Vestibular system Flashcards
Sensory purpose of
vestibular system
- perception of motion and orientation
- angular acceleration
- linear acceleration: up and down or left and right
- position in relation to gravity
motor purpose of
vestibular system
- control of eye movement to permit clear visual image of surrounds
- maintenance of equilibrium and desired posture
Vestibular structures: periphery
- ear
- vestibular apparatus: vestibular receptors and cranial nerve axons
vestibular strucutres: CNS
- Vestibular nuclei in brainstem
- cerebral cortex (vestibular cortex)
Describe how information travels
- sensory information from ear converted into neural signals
- vestibular nerve => vestibular nuclei (w/i) brainstem)
Vestibular nuceli projections provide
- sensory input about head movement and position
- gaze stabilization
- postural adjustments autonmic function and consciousness
how do the canals detect movement of the head
- detect angular acceleration of the head (change while it’s happening)
- beginning of rotation; endolymph stays behind
- rotation maintained; endolymph catches up
- rotation stops; endolymph keeps going
hair cell firing
- head stationary = baseline rate
- head begins to turn: inertia causes fluid in canal to lag behind; deflects cupula, bends cilia
- hair bending: changes baseline rate hair cells firing - determining frequency of signals sent to the vestibular nerve
Describe cupula deflection
- head movement in one direction
- fluid in canal moves the other
what are the functional pairs of the canals
- both horizontal
- right anterior loop and left posterior loop
- left anterior loop and right posterior loop
What do the functional pairs do
- maxium fluid flow in each SCC: occurs during movement in a single plane
- max flow in pairs prevents stimulation of other canals
- reciprocal signals: one increases and one decreases
Non-reciprocal signals
if signals from pain are not reciprocal
- postural control abnormalities
- abnormal eye movement = nystagmus
- nausea
Otolith organs
- utricle and saccule comprise medial portion of the vestibule
- each organ contains sensory hair cells embeded within a membrane with otoconia attached to the medial wall of saccule and floor of utricle
- specific gravity of otoconia is greater than the surrounding endolymph
- responsive to linear acceleration forces, example: gravity
Macula
- receptor inside the utricle and saccule
- hairs projecting are embedded in a gelatinous material.
- Atop the gelatinous material are otoliths, which are small, heavy, sandlike crystals.
- When the macula is moved into different positions, the weight of the otoliths bends the hairs, stimulating the hair cells and changing the pattern of vestibular neuron firing.
How do the otolith crystal change with age
- Increased variability in size
- Hypertrophy
- Fragmentation
- Fissured
- Pitted
- Weakening of linkages
vestibular system
Vascular supply
- Originates from the basilar artery (posterior circulation)
Primary supply for the vestibule is as follows:
- Basilar → AICA → Labyrinthine artery → Anterior vestibular artery—supplies anterior and horizontal semicircular canals and the utricle
- Basilar → AICA → Labyrinthine → common cochlear → posterior vestibular artery - supplies posterior canal and saccule
Neural innervation
- superior portion of VII nerve innervates anterior and horizontal canals and utricle
- Inferior portion of VIIIth nerve innervates posterior canal and saccule
what is the vestibular nerve made of
- Vestibular nerve made up of bipolar neurons of vestibular ganglion
- Distal axon
- Vestibular nerve
- Proximal axon
- CN VIII
whats included in the central vestibular system
- four vestibular nuclei
- six pathways
- vestibulocerebellum
- vestibular cortex
What are the vestibular nuclei
- Superior
- lateral
- medial
- inferior
- most output via cranial nerve VIII to vestibular nuclei in the medulla
- some fibers project directly to cerebellum
Vestibulocerebellum
- projects to cerebellum
- inputs from vestibular apparatus
- to eye influence eye movements, vestibular nuclei, balance and equilibrium
What are the 6 pathways in the central vestibular system
- pathways that convey information from vestibular nuclei
- medial longitudinal fasciculus
- vestibulospinal tracts
- vestibulocollic
- vestibulothalamocortical
- vestibulocerebellar
- vestibuloreticular
Medial longitudinal fasciculus (MLF)
- helps VOR
- to extraocular nuclei and superior colliculus
- influences eye and head movements
Vestibulospinal tracts
- to LMNs
- influence posture
Vestibulocollic
- to nucleus of accessory nerve
- influences head position
Vestibulothalamocortical
- conscious awareness of head position and movement
Vestibulocerebellar
- to vestibulocerebellum
- controls magnitude of muscle responses to vestibular info
- including VOR
vestibuloreticular
pathway
- to reticular formation
- autonmoic centers for nausea/vomiting
- center of brainstem
Vestibular system function
motor control
- gaze stabilization: VOR
- postural adjustments
motor control
postural adjustments for vestibular system
how does it work
reciprocal connections between vestibular nuclei and
- spinal cord
- reticular formation
- superior colliculus
- CN XI nucleus
- cerebellum
even when someone is a coma the eye will follow if they dont = brain dead
Vestibulocortex
- parietal insula
- lesion = change in awareness of head position and head movement and perception of vertical
Vestibular reflexes
the types
- VOR: vestibulo-ocular reflex
- VSR: vestibulospinal reflexes stabilizes head and body
VOR
what does it do
- produces eye movements of same velocity as head movement
- opposite direction
Vestibulospinal reflexes for postural adjustments
- reciprocal connections between vestibular nuclei and
- spinal cord
- reticular formation
- superior colliculus
- cerebellum
descending tracts with vestibular system
- lateral vestibulospinal tracts: activates postural muscles in limbs and trunk
- medial vestibulospinal tracts: coordinates head and eye movements
Vestibular disease
effects
decreased balance and gaze stability
vestibular disease
signs and symptoms
- vertigo: spinning/cannot focus eyes/feeling of movement
- disequilibrium: feel off balance
- blurred vision with head movement (nystagmus)
dizziness
- a whirling sensation in the head
- giddy
- mentally confused
- off balance
Vertigo
false sense of rotation
oscillopsia
- gaze instability
imbalance
unsteadiness (observable)
disequilibrium
- subjective sense of imbalance
lightheadedness/presyncope
feeling of faintness
Nystagmus
- involuntary eye movement
- abnormal VOR
- slow movements in one direction VOR
- faster movement in opposite direction (saccade)
types of eye movement with nystagmus
- abduction/adduction
- elevation/depression
- torsion
Vestibular nystagmus
based on what is involved
- w/ crystals = nystagmus toward involved side
- w/ vestibular nerve = nystagmus away from involved
goes toward active side
