Abnormal balance: vestibular and cerebellar disease Flashcards
(35 cards)
What is the role of the vestibular system
sensory system
maintains balance
maintains appropriate position and movement of eyes, neck, trunk, limbs
detects head motion
regulated LMN innervating muscles in neck and body
What CN receives vestibular hair cell receptor info?
CN VIII
What do the utricle and saccule detect?
head position and linear acceleration
What do the 3 semicircular ducts detect?
angular acceleration aka head rotation
when CNVIII is not equally activated on L and R
What are the 5 efferent outputs of the vestibular system?
UMN spinal cord tracts
connections to brainstem nuclei of CNs III, IV and VI
cerebellum
cerebral cortex
vomiting center
What is the effect of activating the vestibulospinal tracts?
increase ipsilateral extensor tone
decrease contralateral extensor ton
aka accomodated for weights shifts
What is the effect of the vestibular system on the CN III, VI and IV?
enable coordinated conjugate eye movements in responses to changes in head position
What is the physiological nystagmus?
eyes moving in a jerky fashion
eyes remain focused on original target but jerk in direction of the head movement to maintain a steady gaze while moving
= vestibulo-ocular reflex
What is the afferent and efferent inputs for the vestibulo-ocular reflex?
afferent: CN VIII
info through brainstem
effrent: CN III, IV, VI
What is the role of the the vestibulocerebellum?
flocculonodular lobe
recieved afferent input from vestibular nuclei
cerebellar efferent output is inhibitory to vestibular nuclei: releases GABA
What is the role of the forebrain in the vestibular system?
axons travel from vestibular nuclei to contralateral vestibular cortex
enable conscious perception of balance and position
How does disease affect the vestibular system?
at rest we have equal tonic input of L/R vestibular nuclei
head movement = unequal activation
when disease compromises one side = percieved as movement
reflex changes in posture and eye movement causing the clinical signs
What are clinical signs of vestibular system dysfunction?
head tilt
abnormal balance: vestibular ataxia
tight circling
pathological nystagmus (when no head mvt)
abnormal vestibulo-ocular reflex
positional strabismus
nausea
What does the head tilt tell us aout the vestibular system dysfunction?
towards the side of the lesion!
due to decreased extensor tone (least vestibular activity) on side of lesion/ increased tone on contralateral side
What is the difference between a physiological and pathological nystagmus?
physiological: when head moved
pathological: at rest due to disrupted vestibular input
(fast phase away from lesion)
What is a positional strabismus?
abnormal eye position
raising the head results in ventrolateral deviation of eye on affected side
What are types of peripheral lesion of vestibular system?
compromise CN VII
sympathetic innervation to eye
close to tympanic bulla
What are types of central lesions affecting vestibular system?
other CN nuclei
ascending proprioceptive tracts from spinal cord (proprioceptive ataxia)
descending UMN tracts (tetraparesis)
ascending reticular activating system (abnormal mentation)
LOOK FOR brainstem dysfunction signs
What are clinical signs only seen in central vestibular disease?
vertical nystagmus
nystagmus chages direction with changes in head position
possible proprioceptive deficits and/or paresis
What is the difference in consciousness in central vs peripheral vestibular disease?
central: obtunded, stuporous, comatose
peripheral: normal, disorientated
What is the treatment and prognosis for idiopathic vestibular disease?
peracute onset, no central involvment, typically older dogs
tx: supportive - antiemetics, IVFT, nursing care and hand feeding
prognosis: good, possible residual head tilt
What is the function of the cerebellum?
regulate rate, range and forve of movemnt
coordinates movement
ensures appropriate posture
maintains equilibrium
afferent and efferent info stays ipsilateral
What is the afferent and efferent path of cerebellum function?
receives proprioceptive info from muscl spinfles, golgi tendon organs, vestibular system (informed by head and body)
receives info from motor cortex in forebrain on intended movements
modulates motor activity: ensures appropriate posture and desired movement of appropriate rate range and force
What are some signs of cerebellar dysfunction?
cerebellar ataxia
truncal ataxia/sway
wide based stance
hypertonus (spasticity)
decerebellate posture
intention tremor
abnormal menace response
- unilateral lesion = ipsilateral clinical signs
if lesion of vestibylocerebellum: vestibular ataxia, head tilt, positional and pathological strabismus
