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Y2 - NMH > Sound Conduction and Transduction > Flashcards

Sound Conduction and Transduction Flashcards

1
Q

Main causes of hearing loss?

A
  1. Loud sounds
  2. Some genetic diseases
  3. Infections e.g. Rubella, Syphilis
  4. Certain drugs e.g. chemo
  5. Age
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2
Q

Define pitch

A

Perception of frequency

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3
Q

Define timbre

A

What distinguishes between sounds at the same frequency and intensity

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4
Q

What is impedance?

A

The reluctance of a system in recieving energy from a source

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5
Q

Define resonant frequency

A

The frequency at which the impedance is minimal

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6
Q

What is conductive hearing loss?

A

When the ear is incapable of transmitting the vibration of sound waves onto the cochlea

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7
Q

Give 4 causes of conductive hearing loss

A
  1. Fluid accumulation in middle ear e.g. colds in children
  2. Perforated tympanic memmbrane
  3. Otosclerosis - abnormal bone growthj obstructing ear canal
  4. Barotrauma - temporary
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8
Q

How is vibration of the basilar membranes generated?

A
  • Motion of the stapes
  • Generates pressure difference between the 2 liquid-filled chambers of the cochlea
  • This causes basilar membrane vibration
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9
Q

What are the components of the organ of Corti?

A
  • Tectorial membrane
  • Basilar membrane
  • Hair cell
  • Supporting cell
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10
Q

How is the basilar membrane adapted to pick up sounds at different frequencies?

A
  • Heterogenous mechanical properties
  • The impedance of the basilar membrane varies along its length, meaning that so does the local resonant frequency - so it vibrates differently along its length in response to different frequencies
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11
Q

What is the process of mechano-transduction?

A
  • Note hair bundle = collection of stereocilia joined by tip links on hair cells
  • Sound stimulus causes bending of stereocilia towards the tallest stereocilium
  • So by the sliding of the stereocilia, the tip links are moved and this causes ion channels opening
  • This causes the internal voltage of the hair cell on which the stereocilia rest to change
  • Thereby this produces an electrical signal which travels to the brain
  • There is also the active process of hair cells bending with the stimulus direction causing negative stiffness in the tip links
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12
Q

Outline the 4 aspects of the active process of stereocilia movement alongside passive movement in response to sound stimuli that make it differ from a model of a purely passive basilar membrame with just the passive movement

A
  1. Amplification - A particular segment of a living basilar membrane (red curve) vibrates far more in response to its resonant frequency, than a dead BM
  2. Selective frequency tuning - A dead basilar membrane produces a broad response and it is not tuned for a specific frequency (blue curve). A living BM instead selectively amplifies single frequencies
  3. Compressive non-linearity - The motion of the BM is augmented 100-fold during low-intensity stimulation, but amplification diminishes progressively with the increasing intensity of the stimulus
  4. Spontaneous otoacoustic emission - ears emit a sound
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13
Q

What is the difference in the functions of the inner and outer hair cells?

A
  • Inner hair cells have afferent projections (go to the brain to provide sensory transduction)
  • Outer hair cells have efferent projections
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14
Q

What is electromobility and what does it cause that is thought to be an aspect of the active process of stereocilia / hair cell bundle movement in mechano-transduction and what does activation of it cause that is also characteristic?

A
  • When efferent fibres to outer hair cells are activated, frequency sensitivity and selectivity are enhanced
  • Impulse from the brain via efferent fibres causes voltage change in outer hair cells
  • This reorientates the protein ‘prestin’ - causing cell body shortening and elongation
  • This is electromobility
  • The movement causes the otoacoustic emissions
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15
Q

Describe how afferent signals upon detection of a sound stimulus can be transmitted to the brain via inner hair cells (IHCs) after the whole process of mechano-transduction. Include mention of the tonotopic map. Ignore the rest of the neural pathway from the cochlear nucleus until the primary auditory cortex

A
  • Mechano-transduction occurs and ultimately sends an impulse from inner hair cells via afferent fibres
  • IHCs synapse with sensory neurones in the cochlear ganglion - there are multiple fibres projecting from a single IHC
  • Ganglion cells in a particular region of the spiral ganglion respond best to the resonant frequency of the basilar membrane in the same area - tonotopic map
  • From cochlear ganglion cells along the axons in the cochlear nerve which transmits information to the cochlear nucleus
  • Each axon is responsive to a unique frequency
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16
Q

Describe the population phase-locking theory for why we need so many nerve efferent fibres projecting from a single IHC

A
  • Many efferent fibres must project from the same IHC in order to produce a phase-locked response
  • I.e. a response that happens at the same time as the ‘cycle’ (or stimulus)
  • By having many fibres, you can have a collective response to pick up the complete stimulus even at high frequencies i.e. if one fails to pick it up at one point, another picks up the slack - like all working together to paint different parts of a picture to make a whole picture
17
Q

1) What is sensorineural hearing loss?
2) Give some causes of sensorineural hearing loss?

A

1)

  • Problem in sensory apparatus of inner ear
  • Problem in vestibulocochlear nerve (retrocochlear nerve)

2)

  • Loud noise
  • Menieres disease - excess fluid in cochlea
  • Genetic mutation affecting organs of corti
  • Aminoglycoside antibiotics toxic in hair cells
  • Congenital disease e.g. rubella, toxoplasmosis
  • Ageing
18
Q

Go over the neural pathway starting from the cochlear nucleus all the way to the primary auditory cortex

A
  1. From the cochlear nucleus in the brainstem ipsilaterally, where its arranged tonotopically, with high frequencies dorsally along the cochlear nucleus and low frequencies ventrally
  2. Then along the superior olivary nucleus (from dorsally and not from ventrally) → then to the nuclei of lateral lemniscus (or directly if from ventral part of cochlear nucleus) → inferior colliculus → medial geniculate nucleus → primary auditory cortex
19
Q

How is the interaural time difference communicated and what part of the brain has this function?

A
  • Bushy cells in the medial superior olive
  • A map of interaural delay can be formed due to delay lines
  • A chronotopic map is formed using the delay lines. The neurone only fires once it recieves input bilaterally and simultaneously
  • The 2 inputs must essentially meet or ‘collide’
  • They travel along different paths of different distance arranged vertically and so if where thry meet is indicative of the interaural time difference (watch lecture clip for better visualisation)
20
Q

How is the interaural level difference communicated and what part of the brain has this function?

A
  • Lateral superior olive
  • Neurons are excited by sounds arising from the ear in the same side (ipsilaterally), while they are inhibited by opposite sounds (contralaterally)
21
Q

1) What part of the superior olivary nucleus sends feedback to the hair cells - and to which hair cells?
2) What is the function of providing feedback?

A

1)

  • Medial superior olive → IHCs
  • Lateral superior olive → OHCs

2)

  • Reduce cochlear sensitivity
22
Q

In the inferior colliculus, which ascending pathways converge, and amongst them, which is tonotopically arranged?

A
  • Central nucleus - tonotopically arranged
  • Dorsal cortex
  • External cortex
23
Q

What is the primary processing function of the inferior colliculus neurones in regards auditory information?

A
  • Precedence effect - localising sound
24
Q

What is mapped in regards auditory information in the primary auditory cortex?

A
  • Tonotopically mapped
  • Loudness mapped
  • Rate mapped
  • Frequency modulation mapped
25
Q

What is the primary processing function of the superior colliculus neurones in regards auditory information and what it does with the info?

A
  • Here auditory and visual maps merge
  • The auditory map created is fundamental for reflexes in orienting the head and eyes to acoustic stimuli

Y2 - NMH (12 decks)

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