The vestibular system Flashcards
what are the 5 components of the vestibular system?
1- peripheral receptor apparatus
- in the inner ear
- vestibular and cochlear share the same place
2- central vestibular nuclei
4 nuclei
3- vestibulo-ocular network
-horizontal gaze
4- vestibulospinal network
-posture and balance
5- vestibulo-thalmo-cortical network
-provide neck proprioception
what are the 2 types of movement?
angular –> semicircular canals –> CNS
linear –> saccule & utricle –> CNS
CNS–>
forebrain: perceived orientation
SC & cerebellum: postural control
oculomotor system: eye movements
where is the peripheral vestibular labyrinth (inner ear) located?
lateral and posterior to the cochlea
what is the peripheral vestibular labyrinth made up of?
1- bony labyrinth- several cavities in the petrous portion of the temporal bone
2-membranous labyrinth- resides in the bony labyrinth- fine membranes made up of a simple epithelium
- specialized region= a sensory epithelium
- filled with endolymph
- surrounded with perilymph
what is perilymph?
fluid that fills the space between the bony labyrinth and the membranous labyrinth – protects
what is endolymph?
fluid fills the membranous labyrinth
what are the 2 main parts of the membranous labyrinth?
1- the static labyrinth
2-the dynamic labyrinth
what is the static labyrinth?
a pair of otolith organs
- utricle (horizontal epithelium)
- saccule (verticle epithelium)
maintain balance and equilibrium, eyes in horizontal gaze
only works in gravitational environment
linear acceleration
what is the dynamic labyrinth?
pair of 3 semicircular canals
- anterior/superior
- lateral/horizontal (angled up 30 degrees)
- posterior
rotatory accelerations and decelerations
important in eye fixation with head movement (smooth pursuit)
doesn’t need gravity
works by inertia
works in outer space
what are the functions of the static labyrinth?
monitors the absolute position of the head in space
-assists in posture and balance
maintenance of eye position
perception- linear accelerations and decelerations
**needs gravity to work.
pitch and roll are static
what movement is pitch?
flexion/extension
what movement is roll?
lateral bend
what movement is yaw?
rotation
within the membranous labyrinth are 2 swellings:
utricle
saccule
what is a macula?
a specialized receptor within both the urtricle and saccule
horizontal orientation in the utricle
vertical orientation in the saccule
contains hair cells that synapse on the distal branches of the vestibular ganglion cells
what is a stereocilia?
the apical surface of each hair cell
what is a kinocilium?
on one side of the stereocilia
what is otoconia?
consists of calcium carbonate crystals
lies in a gelatinous substance that overlie the hairs
what is striola?
a structural landmark consisting of small otoconia arranged in a narrow trench that divides each otolith organ
in the utricular macula, the kinocilia are directed toward the stroll
in the saccular macula, the kinocilia point away from the stroll
*note that given that the utricle and sacculus are on both sides of the body, there is a continuous representation of all directions of body movement
what is an otolith?
group of otoconia together
when hair cells bend stereocilia toward kinocilium..
the cell becomes depolarized
what the stereocilia bend away from the kinocilia:
the cell becomes hyper polarized
what are tonic labyrinth reflexes?
???
supine: extension of UE and LE
prone: flexion of UE and LE
sidelying:
extension of limbs touching floor
flexion of limbs facing up
trendelenburg positon:
UE: extension
LE: extension
what are functions of the semicircular canals?
dynamic
- enables us to track the rotation of the head in space
- perception of angular acceleration and deceleration
important with eye fixation movement- eyes move first in a saccade and then the head turns
help with balance, equilibrium, maintaining tone in body
if the anterior canal is stimulated on the R side then the :
posterior canal on the L side is inhibited
*horizontals work together
each semicircular canal contains:
one enlarged end = ampulla
what resides in the ampulla?
ampullary crest (crista ampullaris) a ridge that bears hair cells like those of the maculae
what covers the ampullary crest?
cupula- a gelatinous capsule - extends upward to the roof of the ampulla
when endolymph moves toward ampula it:
pushes against the cupola and bends the hair cells away which facilitates the system (depolarization)
when endolymph moves away from the ampula it:
decreases AP (inhibits) because hair cells and cupola go the other direction
what is the oculocephalic reflex?
doll’s eye maneuver
briskly turn head to one side or the other or tilt up and down
eyes turn in the opposite direction= intact BS pathway
what are the clinical uses?
increase tone- phasic, quick movements
decrease tone- slow, rhythmic movements
autonomic responses
decreases in: BP, respiration, HR, body temp (by dilation of BVs)
Increases: peristalsis
diseases of the vestibular system can take different forms and usually induce:
4 cardinal signs
vertigo
instability
nystagmus
often accompanied by nausea
what are the most common diseases of vestibular system?
vestibular neuritis
benign paroxysmal positional vertigo (BPPV)
what is benign paroxysmal positional vertigo (BPPV)?
pieces break off the otoliths slipped into one of the SSC
most cases it is the posterior canal
in certain head positions, these particles shift and create a fluid wave which displaces the cupola of the canal affected, which leads to dizziness, vertigo and nystagmus
