sound energy in water

58
Q

What is impedance? Higher in liquid or air?

A

Resistance by a medium to flow of sound waves. Liquid

59
Q

What is the important formula relating reflection co-efficient?

A
60
Q

How does the middle ear correct impedance?

A
  1. TM to oval window ratio
    - 20:1 so sound picked up by TM is amplified 20x
  2. Lever Action of Ossicles
    - malleus and incus positioned in lever like style
    - malleus is slightly longer than incus: small force applied to the malleus results in larger force transferred to incus (ratio abt 1: 1.3)
  3. Buckling Action of TM (2x amplification)

all in all amplifies sound by 52x (20 x 1.3 x 2)

61
Q

What is the structure of the cochlear hair cells? What are their functions?

A

3 rows of outer hair cells - amplifies sounds & signal modulation

1 row if inner hair cells - main signal transducer
1 row of inner hair cells

62
Q

What is at the end of the cochlear hair cells?

A

Stereocillia - linked to each other by tip link.
Tip link stretches when fluid moves over, opens K+ channels, influx ofK+ causes depolarisation, calcium channels open, release of neurotransmitters (glutamate) and hence activation of action potential to auditory nerve

63
Q

How is composition of K+ regenerated to ensure gradient is still there for action potential generation?

A

Stria vascularis contains many ion channels to reset K+ gradient

64
Q

Is the primary auditory cortex tonotopically tuned?

A

yes. higher frequencies more medial, lower frequencies more lateral

65
Q

why can sounds invoke emotion?

A

primary auditory cortex and wernicke’s area connected to amygdala

66
Q

How to test hearing?

A
  1. Tuning fork (512hz)
  2. audiometry testing (graphical representation
  3. behavioural hearing tests
    - audiometry
  4. objective tests
    - auditory brainstem response
    - otoacoustic emission testing
67
Q

Explain tuning fork tests and its relation to conductive or sensineural hearing loss

A
68
Q

What are common causes of conductive hearing loss?

A

Otitis Media with Effusion

Ear wax
Insects (foreign bodies)
cholesteatoma (an abnormal collection of skin cells deep inside your ear)
Trauma - causing perforated ear drums or dislocation of ossicles
otosclerosis

69
Q

How to treat conductive hearing loss caused by otitis media with effusion?

A
  1. Treat cold or nasal congestion
  2. If not better, myringotomy and tube insertion
70
Q

What are reasons for sensineural hearing loss

A
71
Q

Hearing Aids vs Cochlear Implants?

A

HA:
1. Frequency specific amplification
2. Adjustment & fine tuning from audiologists
3. connectivity
CI:
1. For profound hearing loss
2. Directly stimulate spiral ganglion cells of auditory nerve

CNS (7 decks)

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