Lecture 18: Vestibular Anatomy

posture definition

the position of your body in relation to gravity; good posture means training your body to hold these positions with minimal strain on your muscles and ligaments

balance definition

the ability to maintain your posture and prevent falling; related to the forces of inertia acting on your body

when is balance achieved

when your body's bony structure is able to support you with minimal muscle effort (COG within BOS)

postural control definition

the act of maintaining, restoring, or achieving balance while performing an activity or in any posture

postural control strategies can be ________ or _________

reactive or predictive

gaze

the direction of visual attention, usually referring to the position of the eyes in the head or the coordination of eye and head movement

saccade

rapid & jerky voluntary or reflex driven eye movements that jump the fovea from one point of interest to another

nystagmus

involuntary, rhythmic oscillation of the eyes often involving a slow drift followed by a fast correction

saccade vs nystagmus

saccades are normal movements, nystagmus usually indicates a neuro or vestibular disorder

smooth pursuit

steady tracking movements designed to keep a moving stimulus in focus

what maintains horizontal vision during movement

movements of the head and eye

what maintains gaze during movement

movement of both eyes in the same direction, assisted by movements of the head

peripheral vestibular system components

vestibular receptors, vestibular ganglion, vestibulocochlear nerve

what are the vestibular receptors

cupula of semicircular canals, macula of utricle and saccule

what vestibular receptor is for head rotation

cupula in the ampula

what vestibular receptor for linear motion and gravity

macula of utricle and saccule

central vestibular system components

vestibular nuclei, vestibular pathways

there are __ maculae in each ear

2

macula in utricle responds to ________ ___________ and ________ ____ of the head

lateral acceleration and lateral tilt

macula in saccule responds to ________ ____________

vertical acceleration

what are otoliths/otoconia

calcium carbonate crystals on otolith membrane

hair cells synapse with...

vestibular nerve fibers

how many semicircular canals

3; anterior, posterior, horizontal

the crista ampullares are found where

in the ampulla of each canal

what are the crista ampullares

sensory receptors for rotational acceleration

crista hair cells extend into ___ ____ _______ called _______

gel like masses called cupula

anterior canals are activated by

neck flexion, front flip

posterior canals are activated by

neck extension, back flip

horizontal canals are activated by

cranial/cervical rotation, spinning on ice

what canals are activated when turning to the left

left

all 3 semicircular canals are connected to the ______

utricle

loose otolith crystals are called _________

otoconia

otoconia can stick to ______

cupula

CN VII carries sensory info from semicircular canals and maculae to...

cerebellum and vestibular nuclei in pons and medulla

otoliths that break off the macula (otolith organ) in the _______ can enter the semicircular canals

utricle

the 4 vestibular nuclei give rise to both ascending and descending tracts, sending projections to...

cerebellum, brainstem nuclei, cerebral cortex, spinal cord

vestibulocollic and vestibulospinal reflex pathways

medial vestibulotract, lateral vestibulotract

vestibulo-ocular reflex pathway

stabilizes gaze; vestibular nerve --> medial vestibular nucleus --> decussate --> medial longitudinal fasciculus --> CN III/IV/VI

what are the 4 outputs of the vestibular nuclei

VOR, vestibulocollic and vestibulospinal reflex, vestibulocerebellar, vestibulocerebral

muscles responsible for eye elevation

superior rectus, inferior oblique

muscles responsible for depression of the eye

inferior rectus, superior oblique

muscle responsible for abduction of the eye

lateral rectus

muscle responsible for adduction of the eye

medial rectus

muscles responsible for intorsion of the eye

superior oblique, superior rectus

muscles responsible for extorsion of the eye

inferior oblique, inferior rectus

what CNs are responsible for stabilizing gaze during horizontal head movement

III, VI

what CNs are responsible for stabilizing gaze during head nodding

III, IV

vestibulospinal tracts function

maintain balance in the body; responsible for antigravity muscle tone in response to the head being tilted in any direction

vestibulocerebellar pathway

2 way communication intended to improve postural control and balance by influencing activity of the VSTs

vestibulocerebellum

flocculonodular node; vestibular control of eye movement, posture, balance

vestibulocerebral pathway signals end up in the...

frontal eye field, parietal lobe, hippocampus

spinal tract involved in unconscious balance and posture

reticulospinal tract

vestibular nuclei also receive sensory info from

proprioceptors, the eyes

what responds first to proprioceptive signals

spinal reflex pathways (stretch reflex, GTO reflex)

visual info regarding movement of the head relative to the visual environment goes from the ________ _________ to the __________ _______

superior colliculus to the vestibular nuclei