Lecture 24: Vestibular System Flashcards
Two components of the vestibular system
- Semicircular canals- angular acceleration
- Otoliths- linear acceleration
Where is the vestibular organ located?
Temporal bone
What supplies blood to the vestibular organ?
AICA, Internal auditory artery
Describe vestibular hair cells
- Hair cells have stereocilium that gradually get longer across the cell
- Kinocilium causes hair cells to activate
- Otoliths on top of a fibrous membrane help activate the cells by being displaced during acceleration
- Maculae of the utricle and saccule are in different planes, so they can measure movement in three dimensions
Describe the ampulla in the vestibular organ
- At the end of each semicircular canal
- Contain sensory epithelium, cristae, where the hair cells are
- Hair cells embedded in gelatinous mass (cupula)
- Fluid flows past and causes kinocilia when the head is moved
- Info from each ear is integrated to determine movement
Where is the vestibular nuclei located in the brainstem?
At the pons/medulla junction
Where does the vestibular nuclei project to?
- Cerebellum for motor correction
- Contralateral vestibular nerve
- Extraocular muscles for gaze stabilization
- Spinal cord via vestibulospinal path for posture adjustment
Area of brain that processes vestibular information
Parietal operculum
Bilateral but stronger on ipsilateral side
How does the vestibular system interact with the cerebellum?
Vestibular system gives info about where the head is moving so the cerebellum can make corrections
What is the vestibulo-ocular reflex?
Keeps the eyes still in place while the head moves
What is the vestibulo-cervical reflex?
Keeps the head level when walking
What is the vestibular-spinal reflex?
Adjusts posture for rapid changes in position; via vestibulospinal path
What does the otolith signal mostly act on?
Spinal cord via lateral vestibulospinal tract in ventral funiculus; ipsilateral
Acts on proximal muscles in legs/arms to adjust for head movements
How do semicircular canal inputs reach the spinal cord?
Medial vestibulospinal tract
Mostly but not all ipsi; mostly to cervical segments
What semicircular canals sense rotation in which plane?
- Horizontal canals- horizontal plane
- Vertical 45° to the left: LARP
- Vertical 45° to the right: RALP
Describe how the vestibular system moves the eyes
Optokinetic nystagmus
Eyes will snap to the other direction when the head rotates away from something too far
Artificial activation of optokinetic nystagmus
- Inject water into ear
- Cold opposite; warm same (COWS)
- Warm water in left ear causes eyes to turn right and snap back to left
- Cold water in left causes eyes to turn left and snap back to right
Benign Paroxysmal Vertigo
Otoliths can fall off membrane and get stuck in cupola and cause hair cells to sense gravity = vertigo in certain position
Can rotate head a certain way to get them back
