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CNS CLERKSHIP > Sensory Transduction, Auditory and Vestibular Systems > Flashcards

Sensory Transduction, Auditory and Vestibular Systems Flashcards

1
Q

What are the sensory receptors of both the auditory and vestibular systems?

A

Hair cells.

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2
Q

Where are auditory hair cells located?

A

Within the spiral Organ of Corti on the thin basilar membrane in the cochlea of the inner ear.

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3
Q

Outer hair cells mechanically amplify what?

A

Low level sound.

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4
Q

What is the function of inner hair cells?

A

Transforms sound vibrations of cochlear fluids into electrical signals to be relayed via the auditory nerve to the auditory brainstem and auditory cortex.

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5
Q

Deflection of hair cell stereocilia enables what?

A

The opening of mechanically gated ion channels to allow small +ve ions to enter the cells.

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6
Q

What is the neurotransmitter released by hair cells to stimulate peripheral axons of afferent neurons?

A

Glutamate.

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7
Q

The tonic release of glutamate allows for modulation of what?

A
  • Action potential frequency in response to stimulus.
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8
Q

What is a tip link?

A

Extracellular filaments connecting stereocilia to gate/close the TMC1 channel depending on cilia tilt.

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9
Q

Otolith organs/otocysts detect what?

A

Tilt and acceleration.

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10
Q

Semicircular canals detect what?

A

Rotational movement.

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11
Q

What separates scala media and scala vestibuli?

A

Reissner’s membrane.

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12
Q

What separates scala media from scala tympani?

A

Basilar membrane.

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13
Q

Describe transduction in the cochlea.

A

Hair cells on the sensory epithelium of the Organ of Corti bend to cause movement of the basilar membrane which vibrates the tectorial membrane to bend cilia of hair cells.

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14
Q

Where do scala tympani and scala vestibuli connect?

A

At helicotrema.

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15
Q

Where is perilymph continuous?

A

In scala tympani and vestibuli.

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16
Q

Scala tympani meets which window?

A

Oval.

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17
Q

Scala vestibuli meets which window?

A

Round.

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18
Q

Why is movement/pressure at the oval window accompanied by a complementary motion at the round window?

A

Due to incompressible fluid in the cochlea.

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19
Q

Where does scala media close off at?

A

The apex of the cochlea.

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20
Q

Which membrane of the cochlea is flexible and vibrates in sync with fluid movement?

A

Basilar membrane.

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21
Q

Width and flexibility of the basilar membrane determines what?

A

The distance a particular frequency travels i.e. a non-spatial parameter -> spatial representation.

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22
Q

Where are hair cells of the organ of corti located?

A
  • Between the basilar membrane and reticular lamina.

- Tips in the tectorial membrane.

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23
Q

There are 2 types of hair cells (inner and outer), separated by what?

A

The rods of Corti.

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24
Q

Where do hair cells synapse?

A

On bipolar neurons with cell body in the spiral ganglion.

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25
Q

Describe transduction after the tectorial membrane vibrates.

A
  • Cilia of hair cells bend and may cause neurotransmitter release.
  • Released neurotransmitters are captured in the nerve fibres.
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26
Q

Hair cells at different locations are maximally activated depending on what?

A

Frequency of sound waves.

- Hair cells are thus tuned to different frequencies.

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27
Q

When do hair cells fire most?

A

When they bend most.

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28
Q

The hair cell K+ current flows what way?

A

Inwards.

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29
Q

Endolymph has a higher than normal concentration of what in comparison to perilymph?

A

K+.

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30
Q

What is endolymph potential?

A

+80mV.

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31
Q

As endolymph potential is +80mV, what is the gradient across the stereocilia membrane?

A

120mV.

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32
Q

Why are hair cells slightly depolarised at rest?

A

Only a few transduction channels are open at resting potential.

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33
Q

What systems exist for reconstituting K+ in endolymph?

A
  • K+ channels.
  • Transporters.
  • Gap junction networks composed of 5 different connexins.
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34
Q

Mutations in the genes allowing for the reconstitution of K+ in endolymph can result in what?

A

Deafness.

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35
Q

What is the main source of afferent signal of the auditory nerve (CN VIII)?

A

Inner hair cells.

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36
Q

Approx. how many afferents supply an inner hair cell?

A

Around 10.

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37
Q

Describe the ratio of outer hair cells to afferent supply.

A

Multiple outer hair cells are innervated by a single hair cell.

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38
Q

Which type of hair cell primarily receives efferent input?

A

Outer hair cells.

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39
Q

Function of outer hair cells?

A
  • Control basilar membrane stiffness.

- Amplify membrane vibration.

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40
Q

which type of hair cell is more numerous?

A

Outer hair cells.

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41
Q

Outer hair cells are also referred to as?

A

Cochlear amplifier.

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42
Q

What is present in the basilar membrane and capable of changing the length of hair cell, thus changing the spatial relationship between the basilar and tectorial membranes?

A

Motor protein composed o “prestin”.

  • Expanded to increase distance between membranes.
  • Contract to reduce distance.
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43
Q

How do outer hair cells respond to sound?

A

A receptor potential and change in length.

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44
Q

What hypertension medication inactivates the basilar membrane motor protein?

A

Furosemide.

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45
Q

As the outer hair cells change in length, what happens to the basilar membrane?

A
  • Increased movement.
46
Q

Increased movement of the basilar membrane results in what?

A

Increased bending of the inner hair cells and transduction.

47
Q

The auditory nerve (CN VIII) uses what two mechanisms for frequency coding?

A
  • Place code.

- Temporal code.

48
Q

What is the place code theory?

A

Each pitch is allocated to a particular place along the basilar membrane. It assumes excitation of a particular place is due to a specific pitch.

49
Q

What is temporal code theory?

A

Believes location of activity on the basilar membrane irrelevant.
Pitch is coded by firing rate of nerve cells in the auditory nerve.

e.g. Low frequency tones cause slow motion waves of b.m. -> low firing rates of auditory nerve.
High frequency tones cause fast motion waves of b.m. -> high firing rates of auditory nerve.

50
Q

Briefly describe the pathway from the cochlea to the auditory cortex.

A
  1. Cochlea.
  2. Cochlear nucleus.
  3. Superior olive.
  4. Inferior colliculus.
  5. Medial geniculate body.
  6. Auditory cortex.
51
Q

CN VIII has branches to 3 cochlear nuclei, name them.

A
  • Dorsal cochlear nucleus.
  • Posteroventral cochlear nucleus.
  • Anteroventral cochlear nucleus.
52
Q

Describe tonotopy.

A

The spatial arrangement of where sounds of different frequency are processed in the brain.

Tones of similar frequency are represented in topologically neighbouring regions of the brain.

53
Q

Why do nerves transmitting information from different regions of the basilar membrane encode frequency tonotopically?

A

To ensure that each neuron innervates several different areas and neuron types.

54
Q

What parts of the central pathway of the auditory system locates sound sources in space?

A
  • Lateral superior olive.

- Medial superior olive.

55
Q

In the Central Pathway of the Auditory System, what is the principal relay to the cortex?

A

Medial geniculate.

56
Q

In the Central Pathway of the Auditory System, what identifies and processes complex sounds?

A

The auditory cortex.

57
Q

In the Central Pathway of the Auditory System, what forms the full spatial map?

A

The inferior colliculus.

58
Q

In the Central Pathway of the Auditory System, what starts sound feature processing?

A
  • Dorsal cochlear nucleus.
  • Postero-ventral cochlear nucleus.
  • Antero-ventral cochlear nucleus.
59
Q

What generates the “interaural time difference”?

A

Sound arising from the right is detected by the right ear before the left. Interaural time delay is the difference in time of sound arrival between the two ears.

60
Q

How may interaural time difference be detected?

A

Delay lines.

61
Q

The lateral superior olive receives excitatory input from what?

A

The ipsilateral anteroventral cochlear nucleus.

62
Q

The lateral superior olive receives inhibitory input from what?

A

Contralateral anteroventral cochlear nucleus input excites a neuron in the ipsilateral medial nucleus of the trapezoid body that then sends inhibitory signals to the LSO neuron.

63
Q

If aural signal is closer to the ipsilateral ear of the Lateral Superior olive, what will happen to the LSO?

A

It will undergo net depolarisation.

64
Q

If aural signal is closer to the contralateral ear of the Lateral Superior olive, what will happen to the LSO?

A

It will undergo net inhibition (hyperpolarisation).

65
Q

Each Lateral Superior Olive receives what from the:

  • Ipsilateral ear?
  • Contralateral ear?
A
  • Ipsilateral ear: net depolarisation.

- Contralateral ear: net hyperpolarisation (inhibition).

66
Q

An aural signal stimulates a Lateral Superior Olive neuron where?

A

From each hemisphere.

67
Q

Balance between excitatory and inhibitory neurotransmission of lateral superior olive determines what?

A

The net excitation forwarded to the inferior colliculus and lateral lemniscus.

68
Q

What is the Calyx of Held?

A

A large synapse in the auditory CNS.

69
Q

What makes synaptic transmission particularly reliable at the Calyx of Held?

A
  • Multiple sites of synaptic vesicle fusion.
70
Q

What benefit is offered by multiple sites of synaptic vesicle fusion in the Calyx of Held?

A
  • Fast, reliable synaptic transmission.

- -> Incoming presynaptic APs reliably trigger APs even at high input frequencies.

71
Q

Vestibular system provides information concerning?

A
  • Gravity.
  • Rotation.
  • Acceleration.
72
Q

The vestibular system is an important reference for what other systems?

A
  • Somatosensory system.

- Visual systems.

73
Q

Function of vestibular system.

A

Allows for:

  • Gaze and postural stability.
  • Sense of orientation.
  • Detection of linear and angular acceleration.
74
Q

What are the two basic questions answered by the vestibular organ?

A
  • What way am i going?

- What way is up?

75
Q

How does the vestibular organ sense head angular acceleration and rotation?

A

Semicircular canals.

76
Q

How does the vestibular organ sense head linear acceleration, translation motion and gravity?

A

Saccule and utricle.

77
Q

What is the “vestibular organ”

A

The peripheral sensory apparatus.

78
Q

Structure detecting and relaying information to the vestibular nucleus regarding the head’s angular and linear velocity to the central processing system.

A

Vestibular organ/peripheral sensory apparatus.

79
Q

Processes information in conjunction with other sensory inputs to determine position and movement of head in space.

A

Central processing system.

80
Q

Generates compensatory eye movements and compensatory body movements during head and postural adjustment.

A

Motor output system.

81
Q

Function of semicircular canals?

A

Detect head movements via rotatory acceleration.

82
Q

What is the crista of the semicircular canals?

A

Sheet of cells where hair cells are clustered.

83
Q

What is the ampulla of semicircular canals?

A

A bulge along the canals containing crista.

84
Q

The cilia of semicircular canals project into where?

A
  • Gelatinous cupula.
85
Q

Describe the orientation of kinocili of semicircular canals.

A

All are oriented in the same direction and are therefore all either excited or inhibited simultaneously.

86
Q

What fills the semicircular canals?

A

Endolymph.

87
Q

Movement of the head causes endolymph fluid to circulate within semicircular canals and displace what?

A

Cupula.

88
Q

If you excite the left horizontal canal of the SCCs, you inhibit what?

A

The right horizontal canal.

89
Q

If you excite the right horizontal canal of the SCCs, you inhibit what?

A

Left horizontal canal.

90
Q

If you excite the left anterior canal of the SCCs, you inhibit what?

A

Right posterior canal.

91
Q

If you excite the right anterior canal of the SCCs, you inhibit what?

A

Left posterior canal.

92
Q

If you excite the left posterior canal of the SCCs, you inhibit what?

A

Right anterior canal.

93
Q

If you excite the right posterior canal of the SCCs, you inhibit what?

A

Left anterior canal.

94
Q

Movement of the head to the left causes endolymph to move where and why?

A

To the right because of inertia.

95
Q

Otolith organs sense what?

A

Linear acceleration of head and change in orientation of head relative to gravity.

96
Q

What makes up the “otolith organs”?

A
  • Utricle and saccule.
97
Q

The saccule detects movement in which plane?

A

Vertical/sagittal.

98
Q

The utricle detects movement in which plane?

A

Horizontal.

99
Q

Hair cells in otolith organs are found where?

A

Macula.

100
Q

What divides the hair cells in the otolith organs?

A

Striola.

101
Q

Striola divides the hair cells in the otolith organs into what?

A

Two populations with opposing polarities.

102
Q

Crystals of what are found on the otolithic membrane?

A

Calcium carbonate.

- “Otoconia”.

103
Q

What is the function of Striola of the Macula?

A

Structural landmark arranging otoconia into narrow trenches and dividing each otolith (saccule and utricle).

104
Q

Describe the orientation of the hair cells in the macula.

A

Over the course of the macula, the orientation of hair cells changed to allow otolith organs multidirectional sensitivity.

105
Q

Name the 3 major vestibular reflexes.

A
  • Vestibulo-ocular.
  • Vestibulo-colic.
  • Vestibular-spinal.
106
Q

Describe the vestibulo-ocular reflex.

A

Keeps the eyes in place when the head moves.

Thus maintaining clear, stable vision during head movements.

107
Q

Describe the vestibulo-colic reflex.

A

Keeps the head in place/on a level plane when walking.

108
Q

Describe the vestibular-spinal reflex.

A

Adjusts posture during rapid changes in position.

109
Q

How does the vestibulo-ocular reflex maintain clear, stable vision during head movements?

A
  • Eyes move in opposition direction of head movement.
  • Speed of eye movement equal to that of head movement.
  • Keeps objects in focus during head movements.
110
Q

Name a drug that may cause ototoxicity.

A
  • Aminoglycoside antibiotics e.g. gentamicin.

- Chemotherapy agents.

111
Q

Alcohol enters the blood and then moves into the cupula, causing it to become?

A

Less dense and thus floats in endolymph more than usual.

112
Q

Alcohol causes the cupula to float in endolymph more than usual causing what?

A

Hair cells to bend as if you were rotating despite being still.

CNS CLERKSHIP (43 decks)

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