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PHYS - NEURO > 9. AUDITORY & VESTIBULAR SYSTEM > Flashcards

9. AUDITORY & VESTIBULAR SYSTEM Flashcards

1
Q

Describe the structure of a hair cell

A
  • Hair cells can act as water motion, gravity or sound detectors
  • Stereocilia are found on top of the hair cell
  • An extracellular matrix surrounds the hair cell & protects it known as the tectorial membrane
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2
Q

What do hair bundles consist of?

A
  • Actin

- Stiff rods

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3
Q

What’s the extracellular matrix for hair cells?

A
  • tectorial membrane
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4
Q

What’s the extracellular matrix for the macula?

A
  • otoconial membrane is found in the macula of the vestibular system
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5
Q

How are sterocilia arranged?

A
  • Stereocilia are arranged in bundles
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6
Q

What two structures link the sterocilia?

A
  1. Connectors - link the stereocilia laterally

2. Tip links - found at the top of the stereocilia

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7
Q

What are the three types of connectors?

A
  1. Top connectors
  2. Shaft connectors
  3. Ankle links
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8
Q

How does current flow through the stereocilia in response to motion?

A
  • When the hair bundle moves in one direction, there’s pull or stretch at the tip links
  • This distorts the tip links mechanically
  • tip links are associated with ion channels, so distortion of the stereocilia causes ion channels to open or close
  • The movement of the hair bundle determines if depolarisation or hyperpolarization occurs
  • This allows current to flow through the stereocilia
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9
Q

In what direction does the hair bundle move for depolarisation?

A
  • Towards the tallest stereocilia
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10
Q

In what direction does the hair bundle move for hyperpolarisation?

A
  • Away from the tallest stereocilia
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11
Q

Describe the process by which depolarisation & neurotransmitter release occurs in the tip links

A
  1. Tip links are associated with ion channels, so distortion of the tip links causes ion channel opening
  2. The stereocilia are surrounded by endolymph which is high in K+
  3. The K+ influx causes depolarisation
  4. VGCC open due to depolarisation
  5. Ca2+ results in neurotransmitter release
  6. Current flows proportionately
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12
Q

What cells detect water motion in hair cells?

A
  • Neuromasts or Mechanoreceptors can detect the flow of water including the velocity & direction
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13
Q

What is the cupula?

A
  • A gelatinous extracellular matrix surrounding the hair cells to prevent direct contact with water
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14
Q

How does the cupula help to detect water motion?

A
  • As water flows in the lateral line system (fish), the cupula will move in the opposite direction of water flow to protect the hair cells
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15
Q

What does the vestibular system detect?

A
  1. Motion
  2. Head position
  3. Spatial orientation
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16
Q

What are the three regions of the ear?

A
  1. OUTER EAR
  2. MIDDLE EAR
  3. INNER EAR
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17
Q

What two structures make the inner ear?

A
  1. Semi-circular canals - vestibular system

2. Cochlea - auditory system

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18
Q

What are the three semi-circular canals?

A
  1. Posterior semi-circular canal
  2. Anterior semi-circular canal
  3. Horizontal posterior canal
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19
Q

What type of motion does the posterior semi-circular canal detect?

A
  • Roll - shoulder to shoulder movement
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20
Q

What type of motion does the anterior semi-circular canal detect?

A
  • Pitch - forwards & backwards movement
21
Q

What type of motion does the horizontal semi-circular canal detect?

A
  • Yaw - side to side movement
22
Q

What are the cilia of the semi-circular canals attached to?

A
  • Gelatinous cupula
23
Q

Describe motion detection in the semi-circular canals

A
  • The semi-circular canals are filled with endolymph, the endolymph moves in the opposite direction to head rotation
  • Head rotation causes fluid motion in the semi-circular canals
  • However, the fluid motion in the semi-circular canals lags due to inertia. This pulls the cupula in the opposite direction to head movement
  • The cilia are displaced causing depolarisation
24
Q

What are the otolith organs?

A
  • The otolith organs are part of the vestibular system
  • The otolith organs detect linear acceleration (forwards & backwards and gravitational forces)
  • Utricle & Saccule or Utricular macular & Saccular macular
  • Detect different directions due to arrangement of hair cells
25
Q

What does the utricular macular detect?

A
  • Right & left

- Horizontal

26
Q

What does the saccular macular detect?

A
  • Forwards & backwards
27
Q

Describe motion detection in the otolith organs

A
  • The hair cells of the otolith organs are surrounded by a layer of otoconia crystals
  • Upon linear acceleration (movement), the otoconia crystals are displaced, deflecting the cilia
  • The movement of the otoconia crystals in response to motion, results in deflection of the stereocilia beneath
  • The stereocilia are located in the otolithic membrane
28
Q

What is rarefaction & compression?

A
  • Compression = high pressure, molecules close together

- Rarefaction = low pressure, molecules spread out

29
Q

What determines the wavelength & frequency of a sound wave?

A
  • The rate at which rarefaction & compression occurs determines the wavelength
  • The rate at which the pressure cycles between rarefaction & compression determines frequency
30
Q

What is the pathway of sound waves to the auditory cortex?

A
  1. Changes in air pressure detected as sound eaves
  2. Causes motion in the cochlea
  3. Electrical activity conduction to cochelar nucleus
  4. Cochlear nucleus -> Olivary complex -> lateral lemniscus -> inferior colliculus -> medial geniculate body -> auditory complex
31
Q

What is the pinna & what does it do?

A
  • The pinna is found in the outer ear
  • It gathers sound from the environment and passes it on to the eardrum
  • Made entirely of cartilage & covered with skin
32
Q

What is microtia?

A
  • Malformation of the external part of the ear (pinna)

- Varies in severity (Grade I - 4)

33
Q

What is Grade 1 microtia?

A
  • Less than complete development of external ear

- identifiable structures and a small but present ear canal

34
Q

What is Grade 2 microtia?

A
  • Partially developed ear

- closed stenotic external ear canal producing conductive hearing loss

35
Q

What is Grade 3 microtia?

A
  • Absence of the external ear
  • small peanut like vestige structure
  • absence of external ear canal and drum
36
Q

What is Grade 4 microtia?

A
  • absence of total ear/ anotia
37
Q

What is otitis media/glue ear?

A
  • Collection of fluid in the middle ear which impedes the movement of the ossicles
  • Loss of amplification as eardrum is pushing against the fluid
38
Q

What structures make up the middle ear?

A
  • Tympanic membrane
  • Ossicles
  • Oval window
39
Q

What is the tympanic membrane?

A
  • The tympanic membrane is the eardrum, it is connected to the ossicles
  • Arriva of a sound wave causes vibration of the tympmanic membrane, separating the middle ear from the inner ear
40
Q

What are the ossicles?

A
  • Ossicles = trio of tiny bones on the other side of the tympanic membrane
  • Vibration is passed on to ossicles form tympanic membrane which then conducts it to oval window of the cochlear
  • Smallest bones of the body
41
Q

What is the cochlea?

A
  • Cochlea is found in the inner ear
  • It consists of fluid filled canals that run parallel to each other.
  • The cochlea is divided by a flexible basilar membrane
42
Q

What are the three chambers of the cochlea?

A
  1. Scala vestibuli
  2. Scala media
  3. Scala tympani
43
Q

Where is the basilar membrane & it’s function?

A
  • It’s between the scala tympanis and the scala media of the cochlear
  • Basilar membrane filters sound according to frequency
44
Q

What does the stapes do?

A
  • Stapes causes compression of fluid within cochlea
45
Q

What is the organ of corti?

A
  • Movement of the basilar membrane is converted into electrical activity in the organ of corti
  • Organ of corti lies on top of cochlear membrane
46
Q

Describe how the movement of the basilar membrane is converted into electrical activity?

A
  • Inner & outer hair cells are attached to the organ of corti
  • Motion of the basilar membrane causes displacement of the stereocilia (hair cells) on the Organ of Corti
  • Displacement of the cilia leads to depolarisation which causes the outer hair cell to touch the tectorial membrane
47
Q

What’s the function of an inner hair cell?

A

Inner hair cells have afferent synapses which take information away from the hair, towards the CNS

  • Movement of the tectorial membrane causes inner cell to move which causes depolarisation
  • There’s an influx of K+ from the endolymph
  • A smaller influx results in a lower inner hair cell output
48
Q

What’s the function of an outer hair cell?

A
  • Outer hair cells have efferent synapses meaning they receive information
  • They are involved in cochlear amplification
49
Q

Describe the process of cochlear amplification?

A
  1. Outer hair cells are motile, upon displacement there’s depolarisation
  2. The influx of positive ions causes the outer hair cell to contract & shrink, contracting the tectorial membrane
  3. Basilar membrane is pulled inwards towards the basilar which causes inner hair cell to move
  4. K+ influx results in inner hair cell output to CNS

PHYS - NEURO (18 decks)

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