Vestibular system Flashcards
Where does the vestibular system lie?
Deep within the temporal bone adjacent to the cochlea
What is the vestibule, where does it lie, what does it communicate with?
Central part of the bony labyrinth.
Communicates anteriorly with the cochlea and posteriorly with the semi-circular canals.
How is the vestibule separated from the middle ear?
Oval window
What are the three semi-circular canals?
Anterior, lateral and posterior
What lies inside the vestibule?
Saccule and utricle
Where does endolymph from the saccule and utricle drain?
Into the endolymphatic duct
Endolymph composition
High K+ content (like ICF)
Where do cell bodies of vestibular nerves lie?
Vestibular ganglia
Where do vestibular nerves project to?
Vestibular nuclei (medial, lateral, superior and inferior) and cerebellum
What are ampullae?
Swellings at the base of the semi-circular canal where sensory receptors lie
Where do ampullae stereocilia project?
Into gelatinous cupula
What movements do semi-circular canals respond to?
Rotation and angular acceleration
What happens in the ampullae upon angular acceleration?
Endolymph lags behind the head due to the inertia of the fluid, this flexes the cupula and bends the cilia
What happens when hair cells bend towards the kinocilium?
Hair cell depolarises and leads to increased glutamate release onto CNVIII which generates a train of action potentials in the vestibular nerve
What happens when the hair cells bend away from the kinocilium?
Hair cells hyperpolarize leading to inhibition of transmitter release.
Does hair cells stimulation cause discharge?
No, only increase/decrease discharge rate compared to tonic resting position.
What happens inside the semi-circular canals in rotation?
Displacement of the fluid in the horizontal canal -activating the vestibular system on one side (rapid firing increase), whilst inhibiting it on the other side.
How long does the vestibular response to head rotation in one direction last and why?
Happens immediately but ceases after several seconds (about 6 secs) (falling to zero) even when the head is still rotating - this is because the fluid starts to rotate as well, hair bundle is no longer deflected.
What happens inside the semi-circular canals when the head stops rotating?
Endolymph continues to move around, we perceive this as the opposite, causing an imbibition of the stereocilia
What are the axes that the semi-circular canals detect?
Pitch (y-axis nodding yes), roll (x-axis shoulder to shoulder), yaw (z-axis shaking no)
Each semicircular canal (anterior, posterior or horizontal) responds maximally to
A rotation about an axis perpendicular to its plane.
Fibres from the horizontal and anterior canals primarily synapse in the
Superior, lateral and medial nuclei
Fibres from the posterior canals primarily synapse in the
Superior, descending (inferior) and medial nuclei
In the saccule and utricle what do the hair cells project into?
Gelatinous otolithic membrane and is overlaid by otoconia/otoliths
What is the otolithic membrane covered by (saccule and utricle)?
Otoconia/otoliths
What are otoconia/otoliths?
Calcium carbonate crystals that have inertia.
What are type I hair cells?
Surrounded by an afferent calyx
What are type II hair cells
More efferents that synapse directly on the hair cell body (punctate boutons)
How is the saccule/utricle membrane divided?
Central striola, on either side there is a division of hair cell type
What does the saccule detect?
Vertical linear acceleration
What does the utricle detect?
Horizontal linear acceleration
Why are hair cells arranged in the way they are in the saccule and utricle?
So they can detect changes in motion in any direction
What responds to gravity?
Saccule and utricle
Afferents from the utricle and saccule terminate mainly in the
Inferior and medial nucleus. Lateral nuclei receive synapses from saccule and utricle too.
Vertigo
Inputs from vestibular system do not match environment
How does the cerebellum influence the VOR?
Visual feedback that can detect errors in the VOR is too slow to correct the very rapid responses generated by the VOR during a head movement.
These adaptive changes are lost following a lesion of the cerebellar flocculus.
The vestibular part of the cerebellum is the
Flocculus and nodulus
Benign paroxysmal positional vertigo (BPPV)
Pieces of otolithic membrane break off and fall into semi-circular canal displacing fluid. Common in elderly.
Meniere’s disease
Improper drainage of endolymph via endolymphatic duct.
Gentamycin can be used to kill hair cells in severe cases.
Vestibular nystagmus
VOR rapid eye movement and slow movement to reset eye gaze
Vestibular nystagmus is normal when a person is being rotated.
Egocentric coordinate system.
Relative position of parts of body with respect to each other
Exocentric coordinate system.
Relative position of body with respect to environment
Geocentric coordinate system.
Orientation of body in gravitational field
Vestibulocollic reflex
Neural reflex that activates neck muscles when head motion is sensed by the vestibular organs in the inner ear
Mediated by the medial vestibulospinal tract
The semi-circular canals lie within the…
Petrous part of the temporal bone
The semi-circular canals are concerned with…
Angular acceleration
The nerves innervating the utricle and saccule arise in the…
Vestibular ganglion
The vestibular nuclei have strong interconnections with the…
Oculomotor nuclei
The major target of the output from the vestibular part of the cerebellar cortex is the..
Fastigeal nucleus
