Vestibular System Flashcards
What is the overall function of the Vestibular system
Posture and balance
Where is the vestibular system located
In the inner ear, embedded in the temporal bone
What is the vestibular system composed of
series of fluid filled membraneous tubes = labyrinths
What is the apparatus of the vestibular system
3 semi circular canals
Utricle
Saccule
What is the position of the semi circular canals
Are three dimensional due to being all right angled to each other
What is the swelling at the base of each semicircular canal called
Ampulla
Where is the utricle located
Swelling at the base of all the semicircular canals connecting them all
Where is the saccule located
The swelling underneath the base of the utricle
Where is sensory hair cells located in the vestibular apparatus
The ampulla of semicircular canals
Saccule
Utricle
What is the collective name of the utricle and the saccule
Otolith organs
What is the overall function of the otolith organs utricle
Detects linear acceleration and encode the position of the head in space
What is the overall function of the otolith organs saccule
detects vertical movement
What is the overall function of the semicircular canals
Detects rotational acceleration
Where are the sensory cells of the semicircular canals embedded
The ampulla
What is the sensory receptors called inside the ampulla
Cristae
What does the cristae consist of
A cupula - a flexible gelatinous strucutre
How is the crisate arranged in the ampulla
Stretches over the width of the ampulla
What is further embed in the cupula of the ampulla
Cilia of hair cells, which act as receptor cells
What is the purpose of the cilia of hair cells in the cristae
Synapse directly with the sensory neurones of the vestibular nerve
How is the cilla of hair cells receptors activated
By the movement of the endolmlyph in the semicircular canal pushing the gelatinous cupola of the cristae
What moves first when rotation of the skull occurs
The ampulla
Why doesn’t the endolymph move at first on rotation
As isn’t embedded in the skull
How does the hair cells in the Cupula detect rotational acceleration
Due to the inertia of the endolymph producing a drag which bends the cupula in the opposite direction of rotational movement and overall activates the cilla
What cause the endolymph to catch up the the rotational speed
Rotating at a constant velocity for several seconds
What is the affect of the endolymph catching up with the rotational speed
Endolymph now rotating at the same velocity so remove the sheering force, and cuppa no longer distorted
How does dizziness occur if you suddenly stop high velocity rotation
endolymph to continue to move due to momentum creating a continuing sense of movement
What is the two types of cilia hair cells
Kinocillium - single very large
Stereocillia - smaller series
What does distortion of the cilla in the direction of the Kinocillium cause
Depolarisation and increase discharge of the APs in the vestibular nerve
What does distortion of the cilia away from the Kinocillium lead to
Hyperpolorisation and decrease discharge of APs in the vestibular nerve
What does movement of the kinocillium allows the brain to determine
Movement in time and space
Why is the orientation of the cupula all slightly different
So the brain can build a 3D image of body position using the pattern of firing and inhibition received.
Where does the integration of the sensory information from vestibular apparatus take place
The cerebellum
When you stop rotating after rotating at constant velocity, what happens to the movement of endolymph and the cupola
The endolymph continue to move die to momentum
But the sheering of the cupula is in the opposite direction that at the start
What is the name of the sensory receptors in the otolith organs
Maculae
How is the Maculae orientated in the utricle
In the horizontal plane
How is the Maculae orientated in the saccule
In the vertical plane
What is the structure of the maculae
Set of cilla which embed into the gelatinous mass called the otolith membrane
What is embedded into the otolith membrane
CaCO3 crystals called otoliths.
What affect the positioning of otolith crystals
Gravitational forces
What doesn’t have much input on the positioning of the otolith crystals, why?
Endolymph
as otoliths have greater density
How do the macule in the utricle detect the tilting of you head
Tilting the head moves the otoliths and the otolith membrane in which they are embedded.
This distorts the jelly, and moves the cilia
What head tilt moves the otoliths in the direction of the kinocillium resulting in depolarisation
Backward tilt
What occurs when the head it tilted forward
Otoliths move in the opposing direction of the kinocillium resulting in hyperpolorisation decreasing AP discharge
What do the vertically orientated macule in the saccule respond to
Vertical forces e.g. movement in a lift
What provides information of the orientation of the head when lying down
The macula in the saccule
Where does the information to the brain via the vestibular nerve all originate from
The three cristae of the semicircular canals
and the two macule of the otolith organs
Where does many sensory afferents of the vestibule nerve terminate
In the vestibular centres in the medulla
How does the cerebellar centres associate with the vestibular centres
By co-ordinating the postural muscles required to maintain balance
Where does vestibular nuclei receive input from
Proprioceptors signalling limb and body position,
Neck,
Eye muscles
What is the vestibular nuclei
cranial nuclei for the vestibular nerve
Where is the vestibular nuclei found
grouped in both the pons and the medulla in the brainstem
How and where do the projections from the vestibular nuclei project
Project ipsilaterally, bilaterally and contra-laterally to descending motor pathways and the extra ocular nuclei/muscles
How does vestibular nuclei project to the cerebral cortex
Via the thalamus
What does the vestibular nuclei project to the cerebral cortex
perception of movement and body position = kinaesthesia.
Name three vestibular system reflexes
Tonic labyrinthine reflex
Dynamic righting reflex
Vestibulo-occular relflex
What does the vestibule system reflexs involve
Vestibulocortical and vestibulospinal tracts
What occurs in the tonic labyrinthine reflex
and how does it happen?
The axis of the head is kept in a constant relationship with the rest of the body.
Use information from maculae and neck proprioceptors
What occurs in the dynamic
righting reflex
and how does it happen?
Rapid postural adjustments that are made to stop you falling when you trip.
Long reflexes, involving extension of all limbs
How does vestibular apparatus have a strong connection to visual apparatus
Afferents from the semi-circular canals project and connect (within the vestibular nuclei) to afferent fibres travelling to the extraocular nuclei and thus have strong input to influencing eye movement.
What demonstrates the strong association between visual system and postural control
An increased difficulty experienced with balance when you close your eyes
How do people with vestibular apparatus destruction maintain good balance and how do they loose balance
Balance is good if movement is relatively slow and eyes are open
Balance is lost if they close their eyes
What is the two vestibulo-ocular reflex
Static reflex
Dyanmic vestibular nystagmus
What occurs in the static reflex
When you tilt your head, the eyes intort/extort to compensate, so that over a certain range, the image stays the right way up
What occurs in the dynamic vestibular nystagmus
series of saccadic eye movements that rotate the eye against the direction of rotation of the head and body so that the original direction of gaze is preserved despite head rotating
What occurs when the eyeball comes to the end of its range of movement
The extent of eye movement is restricted so it rapidly flicks back (nystagmus) to looking straight ahead
Define nystagmus
Rapid involuntary movement of the eye
If the head is rotating right what is the direction of the nystagmus
Right
In Post rotary nystagmus (at the end of rotation and nystagmus has occurred in the direction of the rotation)
Why then do you then get nystagmus in the opposing direction
As In the deceleration the endolymph is catching up and now pushing the cupula in the opposite direction
How in caloric stimulation when the ear is washed with either cold or warm fluid is the vestibular system stimulated
As fluid gets through the thin bones and sets up convection current affecting the endolymph
What is the affect of warm fluid >37C
Sets up nystagmus towards the affected side
What is the affect of cold fluid <37C
sets up nystagmus away from the affected side
What are the two tests that check vestibular function by investigating nystagmus s
Caloric stimualtion
(ear washed with water)
Post rotary nystagmus (rotated in a chair)
What is the symptoms experienced due to caloric stimulation
Nausea
Vomiting
Why is it good to test fro nystagmus
As shows if any lesions are present in the periphery to central vestibular pathways
Powerful maintained stimulation of the vestibular system can cause what
Kinetosis - motor sickness
Why does motion sickness/kinestosis occur in moving vehicles
Visual and vestibular system inputs to the cerebellum are in conflict
How does the cerebellum generate the symptoms of motion sickness
sends“sickness signal” to the hypothalamus to bring about the autonomic changes
What is the autonomic nervous symptoms caused by motion sickness
Nausea Vomiting decreased blood pressure Dizziness Sweating Pallor
= all equal autonomic
What symptoms does acute infection of vestibular apparatus - labyrinthitis
Autonomic Nervous system symptoms
Vertigo
what is the symptoms of Mieinieres disease
Vertigo
Nausea
Nystamgus
Tinnuitis
How does menieres disease affect vestibular function
as associated with overproduction of endolymph
What drugs is the inner ear sensitive towards
Streptomycin
How does a lesion of the brain stem affect vestibular function
Can cause nystagmus at rest
