Vestibular A&P Flashcards
What are the major functions of the vestibular system?
- Estimate body position and movement
- Postural control
- Control eye movement related to head movement
- Autonomic function and consciousness
What is the peripheral nervous system tasked with as it relates to vestibular function?
- Stabilize images during head movement to allow for clear vision
- Maintain postural stability esp during movement of head
- provide information for spatial orientation
What is inside the bony labyrinth?
perilymphatic fluid and supportive connective tissue
What is the purpose of the bony labyrinth?
protection and communication with CFS via cochlear aqueduct
What lies within the vestibular labyrinth?
bony and membranous labyrinths
What is inside the membranous labyrinth?
Endolymph fluid, vestibule, and semicircular canals
What lies within the vestibule?
otolith organs: utricle and saccule
What is the function of the otolith organs?
relay info about linear acceleration/deceleration of head/neck + static head position
Utricle detects movement in the ________ plane.
horizontal
Saccule detects movement in the _______ plane.
vertical
Otolith organs are _________ to gravity
relative
How do otolith organs detect movement?
movement relative to gravity is detected by the movement of sterocilia/kinocilium; otoconia increase the sensitivity of the movement.
Movement of stereocilia TOWARD kinocilium is _______ (what movement of head?)
excitatory (backward tilt/forward acceleration)
Movement of stereocilia AWAY from kinocilium is ________ (what movement of head?)
inhibitory (forward tilt/backward acceleration)
How do otoliths achieve full spatial representation with regard to movement detection?
positioning of kinocilium and stereocilia provides complete representation for all planes of movement
What is the function of the semi-circular canals?
relay info about angular velocity of head
Are the semicircular canals typically gravity independent or dependent?
Gravity independent
What is the ampulla and what is it’s functional relevance?
bulbous formation at the start/end of each canal
Houses the cupula which holds the stereocilia
Explain the relevance to the directional flow of endolymph fluid in the semicircular canals.
head movement > movement of endolymph in corresponding canal > movement of hair cells in ampulla > depolarization/hyperpolarization
Utriculopedal
movement of endolymph toward the utricle
“pedal towards your destination”
Utriculofugal
movement of endolymph away from the utricle
“Frugal = stay away from spending”
Utriculopedal is excitatory for the ____ canal and inhibitory for the ____ canal
Utriculopedal is excitatory for the HORIZONTAL canal and inhibitory for the ANTERIOR/POSTERIOR canal
Utriculofugal is excitatory for the ____ canal and inhibitory for the ____ canal
Utriculofugal is excitatory for the ANTERIOR/POSTERIOR canal and inhibitory for the HORIZONTAL canal
Explain how the R/L semicircular canals are paired. What movment is each canal most sensitive too?
R + L horizontal canals (30º head tilt + turning L/R)
R anterior + L posterior (45º from midline R, “yes” motion)
L anterior + R posterior (45º from midline L, “yes” motion)
What is the major source of vascularization for the vestibular system?
Labyrinthine artery off the AICA
What are the two branches of the labyrinthine artery and main areas they supply?
- Anterior vestibular a. (vestibular n., utricle, ampullae of anterior and horizontal SCC)
- Common Cochlear a. (cochlea, ampulla of posterior SCC, saccule)
What are the 3 main vestibular reflexes?
- Vestibulo-ocular reflex (VOR)
- Vestibulospinal Reflex (VSR)
- Vestibulocollic Reflex (VCR)
Vestibulo-ocular reflex (VOR)
generates eye movements that enable clear vision while head is in motion
Vestibulospinal Reflex (VSR)
Generates compensatory body movement to maintain head and postural stability.
Vestibulocollic Reflex (VCR)
Acts on neck musculature to stabilize head.
How is normal VOR quantified?
Normal VOR Gain = -1
Vestibulospinal Reflex (VSR)
- head tilts to side
- Ipsi. SCC/otolith excitation
- ↑ input from vestibular nerve > vestibular nuclei ipsilaterally
- MVST/LVST descending drive to truncal muscles.
- ↑ lateral truncal extension ipsilaterally/↑ truncal flexion contralaterally
Three Cervical Reflexes
- Cervico-ocular reflex (COR)
- Cervicospinal Reflex (CSR)
- Cervicocollic Reflex (CCR)
Cervico-ocular reflex
- Interacts closely with VOR
- Eye movements driven by neck proprioceptors
Cervicospinal reflex
Changes in limb position drive by neck afferent activity
Cervicocollic Reflex
Helps stabilize head on body, changes in neck position = afferent input > contralateral reflexive contraction of appropriate neck muscles
What is the general purpose of the cervical reflexes?
They supplement the vestibular reflexes
What is the function of the central vestibular system?
relays information about:
- eye movement control for gaze stability during movement. (oculomotor)
- Postural control and movement (brainstem)
- Spatial orientation (cortex)
- Autonomic nervous system control
What are the four vestibular nuclei?
- Lateral nucleus
- Medial nucleus
- Superior nucleus
- Inferior nucleus
Lateral Nucleus function
Prinicple vestibular relay
Medial nucleus
VOR/VSR relay
Superior Nucleus
VOR relay
Inferior Nucleus
Cerebellar and reticular formation relay
Function of the lateral vestibulospinal tract.
- Head and body position in space.
- Walking upright
- Righting and equilibrium reactions
PONS > thoracic spinal cord to extensor musculature
Function of Medial Vestibulospinal tract
- Head movements
- Integrating head and eye movementa
Medulla > cervical spinal cord extensor musculature
How is the cerebellum involved in vestibular function?
- VOR/VSR suppression (Flocculonodular node)
- Vestibulocerebellar tract: error correcting mechanism, intended v. actual movement
- Cerebellar-Cortical Loop: adaptation of postural responses based on prior experiences (lynx, airport walkways)
What cortical areas are associated with vestibular function? What are each of their
functions?
- Parieto-Insular Vestibular Cortex: PIVC
- Medial Superior Temporal Region
- Ventral Intraparietal Region
Parieto-Insular Vestibular Cortex (PIVC) function
Receives input from cerebellum and vestibular nuclei via the thalamus about visual, somatosensory, and vestibular integration.
Medial Superior Temporal Region Function
- Visuo-vestibular integration
- Self-motion perception
Ventral Intraparietal Region Function
- Spatial orientation
- Proprioceptive, auditory, visual, tactile, vestibular integration
