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Neuroscience (own deck) > Auditory and Vestibular systems > Flashcards

Auditory and Vestibular systems Flashcards

1
Q

what is sound?

A
  • particles vibrate within a restrictred area
  • sound wave travels along whole length
  • rarefied (less particles) and compressed (more particles) air create the peaks and troughs of the sound wave
  • compressed = peak
  • rarefied = trough
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2
Q

what is the frequency of sound?

A
  • number of compressed and rarefied patches of air that pass by our ears per second
  • measured in Hz
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3
Q

what is the intensity/amplitude of sound?

A
  • the air pressure difference between peaks and troughs
  • measured in dBs
  • logarithmic scale
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4
Q

what is the frequency range of human hearing?

A

20-20000Hz

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5
Q

what are the 3 divisions of the ear?

A
  1. outer ear
    - from the pinna to the tymphanic membrane
  2. middle ear
    - from the tympanic membrane to the oval window
  3. inner ear
    - from the cochlea to the vestibular system
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6
Q

what are the properties of the human auditory system?

A
  • more sensitive to sounds in front than behind
  • convolutions of the pinna play a role in sound localisation
  • fixed in humans but mobile in other animals
  • auditory canal extends ~2.5cm into the skull
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7
Q

what is the basic mechanism of transduction of sound in the ear?

A
  • sound is funnelled through ear canal and hits the tympanic membrane
  • air is pushed and pulled, causing the tympanic membrane to oscillate
  • cochlea contains mechanoelectrical transducers which produce electrical signals from the oscillations
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8
Q

what are the 3 ossicles of the middle ear?

A
  1. Malleus (hammer)
  2. Incus (anvil)
  3. Stapes (stirrup)
  • malleus attaches to tympanic membrane and incus
  • incus attaches to stapes
  • stapes attaches to oval window

malleus to incus has rigid connection, incus to stapes has flexible connection

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9
Q

how does the middle ear and the tympanic membrane transfer sound?

A

inward movement of the tympanic membrane:
- membrane pushed by the compression phase of a sound wave

outward movement of the tympanic membrane:
- membrane pulled by the rarefaction phase of a sound wave

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10
Q

what is the role of the ossicles?

A
  • they amplify sounds to exert 20x more pressure on the oval window than on the tympanic membrane
  • this is to overcome the impedance of the cochlear fluid
  • stapes are pushed into oval window to generate pressure

oval would barely move if directly moved by sound due to the air-fluid interface
- fluid has greater inertia/impedance

ossicles ensures there is enough fluid movement in cochlea to generate signals

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11
Q

what is impedance matching?

A
  • air and water have different impedances

- they oppose movement brought about by a pressure wave differently

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12
Q

what is the anatomy of the cochlea?

A
  • cylindrical spiral
  • oval window attached to at the bottom and pushes fluid up the apex to the helicotrema
  • organ of Corti runs from base to apex and contains hair cells which are mechanoelectrical transducers
  • hair cells sit on basilar membrane
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13
Q

what are the 3 compartments of the cochlea?

A
  1. scala vestibula
    - where perilymph fluid is pushed though oval window
  2. scala tympani
    - where perilymph fluid is moved down
  3. scala media
    - filled with endolymph which has high potential due to positive ions
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14
Q

what is the difference between perilymph and endolymph?

A

perilymph:

  • low K+
  • 0mV

endolymph:

  • high K+
  • +80mV
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15
Q

what is the anatomy of the organ of Corti?

A
  • Outer hair cells (OHCs)
  • inner hair cells (IHCs) - primary transducers
  • both hair cells attach to stereocilia that stick upwards and transduce sound
  • they sit on the basilar membrane
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16
Q

what is the anatomy of the basilar membrane?

A
  • runs from base to apex of cochlea
  • flat when there is no sound
  • basilar membrane is disrupted by fluid from cochlea, and moves upwards and downwards
  • narrower and stiffer at base
  • wider and floppier at apex
  • has tonotopic response to different frequencies
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17
Q

what kind of frequency causes the base of the basilar membrane to move up?

A

high frequency sound

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18
Q

what kind of frequency causes the apex of the basilar membrane to move up?

A

low frequency sound

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19
Q

how is the basilar membrane like a travelling wave?

A
  • different frequency sounds cause maximal displacement of the basilar membrane in different regions
  • forms a tonotopic map
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20
Q

how does basilar membrane displacement affect hair cells?

A
  • causes stereocilia to move forward and backward
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21
Q

what happens to the basilar membrane when the stapes to move outward?

A
  • basilar membrane moves upward
  • tectorial membrane moves outwards
  • hair cells are pushed towards the taller stereocilia
  • hair cells depolarise
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22
Q

what happens to the basilar membrane when the stapes to move inward?

A
  • basilar membrane moves downwards
  • tectorial membrane moves inwards
  • hair cells are pushed towards shorter stereocilia
  • hair cells hyperpolarise
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23
Q

what are hair bundles connected by?

A

by tip links:

  • taller row of stereocilia at back
  • medium row in middle
  • short row at front
  • tip link filaments connect the three rows
24
Q

how do tip links work in the auditory system?

A
    • tip links can pull open mechanoelectrical transducer cation channels at the top of stereocilia
  • endolymph then moves into the channel, down the concentration gradient
25
Q

what happens to tip links under loud sounds?

A

the louder the sounds, the more overstimulated the tip links become
- they can break, so hair cells can no longer transduce sounds

26
Q

how do IHCs sense and transduce sounds?

A
  • stereocilia hair bundle is surrounded by endolymph
  • perilymph surrounds the hair cell body
  1. as sound wave comes in, hair cell is pushed towards taller stereocilia
  2. tip link is stretched, causing opening of mechanoelectrical cation channel
  3. K+ enters hair cell and depolarises it, generating a GP
  4. depolarisation causes opening of Ca2+ channels, and influx causes exocytosis of glutamate from vesicles
  5. EPSP is caused by glutamate binding to postsynaptic receptors on primary afferent neuron of auditory nerve
  6. EPSPs summate into AP
27
Q

what happens to IHCs when there is no sound?

A
  1. no sound waves mean hair cell is pushed towards the shortest stereocilia
  2. tip link is relaxed, so mechanoelectrical cation channel remains shut
  3. no K+ enters the hair cell, so no depolarisation occurs
  4. no exocytosis of glutamate, so no activation of primary afferent postsynaptic receptors
  5. no generation of EPSP so no summation to form an AP
28
Q

what is the function of OHCs?

A
  • they amplify sounds
  • they are electromotile so amplify movement so lower intensities can be heard
  • loss of OHCs causes loss of hearing of 30dB
29
Q

what is the point of the vestibular system?

A
  • understand where gravity is
  • help orientate you
  • recognise linear acceleration and rotational acceleration
30
Q

what does the vestibular system contribute to?

A
  • keeping our eyes still as we move
  • maintaining our upright posture
  • linked with the cerebellum for motor output and balance
  • enables us to perceive our own movement within a space
31
Q

what is the anatomy of the vestibular system?

A
  1. semicircular canals
  2. ampulla
  3. otolith organs
  4. Vestibular nerves
32
Q

what is the role of the semicircular canals?

A
  • horizontal part is for spinning in a horizontal plane

- anterior and posterior are for moving up or down

33
Q

what is the role of the ampulla?

A

where mechanoelectrical transduction hair cells are located

34
Q

what is the role of the otolith organs?

A

detect linear motion:

  1. utricle: detects movement in horizontal plane (forwards/backwards)
  2. saccule: detects movement in vertical plane
35
Q

what is the role of the vestibular nerves?

A

carry info from ampulla, utricle, saccule into CNS

36
Q

what fluid fills the vestibular labyrinth?

A
  • semicircular canals: filled with endolymph
  • utricle and saccule filled with endolymph
  • chambers either side of endolymph are filled with perilymph
37
Q

how do the hair cells work as sensory receptors in the vestibular system?

A

same principle as hair cells in auditory system, but respond to lower frequencies (0-20Hz)

  • vestibular hair cell contains a hair bundle at its top
  • hair bundles contain stereocilia
  • if there is no stimulus, the hair bundles are stood upright
38
Q

what happens to the vestibular hair bundles when there is a stimulus?

A
  1. hair bundles move towards taller stereocilia
  2. tip links are stretched, causing opening of mechanoelectrical cation channels
  3. K+ enters the hair cell and depolarises it, generating a GP
  4. GP causes opening of Ca2+ channels
  5. Ca2+ influx causes exocytosis of glutamate from vesicles
  6. glutamate binds to postsynaptic receptors on primary afferent neuron, causing depolarisation and EPSP generation
  7. EPSP summates to generate an AP
39
Q

how is the vestibular hair bundle structurally different to auditory hair cells?

A
  • cochlear IHC = 3 rows
  • vestibular hair cells = stereocilia are clumped together in a staircase structure

vestibular hair cells are easier to stimulate at lower frequencies

40
Q

what is the role of the kinocilium in vestibular hair cells?

A
  • kinocilium sets polarity of the hair bundle to determine gradient of hair bundle growth
  • the kinocilium is kept throughout life
41
Q

what are the 2 types of vestibular hair cell? what is the difference between them?

A
  1. Type I: large calyx (postsynaptic region which is expanded to encompass the whole hair cell)
  2. Type II: communicate with afferent nerve fibre by releasing neurotransmitter (normal synapse)

they have similar functional roles

42
Q

where are the vestibular hair cells found?

A

in sensory patches in the macula

  • taller stereocilia point towards striola on one side
  • smaller stereocilia point in the other direction
  • when one half is activated, the other half is inhibited
43
Q

what is the otolithic membrane? how does it work?

A
  • a gelatinous membrane
  • when tilted, the otoconia move and and drag the otolithic membrane with it
  • this pulls the hair cells towards the shorter stereocilia (causing mechanoelectrical transducer channels to shut - hyperpolarisation) or towards the taller stereocilia (causing channels to open - depolarisation)
44
Q

what is the otoconia in the vestibular system?

A
  • calcium carbonate crystals that add weight to the otolithic membrane
45
Q

how can vestibular input into the CNS be ambiguous?

A
  • the CNS doesn’t know how nerves have been activated
  • when the head moves to the left, the otoconia is dragged down
  • when the head moves to the right, the otoconia is also dragged down
  • endolymph and otoconia move as quickly as the body, so no matter the movement, the hair cells move and APs are generated
46
Q

how is AP firing determined to be due to head tilt or a movement to the right?

A

sensory systems integrate info to determine what movement we are doing:

  • vision helps distinguish what movement we are doing
  • proprioreceptors that detect stretch in the neck indicate what movement we do
47
Q

what is the anatomy of the ampulla?

A
  • endolymph in centre of ampulla
  • perilymph either side
  • hair cells located in middle of ampulla and project towards the cupula
48
Q

what is the cupula in the vestibular system?

A
  • a gelatinous structure penetrated by hair bundles
  • as endolymph is moved around, cupula moves left and right which excites/inhibits hair cells
  • cupula controls info that is sent down the vestibular nerve
49
Q

how do semicircular canals detect angular acceleration (rotation)?

A
  • inertia of endolymph during rotation displaces the cupula
  • if rotation to the left, endolymph moves to the right, so cupula moves to the right
  • hair bundles move to the right with the cupula
50
Q

how do the semicircular canals work in pairs?

A
  • horizontal canals on both sides lie in same plane so act as a pair
51
Q

what happens in the vestibular system as we turn to the left?

A
  • endolymph moves to right
  • one side of head is stimulated, other side is inhibited
  • this is due to hair bundles being orientated the same way on both sides
  • one the left side endolymph moves to right, so hair cells move towards taller stereocilia and are excited
  • on right side, hair cells move towards the shorter stereocilia, so they are inhibited
52
Q

what do vestibular organs input into?

A
  • vestibular organs input into vestibular nuclei in the brainstem
53
Q

what areas of the brain do the vestibular nuclei communicate with?

A
  • cerebral cortex: perceive movement
  • reticular formation: visceral response
  • oculomotor nuclei: adjust movement of the eye
  • spinal cord: change in posture, balance and muscle contraction
  • cerebellum: motor coordination and balance
54
Q

what is the vestibulo-ocular reflex?

A
  • when head shakes, vestibular system is activated due to rotation of semicircular canals
  • allows communication in the brainstem which sends info to oculomotor nuclei and ocular muscles
  • if head moves left, vestibular-ocular reflex causes contraction of eye muscles on right side
  • this pulls the eye straight
55
Q

what is the vestibular nystagmus?

A

nystagmus: slow movement in one moment, then a quick change to the opposite direction
- enables resetting of eye position during sustained head rotation

56
Q

what is the nystagmus experiment?

A
  • subject is seated and rotated towards the right at a constant rate in the dark
  • in slow phase, eyes rotate in the opposite direction to the head movement
  • in quick phase, rapid resetting movement back to the centre of the gaze

right quick phase movement = right beating nystagmus

Neuroscience (own deck) (14 decks)

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