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ENT > Physiology of hearing and balance > Flashcards

Physiology of hearing and balance Flashcards

1
Q

What is the ion balance of perilymph?

A

Similar to ECF with a high sodium level and low potassium level

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2
Q

What is the ion balance of endolymph?

A

Similar to ICF - high potassium level and a low sodium level

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3
Q

What is the central pathway of hearing?

A 
E.coli Ma:
Eight nerve 
Cochlear nucleus
superior Olivary complex
Lateral lemniscus
Inferior colliculus
Medial longitudinal fasciculus 
Auditory complex (brodmanns area 41 and 42 of the left superior temporal gyrus)
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4
Q

What age can a foetus hear?

A

18 weeks

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5
Q

What age can a foetus respond to sound/ voice?

A

26 weeks

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6
Q

How is neonatal hearing tested?

A

Outer hair cells produce sound and therefore if they are functioning, it can be assumed there is a normal functioning cochlea

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7
Q

What is normal development in hearing in language in children?

A

3 months - cooing, recognize mother voice
6 months - babbling, turns to sound or eyes towards sound, makes happy and sad sounds
12 months - may make simple noises, mama/dada, follows instructions, turns to sound, follow simple instructions
18 months - few words, recognize body parts, animals, simple commands
24 months - two word phrases, 50+ words, understands questions and follows demands
36 months - 3 word sentences, understand order, positioning

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8
Q

When will a child be referred to a speech therapist if they are not speaking?

A

27 months

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9
Q

What are the 5 vestibular end organs?

A

Ampullae of 3 SCC (rotational movement)

Organs of otolith: saccule and utricle (linear movement)

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10
Q

What does the superior vestibular nerve supply?

A

Lateral and anterior SCC

Utricle

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11
Q

What does the inferior vestibular nerve supply?

A

Posterior SCC

Saccule

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12
Q

What does the stapedius muscle do and what supplies it?

A

Pulls stapes away from the oval window

Supplied by facial nerve

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13
Q

What does the tensor tympani muscle do and what supplies it?

A

Pulls the malleus, tensing the tympanic membrane

Supplies by V3

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14
Q

What is contained within the cochlear duct?

A

Endolymph (sacula media)

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15
Q

What is contained within the cochlea?

A

Perilymph (scala vestibuli and scala tympani)

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16
Q

What window is at the scala vestibuli?

A

Oval window

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17
Q

What window is at the scala tympani?

A

Round window

18
Q

What does the organ of corti sit on?

A

The basilar membrane of the scala medius (endolymph)

19
Q

Where is low pitch and high pitch sound heard?

A

Low pitch at the apex (longest radial fibres)

High pitch at the base (short radial fibres)

20
Q

Where are the afferent neurones of the cochlear nerve found?

A

Bipolar cell bodies in the spiral ganglion which is located within the modiculus

21
Q

How is sound transmitted from the outer ear to the inner ear?

A

Pressure waves impact the tympani membrane
Vibration transmitted from handle of malleus to incus to the stapes where the base rocks against the oval window to produce waves in the perilymph of the scala vestibuli

22
Q

How will the pressure wave move around the cochlea duct?

A

Perilymph of scala vestibuli
Endolymph of scala media - APs produced which travel to brain
Perilymph of scala tympani to leave cochlea via round window

23
Q

What effect will the pressure wave have on the basilar membrane?

A

It will impart a rocking action, proportional to the degree of displacement of the organ or corti. The stereocilia will be displaced, opening K+ channels leading to depolarisation of hair cells, releasing glutamate and firing an AP to the cochlear nerve

24
Q

What characteristics of the wave form determine pitch and volume?

A 
Pitch = frequency 
Volume = amplitude
25
Q

Where are the vestibular hair cells located?

A

The otolith organs (utricle and saccule) where they will detect linear movements of the head (saccule vertical and utricle horizontal)
3 SCC

26
Q

What movements do the otolith organs sense?

A

Linear - saccule vertical and utricle horizontal

27
Q

What movements do the ampullae of the 3 SCC (supeiror, lateral and posterior) detect?

A

Rotational, angular movements

28
Q

Where are the cell bodies of the vestibular nerve located?

A

Vestibular ganglion in the outer part of the IAM

29
Q

What occurs when the head rotates?

A

The endolymph will lag behind, exerting a pressure in the cupula in the opposite direction

30
Q

What hair cells are present in the vestibular system?

A

Kinocilium (tallest)
Bending of the stereocilia towards to kinocilium will depolarize the cell and result in an increased afferent activity
Bending away will hyperpolarize the cell

31
Q

Where can the macula of the otolith organs be found?

A

Patches of hair cells topped by small calcium carbonate crystals called otoconia
The saccule and utricle lie at 90 degrees so with any position of the head, gravity will bend the cilia of one macule due to the weight of the otoconia to which they are attached via a gelatinous layer

32
Q

Are the kinocilium in the macula oriented in the same way?

A

NO
In the utricle the kinocilia point towards to striola
In the saccule they point away from the striola

33
Q

Where do the axons of the 1st order vestibular afferents travel to after they synapse in the vestibular ganglion at the IMA?

A

Vestibular portion of the 8th CN through the IMa to enter the brainstem at the cerebellopontine angle

34
Q

What are the 4 2nd order vestibular nuclei?

A

Inferior, medial, lateral and superior

All found beneath the floor of the 4th ventricle

35
Q

What function does the lateral vestibulospinal tract have?

A

Walk upright - descends ipsilateral from where it originates.
Originates from the lateral vestibular nuclei

36
Q

What function does the medial vestibulospinal tract have?

A

Tracts bilaterally along the medial longitudinal fasciculus to track head movements and help to coordinate head movements with eyes (VOR)

37
Q

Describe inter-nucleus ophthalmoplegia?

A

Patients gaze directed AWAY from lesion, the ipsilateral (adducting) eye will not adduct and the contralateral (abducting) eye will demonstrate horizontal nystagmus

38
Q

What causes INO?

A

Lesion in the medial longitudinal fasciculus which provides a connection between CN3 in the midbrain and CN6 in the pons and facilitates conjugate eye movements on lateral gaze

39
Q

What can cause INO?

A 
MS - bilateral
Vascular brainstem lesion
Pontine glioma
Inflammatory encephalitis 
Myasthenia gravis
40
Q

What is nystagmus?

A

An imbalance of the CNS perceiving a rotating head due to vestibular loss on one side and a firing VOR, you come to the end of the orbit and saccade back
But then the brain still interprets rotating to the eye will flick back

41
Q

What are the fast and slow movements of a nystagmus?

A

VOR is slow moving outwards

It will quickly saccade (flick) back to the midline

ENT (20 decks)

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