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LCRS Neuro > The Ear and Auditory Pathways > Flashcards

The Ear and Auditory Pathways Flashcards

1
Q

what is the action of the outer ear?

A

focuses sound onto tympanic membrane to create pressure waves

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2
Q

what is the action of the middle ear?

A

increases pressure of vibration:

1) focuses vibrations from larger tympanic membrane to the smaller oval window
2) incus with flexible joint with the stapes so the ossicles can use leverage to increase force onto the oval window

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3
Q

how are the ossicles protected when there are loud noises?

A

the stapedius and tensor tympani muscles contract when noise is loud

this restricts the movement of the ossicles to protect the inner ear

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4
Q

what is the function of the cochlea (inner ear) ?

A

transduce vibration into nervous impulses

produces a frequency/pitch and intensity analysis of the sound

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5
Q

what are the 3 compartments of the inner ear?

A

scala vestibul (contains perilymph fluid)

scala tympani (contains perilymph fluid)

scala media (contains endolymph fluid)

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6
Q

how does basilar membrane sensitivity change?

A

is sensitive to different frequencies at different points along its length

proximal, narrow and tough (close to oval window)
distal, broad and floppy (at the apex in the cochlea)

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7
Q

what is the function of the auditory tube in relation to the tympanic membrane?

A

allows equilibrium of air pressure on either side of the membrane

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8
Q

what is the organ of Corti?

A

collectively the hair cells surrounded by the supporting cells

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9
Q

what feature of the inner ear secretes endolymph?

A

stria vascularis

high K+, low Na+

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10
Q

how are inner hair cells arranged?

how many? rows? innervation?

A

3500 cells arranged in a single row

density innervated by ~10 sensory axons

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11
Q

how are outer hair cells arranged?

how many? rows? innervation?

A

20000 cells arranged in 3 rows

sparsely innervated by one axon for several cells

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12
Q

which of the two hair cell types transmit signals to the brain?

A

the inner hair cells

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13
Q

what is the effect of higher amplitudes on the stereo cilia?

A

greater deflection

K+ channel opening

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14
Q

mechanism of transduction

A
  1. Basilar membrane vibrates to sound.
  2. Upward movement displaces stercocilia away from modiolus:
    K+ channels open –> K+ enters from endolymph –> hair cell depolarises.
  3. Depolarisation opens Ca2+ channels in body of hair cell.
  4. Glutamate released from base depolarises axon of spiral ganglion cell –> action potential.
  5. Downward movement displaces stercocilia towards modiolus:
    K+ channels close –> hair cell hyperpolarises.
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15
Q

sensitivity of the transduction mechanism? how much deflection is required?

A

high sensitive

sound requires 0.3 mm deflection

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16
Q

what does the system depend on to remain sensitive?

A

the endolymph needs to maintained at +80mV by the stria vascularis

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17
Q

how do the spiral ganglion cells of the cochlea reach their ipsilateral cochlear nuclei?

A

via the vestibulocochlear nerve

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18
Q

what is the significance of the ipsilateral connection made by CN VIII?

A

all connections from the cochlear nuclei onwards are bilateral
deafness in one ear must be caused by problems in the cochlear nucleus or CN VIII

19
Q

hearing organisation in the brain

A

tonotopy is the spatial arrangement of where sounds of different frequency are processed in the brain. Tones close to each other in terms of frequency are represented in topologically neighbouring regions in the brain

20
Q

range of sound in humans

A

20-20000 Hz

21
Q

what range is human hearing most sensitive

A

1000-3000 Hz

22
Q

where do higher frequencies vibrate the basilar membrane?

A

closer to the base

23
Q

where do lower frequencies vibrate the basilar membrane?

A

closer to the apex

like a swimming jumping board, the end (apex) is least stiff and widest, the base is tough and narrow

24
Q

decibel scale

A

logarithmic
0–>120
60= conventional speech
120= thunder

ears response to sound is not linear

25
Q

hearing loss

A

with age

difficulty hearing the louder frequencies associated with speech (2000-5000 Hz)

26
Q

how is the tympanic membrane clinically evaluated?

A

otoscopy

27
Q

what does the tuning fork test enable you to do?

A

differentiates between conductive (outer/middle ear) and sensorineural (inner ear) hearing loss

28
Q

what is audiometry?

A

measuring the acuity for variations in sound intensity and frequency.

An audiometer produces sound of varying intensity and frequency and a pure tone audiogram can be generated to discover where the hearing loss is.

29
Q

what is tympanometry?

A

examination used to test conduction of middle ear, mobility of tympanic membrane and the conduction bones by creating variations of air pressure in the ear canal.

30
Q

what are the possible results on a tympanogram?

A

Tympanograms can commonly show;

  • A (normal compliance)
  • C (negative middle ear pressure)
  • B (non-vibration of tympanic membrane) – non-vibration of TM can be due to:
  • middle ear effusion
  • perforation of TM
  • Eustachian tube dysfunction - occluded ear canal.
31
Q

what is spontaneous otoacoustic emission?

A

OAEs are low-intensity sounds generated by the cochlea outer hair cells.

32
Q

3 types of hearing loss

A
  • conductive hearing loss (outer/middle ear problem)
  • sensorineural hearing loss (inner ear)
  • mixed hearing loss
33
Q

5 main causes of outer-ear conductive hearing loss

A

1) congenital malformation e.g. congenital atresia (collapse/closure of ear canal)
2) impacted wax
3) foreign bodies
4) external otitis
5) exostosis

34
Q

what is external otitis?

examples?

A

inflammation of the passage of the outer ear

e. g. otorrhea- abnormal fluid
e. g. pain in mobilisation of the ear and tragus–> systemic symptoms

35
Q

4 main causes of middle ear conductive hearing loss?

A

1) acute otitis media - inflammation of middle ear
2) otitis media with effusion- same but with fluid accumulation
3) chronic otitis media
4) otosclerosis

36
Q

the two forms of chronic otitis media (of middle ear)

A

1) no cholesteatomatous:
- without perforation or with perforations

2) cholesteatoma- destructive and expanding growth consisting of keratinising squamous epithelium in the middle ear and/or mastoid process

37
Q

what is otosclerosis?

A

soft, spongy growth of new bone mostly near the oval window

90% of cases, no symptoms
can reduce mobility of stapes –> hearing loss therefore perform stapedectomy

mostly affects women

38
Q

5 main causes of inner ear sensorineural hearing loss

A

1) prebyacusis- age related hearing loss
2) sudden hearing loss
3) ototoxic drugs
4) infections
5) noise-induced

39
Q

prebyacusis

A

Is gradual and symmetric and is due to the ageing European population.

It affects frequencies of speech for the 5th decade of life.

Men are 2x more affected and tinnitus is often associated.

40
Q

what is sudden hearing loss?

A

greater than 30dB hearing reduction over >3 contiguous frequencies, occurring over a period of 72 hours or less.

there is rapid unexplained loss of hearing usually in one ear

41
Q

examples of ototoxic drugs

A

diuretics
beta blockers
TCAs
antibiotics

42
Q

infections that can affect inner ear conductivity

A 
mumps
measles
chickenpox 
influenza
syphilis
43
Q

what are the two forms of noise-induced hearing loss?

A

1) acoustic trauma- brief exposure to very intensive sounds. Can cause severe hearing loss, but recovery can be great
2) long term noise exposure - common in occupational settings

LCRS Neuro (19 decks)

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