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231 > Lecture 23: The Vestibular System > Flashcards

Lecture 23: The Vestibular System Flashcards

1
Q

What is the vestibular system concerned with?

A

the sensation of balance

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2
Q

What are the stimuli of the vestibular system?

A

angular and linear accelerations of the head

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3
Q

What is linear acceleration? Give two examples

A

This is horizontal and vertical accelerations of our body but our head is moving in respect to gravity.
Examples are going in an elevator or traveling in a car

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4
Q

What is angular acceleration? give examples

A

this is rotation of the head when you nod, shake or tilt your head

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5
Q

What is the role of the vestibular system?

  • it generates ______ to compensate for head __________ and the perception of __________ in space
  • the system provides information to help with _______ of right _______
  • it also provides __________ for conscious awareness of p__________/m____________/a_________ of the head and body
A
  • it generates reflexes to compensate for head movement and the perception of movement in space
  • the system provides information to help with maintenance of right posture
  • it also provides information for conscious awareness of position/movement/acceleration of the head and body
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6
Q

What is responsible for the vestibular system?

A

the vestibular apparatus

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7
Q

What is the vestibular apparatus?

A

it is membranous filled tube

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8
Q

How many parts are there in the vestibular apparatus? What are these called?

A

2 parts

  • the semicircular canals
  • the otolith organs
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9
Q

Where is the vestibular appartus?

A

it is part of the inner ear but it is concerned with balance and spacial orientation of the head and body, not with sound

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10
Q

How many semicircular canals are there and what are their names?

A

there are 3 of them:

  1. the anterior semicircular canal
  2. the posterior semicircular canal
  3. the horizontal semicircular canal
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11
Q

How many otolith organs are there and what are they called?

A

there are two of them:

  1. uricle
  2. saccule
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12
Q

What are the semicircular canals sensitive to?

A

to angular acceleration during head rotation

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13
Q

The semicircular canals are aligned in how many axes?

A

3

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14
Q

Each of the semicircular canals is most stimulated by what?

A

acceleration in its preferred plane

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15
Q

What are the semicircular canals filled with?

A

endolymph

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16
Q

Does the endolymph have high K+ or low K+ concentration and high Na+ or low Na+ concentration?

A

it is like intracellular fluid so it has a high K+ concentration and low Na+

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17
Q

The horizontal semicircular canal is stimulated by what? Give an example

A

stimulated by acceleration in the transverse plane

eg. looking both ways when crossing the road

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18
Q

The anterior semicircular canal is stimulated by what? Give an example

A

stimulated by acceleration along the sagittal plane

eg. nodding your head

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19
Q

The posterior semicircular canal is stimulated by what? Give an example

A

stimulated by acceleration along the coronal plane

eg. trying to crack your neck

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20
Q

What is the bulbous end of the semicircular canal called?

A

the ampulla

21
Q

Describe the ampulla?

A

there are hair cells that project cilia into the lumen of the ampulla

22
Q

Where do the hair cells sit inside the ampulla?

A

inside a gelatinous blob called the cupula

23
Q

What is the purpose of the cupula in the ampulla?

A

It blocks the lumen so the fluid in the semicircular canal can’t move

24
Q

Describe the role of the ampulla when there is a head movement to the right

A

Fluid inside the ampulla has inertia which means that the movement of the fluid goes towards the right. This puts pressure on the cupula so it bends and so the hair cells bend too

25
Q

Define inertia

A

It is the resistance of an object to a change in its velocity

26
Q

How many direction can the ampulla detect? Why?

A

2 direction because the cupula can bend in 2 directions

27
Q

How can the brain detect between the bending of the cupula to the left or right?

A

The vestibular nerve has a resting discharge rate so when we are standing upright, the vestibular system is constantly firing. However, when we move and get acceleration of the head, the cupula and hair cells bend. If there is bending towards the longest cilia, there is opening of mechanically gated ion channels and K+ enters. This depolarises the hair cells so there is opening of voltage gated Ca2+ channels, there is a Ca2+ influx which causes the release of neurotransmitter onto afferent nerve fibres onto the vestibular nerve. This means there is an increase in firing from the vestibular nerve.
If there is bending towards the shortest cilia, the mechanical gated channels close so no K+ can enter. The hair cells are hyperpolarised so the Ca2+ channels don’t open, there is no Ca2+ influx so no neurotransmitter is released so there is a reduction of the firing of the vestibular nerve

28
Q

What does a resting discharge rate mean for the vestibular hair cells?

A

it means these vestibular hair cells detect movement in 2 directions

29
Q

Describe the steps when there is bending of cilia towards the longest cilia

A
  • bending of cilia towards the longest cilia
  • opening of mechanically gated ion channels
  • K+ influx and depolarisation of hair cell
  • opening of voltage gated Ca2+ channels and Ca2_ influx
  • release of neurotransmitter, increased firing rate
30
Q

Describe the steps when there is bending of cilia towards the shortest cilia

A
  • bending of cilia towards the shortest cilia
  • closing of mechanically-gated ion channels
  • hyperpolarisation
  • closing of voltage-gated Ca2+ channels
  • no neurotransmitter release, decreased firing rate
31
Q

Hair cells are embedded in the cupula BECAUSE semi-circular canals need to detect linear acceleration in two directions

A

the first statement if true but the second statement is false
the second statement is false because the semicircular canals detect angular acceleration not linear acceleration

32
Q

What do the otolith organs do?

A

these detect linear acceleration - the movement of the head in relation to gravity

33
Q

Describe the position of the utricle when we are standing upright

A

it is horizontal when we are standing upright so the hair cells and cilia are projecting up vertically

34
Q

What does the utricle detect?

A

it detects horizontal linear acceleration because this is what will cause the bending of the hair cells and cilia

35
Q

Describe the position of the saccule when we are standing upright

A

it is vertical when we are standing up so the hair cells are cilia are projecting up horizontally

36
Q

What does the saccule detect?

A

it detects vertical linear acceleration because this is what will cause the bending of the hair cells and cilia

37
Q

Describe the structure of the otolith organs

A

The hair cells sit in an epithelial layer called the macula, the hair cells project into the lumen. On top of these there is the otoconia which act as a weight eg. so when we move our head to the right, due to the inertia of the otoconia, the otoconia don’ move as fast so it puts pressure down onto the hair cells which cause the hair cells to deflect

38
Q

What is the otoconia?

A

stores of CaCO3

39
Q

Is the transduction pathway the same for the otolith organs are the semicircular canals?

A

yes

40
Q

Describe the central pathways associated with the vestibular system

Axons project to the ______ nuclei and the project to the medial __________ fasciculus to the ___________ nerves. This information is sent to the muscles in the ________ to move our _______ and stabilise them. It is also sent to _______ _________ in our head and neck to ______ them, and to the ________ to maintain balance

A

Axons project to the vestibular nuclei then project to the medial longitudinal fasciculus to the oculomotor nerves. This information is sent to the muscles in the eyes to move our eyes and stabilise them. It is also sent to motor neurons in our head and neck to stabilise them, and to the cerebellum to maintain balance

41
Q

List 4 vestibular disorders

A
  • vertigo
  • motion sickness
  • bedspins
  • acoustic neuroma
42
Q

Describe vertigo

A

This is caused by a disease affecting the vestibule or its afferent fibres. It can cause the illusion of movement, and dizziness

43
Q

Describe motion sickness

A

This is caused by a mismatch between visual and vestibular information

44
Q

Describe bedspins

A

This is caused by alcohol because ethanol infiltrates the cupula. This lowers its density because alcohol is less dense than water which causes the cupula to float, the bending of cilia of hair cells creates the perception of movement

45
Q

Describe acoustic neuroma

A

This is a tumour caused by abnormal growth of schwann cells which puts pressure on the vestibulocochear nerve so there is impaired transmission

46
Q

What is the effect of ototoxic drugs?

A

Antibiotics are the worst examples of ototoxic drugs because they damage the hair cells and can result in temporary or permanent hearing loss and disorders of balance

47
Q

The vestibular system can detect movement in two directions BECAUSE the vestibular nerve has a resting discharge rate

A

both answers are correct and are causally related

48
Q

In sound transduction, what results in a displacement of the basilar membrane?

A

a change in the fluid pressure of the scala vestibuli

231 (41 decks)

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