Lecture 5 Flashcards
Vestibular system basics (for what, cortex, vestibular vs proprioception)
NO VESTIBULAR CORTEX
Processes: self-motion, head position, spatial orientation
Important for : balance, gaze stabilization, head movement
Degrees freedom: 3 w/ rotation
vs. proprioception:
vestibular → MOVEMENT
proprioception → POSITION
the labyrinth (basics. parts, 3) Where are the endolymph & perilymph?
Continuous w/ cochlea
Uses stereocilia for linear acceleration & velocity
Utricle & saccule (otolith organs)
Three ampullae (semicircular canals)
Endolymph: apical, bathes hair cell bundle
Perilymph: surrounds basal portion
Otolith organs (hair cells & types of movement)
- Linear acceleraton & head tilts
- Dual hair cells populations
-> orientation switches at striola - Sacclule hair bundles are vertical
- Utricle hair bundles are horizontal
(see 5.3)
Macula (&s RPs)
ensory epithilium
- otolithic membrane (otocania embedded)
- reticular membrane
Hair bundles project into OM
Head tilts & acceleration → OM shifts → hair bundles moves →RP!
(head upright → vestibular afferents steadily fire)
(see 5.4)
Semicircular canals
- Angular acceleration & head rotation
- Hair cells in SAME direction
- 3 axes of motion → 3 canals
Crista (& RPs)
Sensory epithilium (see 5.6)
- ampulla
-cupula
-crista
On canal plane:
hyper & depolarization
Orthogonal: little to no change
Hair bundles projects into cupula
Rotational movement → cupula distorts away from movement → hairbundles moves → RPs!
Angular acceleration & speed
Constant velocity → return to base line
Inc & Dec during acceleration & deacceleration
(see 5.7 for Speed and Firing)
Bonus: push - pull w/ opposite side of head canal
Vestibular processing: reflex (2 classes) & senses
Reflex:
maintaining eg. gaze during movement
maintaining posture/balance
Senses: multisensory, also gets visual info
Vestibular processing: integration
Integrates from:
- canals
- otoliths
- contralateral vestibular nuclei
- cerebellum
- visual & somatic sensory systems
Vestibular ocular reflex (VOR)
To fix gaze during movement (counters)
PATH: (see 5.10)
ex: head turns left → medial & lateral VN → (MVN) abducens nucleus → oculomotor nucleus → medial & lateral rectus
[END eye movement to R ( ↓ RMR & LIR, ↑LMR & RIR)]
Physiological nystagmus
Caused by net difference in L&R vestibular nerves firing rates
Slow eye movement counter to rotation
Fast movement in same direction to “reset”
Spontaneous nystagmus
Caused by net difference in L&R vestibular nerves firing rates
Damage to one nerve
Eye movement in ABSENCE of head rotation
VOR clinical evaluation
Unconscious: caloric tracking
Conscious: use of cold & water water
> Cold → slow movement toward ear fast away from ear
> warm → opposite
loss of VOR & oscillopa
Oscillopa: “bouncing vision”
Unilateral damage compensated
Bilateral damage not
Vestibulocervical reflex
For: head postion & neck muscles
Path: semicircular canals → medial VN axons descent through MLF to upper spinal cord
ex: downward path → neck muscles reflectively pull head
“descending projection”
