Vestibular system Flashcards
True or false: the vestibular system does not have a dedicated primary area in the brain.
True.
With what liquid are the vestibular chambers filled with?
Endolymph.
What are the vestibular structures responsible for processing head tilts and linear acceleration? The vestibular structures responsible for processing rotations of the head?
Head tilts and linear acceleration:
- Utricle
- Saccule
Rotations of the head:
- Anterior semicircular canal
- Posterior semicircular canal
- Lateral semicircular canal
What is the sensory receptor of the vestibular system?
The hair cells.
Where are located the hair cells in the vestibular system?
At the base of SC canals, in the ampullae.
In the utricle and saccule.
What is anatomically common for the ascending information of the auditory system and the vestibular system?
Vestibular nerve and cochlear nerve travel together as distinct divisions of the CN VIII.
Is the potential of hair cells in vestibular system biphasic or tonic?
Biphasic, like hair cells in the cochlea (intrinsic to its structure).
What are the hair cells polarities (orientations) in the different structures of the vestibular system?
Ampullae: single polarity
Saccule: bipolarity pointing outward
Utricle: bipolarity pointing inward
Where are found the otolith organs? What is their role? List three elements of their structure.
Located in:
-Utricle and saccule
Role:
-Provide sensibility to gravity (for head tilts and translational movements)
Structure:
- Hair cells in otolith organs are contained in a sensory epithelium patch called maccula
- Gelatinous layer sits on top of the maccula, the otolith membrane
- On gelatinous layer sits otoconia, little crystals pulled by gravity
In the utricle and the saccule, what is the consequence of hair cells pointing either inward or outward on both sides of the striola?
Movement in one direction inhibits the population of hair cells on a side of the striola and excites the population of hair cells on the other side.
The saccules are oriented ____, responding to ____ head movements. The utricles are oriented ____, responding to ____ head movements.
Words to place:
vertical
horizontally
vertically
horizontal
The saccules are oriented vertically, responding to vertical head movements. The utricles are oriented horizontally, responding to horizontal head movements.
Concerning the firing rate, what distinguishes hair cells in the vestibular system to hair cells in the auditory system?
Vestibular hair cells have a resting firing rate, whereas cochlear hair cells don’t have one.
How many ampullae are there in total in one set of SC canals?
3
True or false: ampullae working together as a pair depolarize and hyperpolarize together.
False: depolarization in one ampulla results in hyperpolarization is the opposite corresponding ampulla.
What are the three pairs of SC canals? For what axis each is responsible for?
L-horizontal and R-horizontal : horizontal plane
L-anterior and R-posterior : LARP plane
R-anterior and L-posterior : RALP plane
Name two differences about the vestibular system compared to the other sensory modalities.
- Multisensory (visual and somatosensory pathways)
- Has a motor function
What is the obligatory passage in the central pathways of the vestibular system?
Vestibular nuclei (pons).
What are the four pathways diverging from the vestibular nuclei?
- Vestibuloocular pathway
- Descending projections to spinal cord
- Vestibulo-cerebellar pathway
- Thalamus to cortex
What is the role of the vestibuloocular pathway?
Generating eye movement reflexes to counter head movements so gaze can be fixated.
Where are located the nuclei responsible for eye movements?
Brainstem.
True or false: when fixating in a gaze, eye movements will go in the opposite direction of head movements.
True.
What can arise from damage to VOR?
Oscillopsia.
What can be used to assess the integrity of vestibular system?
Doll’s eye maneuver.
What is the role of the descending projections to spinal cord from vestibular nuclei?
Guide postural adjustments of head and body.
The descending projections to spinal cord from vestibular nuclei form two reflexes, what are they?
Vestibulocervical reflex and vestibulospinal reflex.
What does indicate the few number of synapses between the vestibular nerves and the motor neurons?
Very fast pathway.
What are the respective pathways of the vestibulocerebral and vestibulospinal reflexes? What are their respective roles?
Vestibulocerebral reflex pathway: SC canals ->medial vestibular nucleus ->medial longitudinal fasciculus -> upper cervical levels of spinal cord.
Vestibulocerebral reflex role: regulation of head position.
Vestibulospinal reflex pathway: otolith organs -> lateral vestibular nucleus -> lateral vestibulospinal tract ->ventral horn of spinal cord.
Vestibulospinal reflex role: mediation of balance and upright posture.
What is the principle target of the vestibular portion of the vestibulocochlear nerve?
Cerebellum.
From where are most descending projections for vestibular central pathways coming from?
Cerebellum.
What is the main purpose of bidirectional vestibulo-cerebellar circuits?
Allow to modulate vestibular activity.
What are the main roles of the cerebellum in its vestibular functions? What are the main structures responsible for each role?
- Bring adaptive changes to VOR -> flocculus and paraflocculus (purkinje cells of the cerebellum modulating firing properties of vestibular system)
- Distinguishing head tilts from translational movements ->nodulus and uvula (integrate information from otolith organs and SC canals)
- Distinguishing passive movements from self generated movements ->rostral fastigial nucleus (receives inputs from cortex)
Describe the vestibular pathway to the cortex.
Superior and lateral vestibular nuclei →ventral posterior nuclear complex of thalamus → cortex area 2v, cortex area 3a and parietoinsular vestibular cortex
What is the role of each structure innervated by axons coming from the ventral posterior nuclear complex of the thalamus in the cortex?
- Cortex area 2v: part of dorsal visual stream →help to localize head in space
- Cortex area 3a: part of somatosensory cortex →integrate with proprioceptive information
- Parietoinsular vestibular cortex: integrate head motion
True or false: axons from CN VIII eventually project to primary vestibular cortex.
False, no such cortex exists.
