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Me2ds0ci6 > Lecture 14 hearing I > Flashcards

Lecture 14 hearing I Flashcards

1
Q

The human ear recognises sounds frequencies in a range of …….

Sounds below 20Hz

Sounds above 20000 Hz

A

20 Hz to 20000 Hz

Infrasounds

Ultrasounds

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2
Q

The audiometry curve for a normal hearing person shows

What forms the auditory field?

Auditory threshold is….. while perception limit is……

What is the range for conversations area?

If there is damage in the conversation area,

A

The perception limit and auditory threshold for each frequency

The perception limit and auditory threshold

Lowest intensity that can be heard for a frequency…..highest intensity that can be perceived at a frequency

300Hz to 3 kHz (frequencies useful for human interactions).

The ability to conversate with others is affected

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3
Q

Parts of the external ear
Pinnacle/Auricle:
Concha:
Ear canal:
Ear drum(tympanic membrane):

What does the external ear do?

A

-diffracts and focus sound waves into the ear canal
- entry to ear canal. A resonator
- A resonator
- cause inner ear perilymph movement, vibrate -> change sound pressure levels.

Capture sound

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4
Q

Sound localisation and external ear

A
  • uses both ears to determine time delay when sound reaches one ear to another
  • Horizontal direction sound localisation cue: time delay & intensity difference
    -maximum time difference between ears : 760µsec
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5
Q

Middle ear
1. What is the middle ear
2. The middle ear ossicles …..
3. 3 bones (MIS) and 2 muscles (ST)
4. 3 bones form…. They are attached to… They are connected to each other by
5. 2 windows into cochlea

A
  1. An air filled pouch with 3 bones and 2 muscles
  2. Amplifies sound
  3. Malleus, incus, stapes and stapedius muscle, tenor tympani muscle
  4. Ossicular chain. Tympanic membrane. Ligamentous connection
  5. Oval window and round window
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6
Q

middle ear
1. What does the ossicular chain do?
2. What is the attenuation reflex by the stapedius and tenor tympani muscles

A
  1. Transmits sound vibration (low impedance [air] environment) from the tympanic membrane to the fluids in the inner ear (high impedance [fluid] environment)
  2. The muscles become rigid when there is loud sound to decrease movement of the ossicular chain to reduce damage.
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7
Q

Describe the movement of sound from the ear canal to the cochlea

A

Sound vibration through the ear canal moves the tympanic membrane which makes the ossicular chain move. The stapes that is in contact with the cochlear fluid moves the perilymph making the basilar membrane move. The round window bulges

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8
Q

inner ear
1. Consists of the (balance organ) and the (hearing organ)
2. Similarities and relationship

A
  1. Vestibule and semicircular canals, cochlea
  2. Same embryonic origin, communicate with each other, have sensory hair cells
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9
Q

Describe the cochlea (openings, structure, compartments, arrangement)

A

Round window covered by a membrane, oval window (stapes inserted into)

Hollow structure with three fluid filled compartments (Scala vestibuli, Scala media, Scala tympani) and the organ of Corti.

2-4 turns that surrounds the modiolus(central body structure) which contains auditory nerve & blood vessels.

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10
Q

Cochlear compartments and their information

A
  • Spiral ganglion: where sensory hair cells receive innervation from primary auditory neurons
  • Scala vestibuli and scala tympani: filled with perilymph (ECM with high Na+ & low K+ conc)
  • Scala media: filled with endolymph ( high K+ and low Na+ conc)
  • Basilar membrane: between Scala media and Scala tympani
  • Organ of Corti: main sensory organ on basilar membrane, sensory cells (sensory transduction) & supporting cells [epithelial cells] (metabolic & structural support for cochlea)
  • Stria vascularis: secretory epithelial tissues in 3 layers, important - secrete K+ into endolymph -> main driving force for sensory transduction to generate endocochlear potential
    -spiral ligament: made of fibrocytes (connective tissues), structural metabolic support to stria vascularis
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11
Q

Inner ear fluids
The endocochlear potential
- is __.
- depends on active __ of __ ions by the ___ ___.

When (_____), the electrochemical gradient is provided,…..

A

+ 80mV

Secretion…..K+….. Stria vascularis

Opening transduction channels of the sensory hair cell which drive k+ ions into the cells leading to depolarisation

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12
Q

Organ of Corti (components, covering)

A

On the basilar membrane and covered by tectorial membrane from apex to base.

Sensory hair cells (outer hair cells [OHC], inner hair cells [IHC]) with stereocilia, rods of Corti, basilar membrane, tectorial membrane, modiolus, spiral ganglion, auditory nerve, rods of Corti, Pillar cells, Deiters’ cells, afférent nerve, efferent nerve.

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13
Q

Organ of Corti part 1
1. Sensory hair cells is innervated _____by ______ in the ___ ___ ___.
2. The tectorial membrane is ….. (contact)
3. Inner hair cells (IHC) are __ shaped, make up____of the sensory hair cells and ___ to__.
4. Outer hair cells (OHC) are ____ shaped, arranged in __ and make up ___ of total sensory cells. They are the ___ & have high _____ and ____ to sound.
5. OHC have a motor protein in the lateral membrane,___, which ___cells to ________ in response to sound, leading to a _____ increase in sound.
6. The basilar membrane is the….

A
  1. Afferently….spiral ganglion neurons (SGN)….. osseuos spiral lamina.
  2. …..directly in contact with the stereocilia
  3. …oval …….~ 25% ….. send info to brain.
  4. …cylindrical …… three rows …. ~ 75%. …..cochlear amplifier….. sensitivity…..high frequency selectivity.
  5. ….prestin…..contract……increase movement of Organ of Corti….. 40 - 50 dbs.
  6. The principal structure of analysis of sound frequencies.
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14
Q

Organ of Corti part 2
7. Pillar cells are ___. They ____ structure of Organ of Corti. If they bend, ____. Inner and outer pillar cells ___
8. Deiters’ cells are located ______ to form cups for ___. They give _____.
9. OHC & IHC need both ___ innervation.
10. Efferent innervation comes from _____ and sends _____. Efferent neurons come from ___. They are important for ___ to ____.
11. Afférent innervation from afférent neurons come from ______ and send ______. This is important for ____.
12. Hair cell stereocilia are site of _____. The ___ of stereocilia causes ___.

A
  1. ….supporting cells, …..maintain, organ collapses. ….form the tunnel of Corti.
  2. ….under OHC, …….. OHC to sit in. …..structural / metabolic support.
  3. Afférent & efferent
  4. ……brain auditory cortex….info to cochlea. …brain stem structures. …..OHC to change sensitivity in response to sound.
  5. ……SGN…….signals to the brain. ….IHC.
  6. …….Stretch activated transduction channels. ….déflexion…… channels to open.
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15
Q

Features of IHC and OHC

IHC features

OHC features

A

No regeneration. Hair cells loss - gradual hearing loss. Stereocilia on apical surface. Protrusions with actin scaffold

Arranged linearly in 1 row, ~ 4000, oval shaped

Arranged V -shaped in 3 rows , ~12000, cylindrical shaped

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16
Q
  • Transduction channels (auditory hair cells) are mechanically gated by stereocilia movement so the organ of Corti is
  • shorter length stereocilia,
  • length depends on
A
  • The site of mechanoelectrical transduction.
  • spécialise in higher frequency hearing.
  • what kind of frequency hearing the stereocilia spécialises in
17
Q

5 stages of sensory transduction in the organ of Corti of mammalian cochlea

Organ of Corti - mechanoelectrical transduction site

A
  1. Sound waves move basilar membrane upwards (excitatory movement) and downwards (inhibitory movement)
  2. OHC stereocilia deflected by tectorial membrane -> cell depolarised by K+ influx through transduction (MET) channels
  3. Reverse transduction/ electromotility. Depolarized OHC react by contracting, sending energy back to organ of Corti & amplifies Organ of Corti response to sounds
  4. IHC excited by tectorial membrane (Hensen’s stripe) -> IHC stereocilia activated & IHC dépolarise (forward transduction).
  5. IHC-auditory nerve synapse activated -> message sent to brain
18
Q

Stage 1 of sensory transduction (movement of basilar membrane)
- What causes the movement?
- what is excitatory direction?

A

movement of stapes at oval window, creating oscillation of perilymph fluid -> basilar membrane moves up (excitatory direction - when stereocilia is deflected to lateral wall ) -> open stretch activated transduction channels -> OHC dépolarisation -> oscillation starts -> resting position -> transduction channel close & basilar membrane move down -> stereocilia move in inhibitory direction towards modiolus -> hyperpolarisation

AP created transmitted by auditory nerves.
Sound transduction (cochlea) oscillate between dépolarisation & hyperpolarisation from -70mV.

19
Q

Stage 2: opening of méchano-electrical transduction at OHC
What is it?
What are the links between stereocilia?

A

Transduction channels at tip of OHC stereocilia open, translating sound vibration into bioelectrical message to brain.

Tip link: transduction site of shorter stereocilia connect straight horizontally to stereocilia behind

Lateral links : between adjacent stereocilia and cilia between rows.

20
Q

Stage 3: Electromotility (reverse transduction)

A
  • dépolarisation of OHC - contraction by prestin- activates electromotility
  • causes contraction of organ of Corti
  • amplifies sound but not report to brain
21
Q

Stage 4: IHC mechano-transduction (forward transduction)

A
  • IHC send signal to brain
  • Hensen’s stripe (tectorial membrane groove) movement -> deflection of IHC in excitatory direction -> transduction K+ channels open -> depolarisation -> voltage gated Ca2+ channel open -> vessels docking onto synaptic membrane -> released transmitted into synaptic cleft.
22
Q

Stage 5: IHC auditory nerve synapse activation

A

Neurotransmitter release from IHC synaptic region into synaptic cleft stimulates auditory nerve fibre and send info to brain

23
Q

Prestin on OHC contracts, increasing the movement of basilar membrane,….

A

….amplifying sounds, resulting in unparalleled sensitivity and frequency selectivity of mammalian cochlea.

24
Q

Why K+ induce dépolarisation in IHC but hyperpolarisation in all neurons?

A

K+ conc in endolymph very high compared to intracellular space so K+ move into intracellular space

25
Q

Innervation of organ of Corti
1. Spiral ganglion neurons
2. Afférent fibres
3. Efferent fibres
4. Type 1 neurons (SGN)
5. Type 2 neurons (SGN)

A
  1. Located in Rosenthal’s canal in Modiolus, innervate IHC
  2. Originate and innervation from SGN, respond differently to different frequencies. Provide frequency and intensity coding to auditory cortex
  3. From superior olivary cortex (brainstem), innervate OHC, regulate excitability based on brain auditory pathway feedback -> change in hearing sensitivity when sound levels change
  4. Multiple converge to one hair cell. Large myelinated. Synapse on IHC. 95% of SGN
  5. One innervate multiple hair cell. Small myelinated. Afférent innervation to OHC
26
Q

What are the neurotransmitters at the IHC synapse and describe them ?

What is a ribbon synapse and what does it enable?

How are AMPAR and NMDAR activated?

A
  1. Glutamate: principal neurotransmitter.
  2. Acetylcholine: inhibitory. Act on muscarinic acetylcholine receptors on afférent ending. No effect on IHC.

It is surrounded by many glutamate filled vesicles and simultaneous release and fast transmission of glutamate.

AMPAR: physiological events (abnormal sound levels), NMDAR: in noisy conditions because permeable to Ca2+ so activate apoptotic pathways

27
Q

Frequency discrimination by cochlea

A

-Sound vibration detected along frequency specific regions of the basilar membrane
-High frequencies are detect at base and low frequencies at the apex. (passive tonotopical arrangement )
- wave reach maximal amplitude at appropriate stimulation frequency position then rapidly declines as it goes to apex (“sea waves to shore”)

28
Q

Basilar membrane and tonotopic mapping of sound transduction

  • Basilar membrane :
  • high frequency characteristics
  • low frequency characteristics
  • Base features
  • Apex features
A
  • analyser of sound frequency
  • low energy, travel short distance -> dissipate at basal end
  • high energy, travel long distance -> dissipate at apical end
  • narrow and stiff
  • wide, floppy, thin
29
Q

Relation between characteristic frequency and position on basilar membrane is

Pure tones (low, medium, high frequency)

Complex sound analysis

A

Smooth, monotonic, logarithmic

Take up 1/3 basilar membrane in cochlea (apical, middle turn, basal turn)

Each component oscillate to specific region -> hair cell depolarise -> info sent, complex sound analysed in brain -> integrate to something perceivable.

Me2ds0ci6 (28 decks)

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