Vestibular System Flashcards
functions of the vestibular system
move the eyes
neck and body muscle coordination
perception of body orientation
position sense relies on collaboration of..
vestibular system
visual system
proprioception
what does Romberg’s sign test? (standing up straight and closing eyes)
vestibular and proprioception
major structures of the vestibular system and their functions
semicircular ducts - detect angular acceleration
utricle and saccule - detection of linear acceleration
structures of the macula inside the utricle or saccule
otoconium, otolithic membrane, hair cell, supporting cell
what happens when the head tilts to the right?
otoconium will move to the right, causing stereocilia on top of a hair cell to bend to the right.
this changes the membrane potential and alters glutamate release from hair cells, initiating a signal in the bipolar cells of the vestibular ganglion
names of the semicircular ducts
anterior, posterior, lateral/horizontal
what is the significance of the 3 semicircular canals arranged at a right angle to one another?
duplicated signals for each head movement, thus precise head positioning
what fluid is found inside the semicircular canals?
endolymph, ahir cells in the ampullas, activated by endolymph movement
structure that hair cells sit on; what are they embedded in?
crista; semifluid cupula
characteristics of endolymph
similar to intracellular fluid, high in K low in Na
why are they called dendrites of vestibular ganglion cells instead of axons?
they pick up sensory info
hair cells in the utricle/saccule are activated by
otolith movement (this helps detet linear acceleration)
what happens when otoliths get into the semicircular canals?
causes vertigo in the patient
angular acceleration that semicircular canals respond to is actually a response to a change of..
speed
higher speed contributes to this type of firing frequency
higher
if speed is constant, the frequency is
background firing frequency
vestibular connections into the CNS
cerebellum, vestibular nuclei to spinal cord, thalamus to somatosensory cortex, CN 3, 4, 6, reticular formation (pons, medulla)
the vestibular connections into the CNS function to
move the eyes
neck and body muscle coordination
perception of body orientation
the name for the reflex where your head tilts right, eyes move left and vice versa (unconscious)
vestibule-ocular reflex
oculocephalic reflex
doll’s eye reflex
steps of the vestibule-ocular reflex
signals generated in the ampula of horizontal semicircular canals because of endolymph movement, info passes thru vestibular ganglion to nucleus to CN 6, via MLF the info is relayed to CN 4 and CN 3 nuclei
right eye is pulled to the left when CN 3 commands MR to pull
right CN 6 nucleus also talks to lateral rectus to pull, left eye pulled left, right eye pulled left.
brainstem structures important for vestibular-ocular movement connection
vestibular system, MLF, CN 3, 4, 6 nuclei
when the vestibule-ocular reflex is used to test brainstem function in comatose patients its called
oculocephalic reflex
what’s the caloric test?
same vestibular-ocular reflex initiated by irrigating the patient’s warm/cold water; initiates nystagmus due to endolymph movement in the semicircular canals
direction of nystagmus is defined by the..
fast phase (if eyes jerk to the right rapidly, its right-beating nystagmus)
3 ways to induce nystagmus
rotation, cold/warm water into ear, optokinetic
the direction of endolymph flow =
direction of tracking = direction of slow phase nystagmus
cold water into right ear =…
warm water into right ear = ..
left-beating nystagmus
right-beating nystagmus
what does COWS stand for
Cold Opposite, Warm Same.
in a normal person the slow phase is controlled by… the fast phase controlled by…
slow phase= brainstem
fast phase=cerebrum
so in a coma patient with cerebrum not functioning, which phase is apparent?
slow phase only, if brainstem is intact
induction of nystagmus by looking at a continuously moving object
optokinetic nystagmus or railroad nystagmus
what is the optokinetic reflex used to test?
factitious blindness since we cannot suppress this reflex if visual pathway is in tact
what cranial nerves travel through internal auditory meatus?
CN 7 and 8
common tumor at lower pons in the internal auditory meatus
acoustic nerve schwannoma
