Vestibular Anatomy Flashcards
Signs and Symptoms of Vestibular Dysfunction
Dizziness Blurry Vision Nystagmus Tinnitus Vertigo Hearing loss Loss of balance & possible falls Broad-based stance (to accommodate for imbalance) Sweating, nausea, and vomiting (due to ANS involvement)
What are the two main reflexes of the vestibular system?
VOR: Vestibulo-ocular Reflex
VSR: Vestibulo-spinal Reflex
What are head movements detected by?
cupula
Vestibulo Ocular Reflex
Stabilizes eye in space
Necessary to see while head is in motion
Components of VOR:
angular and linear VOR
Vestibulo-Spinal Reflex
Stabilizes body
Helps maintain desired orientation to environment
Cervical Reflexes
cervicoocular reflex
cervicocollic reflex
cervicospinal reflex
Cervicoocular Reflex (COR)
Weak reflex
Does not play direct role in gaze stability
May help VOR to compensate
Proprioceptors and somatosensory receptors
-C1-C2 dorsal nerve roots
Cervicocollic Reflex (CCR)
Provides head stability
Contraction of stretched muscles to align head
Cervicospinal Reflex (CSR)
acts in conjuction with the VSR
-provides postural stability through limb activation
Three axes of rotation:
roll
pitch
yaw
Three axes of translation
AP
lateral
vertical
Pitch:
up and down
Yaw
head movement side to side in horizontal plane (shaking head no)
Roll
lateral side bending
What do semicircular canals detect?
angular rate
What do otoliths (saccule and utricle) detect?
linear acceleration
Functions of peripheral vestibular system:
Stabilization of visual images on the fovea of the retina during head movement to allow clear vision
Maintain postural stability especially during movement of the head
Provide information used for spatial orientation
Peripheral vestibular components:
Semicircular canals (SCC)
Utricle
Saccule
CN VIII: Vestibulocochlear nerve
Orientation of semicircular canals:
Anterior/superior
Lateral/horizontal
Posterior/inferior
What are the components of the labyrinth?
bony
membranous
Bony labyrinth:
3 semicircular canals
cochlea
vesitbule
What is the bony labyrinth filled with?
perilymphatic fluid (similar to cerebral spinal fluid)
What is the membranous labyrinth?
suspended within the bony section and contains membranous portions of the canals and utricle and saccule
What is the membranous labyrinth filled with?
endolymphatic fluid (similar to intracellular fluid)
Ampulla:
contain the cupula (hair cells) which convert displacement into neuro firing thru bending of hair cells
What does ampulla detect?
linear/angular motion
Otolith Organ
(Utricle and Saccule): contain calcium carbonate crystals called otoconia
What does otolith organ detect?
gravity and acceleration
Sensory organ of angular VOR:
Semi-Circular Canals:
Horizontal
Anterior
Posterior
Which direction do eyes move with angular movement?
opposite
Pitch is sensed by what?
anterior/posterior canals
Yaw is sensed by what?
horizontal canals
Sensory organ of linear or translation VOR
Otoliths:Saccule and Utricle
Which direction do eyes move with linear movement?
opposite
What does the saccule detect?
Linear movement up and down (riding in elevator)
What does the utricle detect?
Linear movement horizontally (riding on a train on a straight track
Sensory organ of ocular tilt reflex:
Otolith:Utricle
What direction do eyes and head move in ocular tilt reflex?
opposite tilt of head
What does head tilt to the left cause?
elevation of the left eye, depression of the right eye, torsion of both eyes to the right and the tilt of the head on the body to the right.
What facial nerves does ocular motor nuclei travel for mediation of VOR?
III,IV,VI
What are the target for vestibular input?
Vestibular Nuclear Complex
The cerebellum
What does the cerebellum do?
back-up system for adaption of gain of VOR
Monitors vestibular performance and readjusts central vestibular processing if necessary
VOR (Vestibular Ocular Reflex):
generates eye movements, which enables clear vision while head is in motion
VSR (Vestibular Spinal Reflex):
generates compensatory body movement in order to maintain head and postural stability, thereby preventing falls
VCR (Vestibular Collic Reflex):
stabilizes the head in space
Function of vestibular system:
stabilizes vision when head moves (VOR) balance control (VSR)
What does visual acuity depend on:
position of image on fovea
ability to hold image steady
Position of image: gaze shifting
for best vision, object within 0.5 of center of fovea
fovea must be moved to achieved proper poistion for vision
saccades, pursuits, vergence eye movement
Holding image steady, gaze holding
optokinetic, visual fixation, vergence and vestibular eye movements
Components of balance control:
gaze stabilization system
postural stabilization system
Gaze Stabilization System
maintains gaze direction of the eyes and visual acuity during activities involving active head and body movements
Postural Stabilization System
keeps the body in balance while an individual stands and actively moves in daily life
