Vestibular Anatomy Flashcards
what are the roles of the vestibular system?
- estimate body position and movement
- postural control
- control of eye movements
- autonomic function and consciousness
- project info throughout cortex, brainstem and cerebellum
define pitch
rotation around y-axis
nodding yes
define yaw
rotation around the z-axis
shaking head no
define roll
rotation around the x-axis
tilting head side to side
what structures are included in the central vestibular system?
- vestibular nuclei (4)
- vestibular tracts (6)
- vestibulocerebellum
- vetibular cortex
what structures are included in the peripheral vestibular system?
- vestibular apparatus
- bony labyrinth
- otolith organs
- semi-circular canals
- CN 8 - vestibular branch
what are the primary functions of the peripheral vestibular system?
- stabilize visual images on fovea of the retina during head movement allowing for clear vision
- maintain postural stability (especially during movement of head)
- provide info for spatial orientation
the peripheral vestibular system is mainly responsible for ______________
relaying info (velocity and acceleration of the head)
what is included in the vestibular apparatus?
- bony labyrinth
- membranous labyrinth
what structures make up the membranous labyrinth?
- Vestibule
- Otolith organs (utricle and saccule)
- Semicircular canals
- anterior canal
- posterior canal
- horizontal canal
- Cochlea
what is the role of the otolith organs?
linear acceleration/deceleration
static head position
what is the role of the utricle and saccule?
- Utricle → detects movement in the horizontal plane
- Saccule → detects movement in the verticle plane
what are stereocilia?
- gravity-dependent motion sensitivity
- hair cells encased in gelatinous layer (macula)
- layered on top: Otoconia
- calcium carbonate crystals
- heavier than structures it overlays
describe how stereocilia work
- Motion receptors → transduce minute displacements into behaviorally relevant potentials
- movement of stereocilia towards kinocilium = excitatory
- movement of stereocilia away from kinocilium = inhibitory
how do the semicircular canals function?
they are encased in the bony labyrinth and filled with endolymph
- head rotation → movement of endolymph in corresponding canal → movement of hair cells → depolarization/hyperpolorization
what are ampulla?
bulbous formation at the start or finish of each canal
contains cupula, which houses stereocillia
which are sensitive to angular movements only
hair cell displacement towards the utricle is called _______
utriculopedal cupular displacement
hair cell displacement away from the utricle is called _________
utriculofugal cupular displacement
utriculopedal cupular displacement is excitatory/inhibitory for what?
- Excitatory → horizontal canall
- Inhibitory → anterior/posterior canal
utriculofugal cupular displacement is excitatory/inhibitory for what?
- excitatory → anterior/posterior canal
- inhibitory → horizontal canal
list and briefly describe the vestibular reflexes
- Vestibulo-Ocular Reflex (VOR)
- stable vision during head motion
- Vestibulo-Spinal Reflex (VSR)
- stable body during head motion
- Vestibulo-Collic Reflex (VCR)
- stable neck during head motion
Describe VOR connections to ocular nuclei
labyrinth → vestibular nuclei → ascending tracts (cross at MLF) → ocular motor nuclei (III, IV, VI)
excite/inhibit the agonist/antagonist muscles needed to move the eyes in the desired direction
describe what occurs within the horizontal canals when turning the head to the left
- left horizontal semicircular canal → the endolymph is pushed towards the utricle → utriculocupular displacement = excites horizontal canal
- right horizontal semicircular canal → the endolymph is displaced away from utricle → utriculofugal displacement = inhibits horizontal canal
what is the purpose of the VSR?
generation of compensatory body movements to maintain head and postural stability
list the steps involved in the VSR
- head tilts to side
- ipsilateral SCC/otoliths excitation
- increased input from vestibular nerve → vestibular nuclei ipsilaterally
- MVST/LVST descending drive to truncal muscles
- increased truncal extension ipsilaterally and increased truncal flexion contralaterally
what is the purpose of the VCR?
similar to VSR only works on the cervical musculature
it counters a movement sensed by our labyrinth otolithic or SCC and modulates neck movements accordingly to help with postural stability
list the cervical reflexes
- Cervico-ocular reflex (COR)
- Cervicospinal reflex (CSR)
- Cervicocollic reflex (CCR)
describe the COR
- interacts closely with VOR
- can supplement VOR under certain circumstances
- eye movements driven by neck proprioceptors
describe the CSR
- changes in limb position driven by neck afferent activity
- can supplement VSR under certain circumstances
describe the CCR
- helps stabilize head on body
- afferent input caused by changes in neck position (stretch) → contralateral reflexive contraction of appropriate neck muscles
what structures are involved in the central vestibular system?
- Vestibular nuclei
- Lateral/Medial nucleus
- Superior/Inferior nucleus
- Vestibular tracts
- Medial/Lateral vestibulospinal
- vestibulocerebellar
- Vestibulocerebellum
- Vestibular Cortex
what are the functions/relay points of the vestibular nuclei?
- eye movement control for gaze stability during movment (oculomotor)
- postural control and movement (brainstem)
- aid in maintaining tone
- spatial orientation (cortex)
- autonomic nervous system control
describe the lateral vestibulospinal tract
travels to the thoracic spinal cord to extensor muscles
- head and body position in space
- walking upright
- righting and equilibrium reactions
describe the medial vestibulospinal tract
travels bilaterally to the MLF to the cervical cord to extensor muscles
- head movements
- integrating head and eye movements
what is the role of the vestibulocerebellum?
responsible for postural and gaze stabilization
- modulating VOR
- VOR suppression/cancellation
- VSR suppression/cancellation
how is the thalamus involved in vestibular function?
- VPL of thalamus connects subcortical structures to the vestibular cortex
- connection w/vestibular cortex and reticular formation for arousal and conscious awareness of body
- specific vestibular info processed in VPL
what specific vestibular info is processed in the VPL?
- discrimination between self movement vs. that of environment
- spatial awareness and perceived vertical
- “personal space”
List cortical regions involved in the Vestibular Cortex
- PIVC (parieto-insular vestibular cortex)
- junction between parietal and insular lobe
- thalamus connects it to cerebellum and vestibular nuclei
- Medial superior temporal region
- visuo-vestibular integration
- self-motion perception
- Ventral Intraparietal region
- multisensory spatial coding
- proprioception, auditory, visual, tactile, vestibular
How is the vestibular system involved in autonomic function?
it has many projections throughout the brainstem to the reticular formation and other regions involved in autonomic function
