9-2 Flashcards
How many semicircular canals
3
Names of each semicircular canal
- Superior/anterior
- Lateral/horizontal
- Posterior
Superior/anterior plane
Sagittal
Superior/anterior movement
Nodding your head
Lateral/horizontal plane
Transverse plane
Lateral/horizontal movement
Checking both sides of traffic
Posterior plane
Coronal
Posterior movement
Head touch either shoulder, cartwheel
What do the semicircuclar canals detect
Head rotation
Where does head rotation arise from
Self-induced head rotation or angular accelerations imparted by external forces (such as merry go round)
What is the ampulla filled with
endolymph
Gelatinous mass that bridges the canal of the ampulla
Cupula
The cuplua blocks ____
flow of endolymph
In the cupula, all stereocilia are orientated in the same/different direction
Same
Is there striola in the ampulla
No
What contains hair cells in the ampulla
Crista (epithelium)
The cupula extends from ___ to ___
crista
top of ampulla
Hair cells in the ____, stereocilia in the _____
Crista
Cupula
Endolymph moves in the same/opposite direction of acceleration
Opposite
What happens when the endolymph flows in the opoosite direction of head rotation
Stereocilia move towards kinocilia (depolarize)
Movements in relation to head movement for:
- SCC depolarization
- Eye movement
- Endolymph movement
- Same direction
- Opposite direction
- Opposite direction
AP at constant velocity
Slightly higher than basal level discharge
Major classes of vestibular relfexes
- Vestibulo-ocular reflex (VOR)
- vestibulocervical reflex (VCR)
- vestibulospinal reflex (VSR)
VOR
Produces eye movement that counters head movement
VCR
Produces postural adjustment of the head
VSR
Produces postural adjustment of the body
Bilateral loss of VOR leads to ____
oscillopsia (bouncing vision - eyes move along with the head)
Most of the time, oscillopsia is due to
Unavailability of vestibular information to the occulomotor nucelus (ex: stroke in this region)
Intact ___ is essential for VOR
brainstem
Where does most damage in the brainstem happen
Medial longitudinal pascilculus
Why does the eye move with the head in oscillopsia
All connections are lost
What is not working in oscillopsia
Brainstem
What is not working in supernuclear gaze palsy
Cebrebral cortex
Presentation of supernuclear gaze palsy
Will still have VOR but cannot voluntarily rotate eyeballs
Alexander’s law
Refers to spontaneous nystagmus that occurs after an acute unilateral vestibular loss
Test of vestibular function
Caloric testing
Vestibular problems can arise in:
- Semicircular canal
2. Nerve tracts
Warm water irrigation effect
- Endolymph moves (mimics head turning)
- Increases firing rate
Cold water irrigation effect
- Decreases endolymph movement
- Decreases firing rate
Fast eye movement
Saccades
Slow eye movement
Physiological nystagmus
What happens when the eye moves all the way to one side
We need to make a fast correction to bring it back to the other side
Baseline firing on one side and no firing on the other side
There is a difference, so the eye will spontaneously move and correct back again (leads to vertigo)
Vertigo
Feeling of moving when you are not (dizziness, motion sickness)
Damage to the vestibular system:
- Menieres disease
2. Vestibular nerve section
Menieres disease
The ear feels full because there is too much endolymph in the sac. Starts unilateral and progresses to the other ear
Vestibular nerve section
Does not progress. CNS compensates
Eye is always moving towards warm/cold water
Cold
Decebrebrate rigidity
Characterized by rigid extension of the limbs
When does decrebrate rigidity arise
When the brainstem is transected/cut above the vertebral nuclei
___ is importain for maintaining muscle tone
Vestibular system
___ suppresses ____ to prevent excessive muscle tone rigidity
Cerebral cortex
Vestibular nuceli
What happens when the cerebral cortex is removed
Rigidity
What types of stimuli does the vestibular cortex respind to
Vestibular, proprioceptive, and visual
Lesion to the vestibular cortex leads to
Altered perception of personal and extrapersonal space (contralateral neglect syndrome)
