Vestibular Function Flashcards
What is the vestibular system about?
Balance and posture
Where is the vestibular system found?
Inner ear
What is the vestibular system made up of?
Fluid filled labyrinths which are embedded in the temporal bone
Which organ is the organ of hearing?
Cochlea
Which nerve sends sensory information from the ear to the brain?
Vestibular nerves, part of vestibulocochlear nerve (CN VIII)
What does the vestibular apparatus consist of?
3 semi-circular canals
Utricle
Saccule
What is the name given to the swelling at the base of the semi-circular canals?
Ampulla
What do the ampulla contain?
Sensory hair cells
What are the otolith organs?
Utricle and saccule
What does the utricle detect?
Back/front tilt of the head
Horizontal acceleration (as if you were in a car)
What does the saccule detect?
Vertical acceleration (as if you were in a lift).
What do the ampulla of the semi-circular canals detect?
Rotational acceleration (e.g. turning head quickly).
-?maybe remember this due to the fact they’re round and it’s rotational acceleration?
Where are the hair cells in the ampulla of the semi-circular canals embedded in?
Flexible gelatinous structure called the cupula
What does the cupula become distorted with?
Movement of endolymph within the canal
What happens when the cupula is distored?
Distorts the hair cells
What does distorting the hair cells of the cupula do?
Sets up an action potential in the vestibular nerve
How does the semi-circular canals detect rotational acceleration?
If rotating the skull to the left or right, the endolymph in semi-circular canals does not initially move as has a degree of inertia.
However, the ampulla moves instantly as is embedded in the skull.
Describe how dizziness occurs.
This might be a long one but it makes sense!!
If rotating at a constant velocity, the endolymph catches up and rotates at the same speed.
These can take several seconds but stops the shearing process, which drags the cupula through the endolymph.
However, when you stop spinning, the endolymph continues to move due to the momentum, creating a continuing sense of movement, causing dizziness.
Name the two types of cilia in hair cells.
Kinocilium
Stereocilia
Which is larger- kinocilium or stereocilia?
Kinocilium
What would happen if there was distortion of the cilia in the direction of the kinocilia?
Depolarisation would occur and would be increased firing of action potentials in the vestibular nerve
What would happen if there was distortion of the cilia in the direction away from the kinocilia?
Hyperpolarisation leading to decreased discharge on action potentials in the vestibular nerve
Which part of the brain controls balance?
Cerebellum
What is the name given to the sensory apparatus in the utricle and saccule?
Maculae
Which plane of the utricle are the maculae orientated on?
Horizontal plane
(detect horizontal acceleration)
Which plane of the saccule are the maculae orientated on?
Vertical plane
(detect vertical acceleration)
The maculae, like the ampulla, have a set of cilia. What makes up this set of cilia?
One kinocilium and several stereocilia.
What is embedded in the otolith membrane?
Calcium carbonate crystals
What is the name given to the calcium carbonate crystals in the otolith membrane?
Otoliths
A man tilts his head.
What detects this change?
Macula in the utricle
(horizontal plane).
What happens to the otoliths when the head is moved?
Moves along with the otolith membrane
A women goes into a lift. Which part of the vestibular system relays this information to the brain?
Vertical macula in saccule
Kinesthesia?
Awareness of body position
What does the tonic labyrinthine reflex do?
Keeps the axis of the head in a constant relationship with the rest of the body.
What does the tonic labyrinthine reflex use information from?
Uses information from the maculae and neck proprioceptors.
What does the dynamic righting reflex do?
Makes rapid postural adjustments that are made to stop you falling when you trip.
In the vestibulo-cular reflexes, what is there strong association between?
Vestibular apparatus
Visual apparatus
Postural control
What is meant by vestibular nystagmus?
Predictable eye movement in response to stimulation from the vestibular system.
What happens in vestibule-ocular reflex?
Series of saccadic eye movements which rotate the eye against the direction of passive rotation of the head and body.
This means the original direction of gaze is persevered despite the head rotating.
Like you’re on a roundabout and you fix on a certain point until you can no longer see it.
What is a nystagmus?
The rapid flick back movement of the eye
If the rotation experienced is right, what direction will the nystagmus be?
Right
You can use nystagmus to test vestibular function clinically. Name one the most common ways to test it.
Caloric stimulation
Describe what happens in caloric stimulation.
-Outer ear is irrigated with a fluid warmer or colder than body temperature.
-This warms or cools the endolymph, causing it to behave in a different way.
-There will be a nystagmus.
If during the caloric stimulation, you use fluid cooler than body temperature, what will the nystagmus be like?
Nystagmus away from the affected side
If during the caloric stimulation, you use fluid warmer than body temperature, what will the nystagmus be like?
Nystagmus towards affected side
-> Remembers COWS
Cold=opposite
Warm=same
Why is it important when getting ear wax irrigation that the fluid is at 37 degrees?
Prevents a nystagmus
What can nystagmus cause for the patient?
Dizziness
When may nystagmus take place?
Seen in patients with lesions in their CNS or PNS
Kinetosis?
Motion sickness
When is motion sickness most likely to occur?
When the visual and vestibular system inputs to the cerebellum are in conflict
Why may someone get car sick?
Vestibular system is telling brain you are moving, visual system is telling brain you’re not
Which symptoms are felt in motion sickness?
Nausea
Vomiting
Decreased BP
Dizziness
Sweating
What is labyrinthitis?
Infection leading to interference with normal vestibular function.
What symptoms are present in those with labyrinthitis?
All ANS symptoms present with motion sickness e.g. nausea, vomiting, decreased BP, dizziness
AND
Vertigo
What is vertigo?
The perception of movement in the absence of movement
What is Meniere’s disease?
A bit like labyrinthitis but no infection involved.
Associated with the overproduction of endolymph causing increase pressure.
List some symptoms seen in those with Meniere’s disease.
Vertigo
Nausea
Nystagmus
Tinnitus
