vestibular system Flashcards
what are responsible for angular motions?
semicircular canals
what is responsible for linear motion?
vestibule
what is perilymph?
CSF and is high and Na
this is outside of membrane
sits between the bone and the membrane
what is endolymph?
fluid that is high in K
this is inside of membranes
what are the three semicircular canals?
superior
posterior
horizontal
what motion would the superior semicircular canal detect?
a nod for yes (up and down)
what motion would the posterior semicircular canal detect?
head tilt left or right (ear towards shoulder)
what motion would the horizontal semicircular canal detect?
shaking head no ( left and right axial rotation)
how do the semicircular canals overcome inertia?
the cupula is a sack that covers the hair cells. The sack is full of endolymph
what are the organs that make up the vestibular system?
utricle and saccule
(otolithic organs)
these sense linear motion
gravity
what are otoconia?
calcium crystals, these move with gravity. as you go up the move up and as you go down they hit the hair cells.
what is the striola?
the bag that holds the otoconia
what is the otolith membrane?
the sack to covers the hair cells and is what moves the hair cells depending on the movement
what does multimodal convergence mean?
immediate integration with other sensory inputs
where is the central vestibular nucleus located?
pons/medulla
dorsal portions
what are the four major central vestibular nuclei?
superior(all in the pons) lateral, medial, and inferior vestibular nuclei
with cilium how are the potassium channels open?
stretch activated
depending on the direction of bend, it will either activate or slow down the signal
in the utricle and saccule how are the hair cells aligned?
in opposite directions
where are the hair cells located in the semicircular canals?
in the ampulla of each canal
what does the horizontal canal do?
adjusts your eyes based on head movement via the superior vestibular nucleus
Vestibulo-cerebellar network
superior vestibular nucleus
-impulse directly from the semi circular canals that goes to the cerebellum.
-coordination of:
posture
balance
eye movements (saccade control) fast movements of the eyes.
Vestibulo-ocular network
- horizontal canal to the superior vestibular nucleus.
- horizontal eye movement.
- *control is in the pons**
what is nystagmus?
eyes drift/jerk to the opposite side of head movement first(slow) and then quickly jerk to the side of motion.
pathway from the horizontal canal to the muscles?
vestibular nucleus (superior, pons) to the abducens nucleus (pons) and then to the contralateral lateral rectus and oculomotor (along the medial longitudinal fasiculus)
how do you test the vestibular function?
caloric vestibular stimulation (CVS)
galvanic vestibular stimulation (GVS)
sound-induced vestibular stimulation
Vestibulo-ocular
caloric nystagmus test
- subject tilts head back to make horizontal canal vertical
- ear is irrigated with either warm or cold water
- nystagmus is the result
example of caloric nystagmus with warm water in the right ear
**tests for intact pons
endolymph expands(rises) causing motion towards the utricle
-slow phase: eyes left initially
-fast phase: corrective saccade to the right
cold water will do the opposite.
whatever side the warm water is put in is the side of the fast saccade
what does COWS mean in terms of caloric nystagmus?
C cold opposite O opposite W warm S same **reference to fast response**
caloric nystagmus signs
slow phase absent
horizontal canal weakness (ipsilateral)
damage to the MLF/pons
caloric nystagmus signs
fast phase absent
cerebral damage
caloric nystagmus signs
both phases lost
bilateral hindbrain
very poor prognosis
vestibulo-thalamo-cortical
vestibular nuclei(superior, lateral, and inferior) of the pons and medulla to the thalamus to the cortex
- top down control
- mostly angular motion with some utricle saccule (linear)
- *only thalamic relay
vestibulo-spinal
lateral and medial vestibulospinal tracts
response to linear motion (utricle and saccule)
in the medulla
the lateral vestiubulospinal tract interacts with what?
excitatory or inhibitory
the alpha motor neurons
excitatory output of upper limbs, head, neck, back, and legs
the medial vestibulospinal tracts interacts with what?
excitatory or inhibitory
alpha motor neurons but is inhibitory for the most part.
inhibitory output to neck and back
what is subjective vertigo?
the person feels as if they are spinning
-vestibular system injury
what is objective vertigo?
the room is spinning
-central vestibular issues
what do the medial and lateral vestibulospinal tract travel in?
the medial longitudinal fasiculus (MLF)
vestibular signs and symptoms
balance: steadiness, symmetry, dynamic stability, gait deficiencies
dizziness: lightheadedness, unsteadiness, giddiness, faintness, mental confusion, **imprecise
what is an acoustic neuroma (shwannoma)?
benign tumor that produces pressure on CN VIII
symptoms: unilateral nystagmus, vertigo, tinnitus, hearing loss.
