Vestibular, balance and locomotion

base of support

area bounded by the points of contact between the feet and ground - large base = more support

romberg test

challenges balance and used to measure postural stability - performance judged by trained clinician

centre of gravity

average position of all the mass of an object - also center of mass

controlling standing balance involves keeping

CoG within the base of support - the body is inherently unstable and gravity pulls down results in torques upon the different joints

force of the floor pressing back against the cane is called

ground reaction force

centre of pressure is calculated from the

ground reaction forces, and represents the summed/total ground reaction force

when standing still we are constantly

swaying about the anterolateral and mediolateral planes - small and slow movements

the pressure we apply under the feet (CoP) is said to

herd/corral the more slow movement of the body CoG

simplified model that captures the major aspects of standing balance

inverted pendulum - like shooting a firearm

gait cycle

rhythmic pattern of movments made when walking/running and 2 phases

stance/swing

bi pedal walking

mode of locomotion where the legs move in antiphase - one foot is in contact with the ground at all times - both feet at ground briefly

bi pedal running

locomotion where both legs move in antiphase - but both feet are never at the ground at the same time.- periods where nothing is contact with the ground - flight periods

quadrapedal locomotion

different and distinct patterns from bi pedal locomotion

as we move further away from the ankle

more sway - ankle is the main point of rotation

so shoulders would have a lot more movement than ankles

larger movements in centre of pressure than

centre of gravity

Gastrocnemius and soleus push us __, anterior tibialis

back - forward sway, push forward - backward sway

sot 5 is sensitive to

vestibular dysfunction

semicircular canals anatomy

6 in head, anterior, posterior and horizontal planes

head rotation

otolith anatomy

utricle and saccule

linear motion

vestibular hair receptors at rest

some stretch gates k+ channels are open - giving the afferent a background/spontaneous firing rate

deflection of stereocilia in their preferred direction (kiinocilium away from midline)

decreases inward k+ current - hyperpolarizes the hair cell receptor so it releases less glutamate

labyrinth is filled with

endolymph - potassium concentration is higher than sodium concentration

at rest k+ channels are

open - afferent has a base line firing rate

when the kinocilium is deflected away from midline

more k+ channels open - increase afferent firing

when the kinocilium is deflected towards midline

k+ channels close - decrease afferent firing rate

each SC canal has

1 ampula - compartment containing hair cell receptors and a gelatinous cupula - where hair cell receptors are embedded

head stationary

sc canal and endolymph fluid inside the canal is not moving - hair cell afferents are firing at baseline - spontaneous levels

head rotation

sc canal is rotated to the left - endolymph stationary at first then presses up against the cupula, deflecting it and the hair cell receptors inside

acceleration about the vertical axis

stimulates horizontal canals, not anterior or posterior canals

acceleration about the back to front axis

stimulates the anterior and posterior canals

acceleration about the ear to ear axis

stimulates the anterior and posterior canals

saying no activates

horizontal SC canal

when the head keeps rotating at a constant speed

endolymph moves with skill and doesnt deflect cupula

but when it stops it bends them in the anti preferred direction

otoconia

tiny chalk crystals embedded in the gelatinous otolithic membrane

calcium bicarbonate

when the head is held tilted or accelerated in a linear fashion the

mass of the otoconia under gravity pulls the otolithic membrane to the side, which deflects the hair cell receptors

on either side of the striola

hair cells have opposite preferred directions

otolith organs oriented so all

three axis of head motion detected

holding the head tilted or continuous linear acceleration - pressing gas pedal while driving a car will continuously

deflect hair cells in otolith organ

tilt/acceleration in the opposite direction will

deflect hair cells in the anti preferred direction - reducing the firing rate

signals from the otolith organs are

ambiguous on their own

somatogravic illusion

pilots mistake fast forward acceleration with tilting upwards - so they correct it by lowering the plane

vestibulo-ocular reflex

stabilizes eyes in space when head is moved around

head rotates then the eyes counter rotate to stay in a fixed position

horizontal vor

rotating head left and right

vertical vor

tilting head forward and backward

torsional vor

rolling head side to side

hair cells within ampullae on either side of the head have

opposite preferred directions of head rotation

head rotation to the left increasing fire rates in __ ampulla afferents and decreases firing rates in __ ampulla afferents

left, right

eye muscles when u turn head to the left

increase left medial recuts and right lateral rectus

decrease left lateral recuts and right medual rectus

vestibulo-collic reflex

stabilizes the head in space when moving around

head is tilted, neck counter rotates to keep head fixed in position

coronal VCR

tilting head side to side

tilting the head to the left increases firing rate of what and decrease firing rate of what - coronal VCR

increase firing rate in the medial portion of the left utricle

decrease firing rate in the medial portion of the right utricle

leads to muscle contraction of the lateral flexor motor neurons on the right side of the head to bring head vertical

afferents on the lateral side of the utricle connect to

the ipsilateral neck

efferent neurons from the medial vestibular nucleus project down the

ventral medial portion of the brainstem and into the cervical spinal cord to control neck muscle bilaterally - the VCR

efferent neurons from the lateral vestibular nucleus project down the

lateral vestibular tract to ventral horns in the thoracic, lumbar and sacral spinal segements to activate axial/proximal muscles for controlling posture and balance

vestibular reflexes that control posture and balance are called

vestibular spinal reflexes

the cerebellum receives input from the vestibular nucleus and projects back to the

vestibular nucleus to influence the vestibular spinal pathways

the cerebellum is involved in adaptively fine tuning

VOR, VCR, VSR based on changes in sensory function

• damage to vestibular organs

• age related hair cell receptor loss

• head position

• prism goggles

cerebellum also involved in determining vestibular signals generated from

self motion vs external forces - car

cn v3

vestibulocochlear nerve

there is no single primary vestibular cortex

distributed set of cortical areas in the parietal lobe where neurons are modulated by vestibular inputs

parietoinsular vestibular cortex - PIVC

has neurons that integrate vestibular, visual optic flow, and somatosensory info

• provide a special frame of reference for proprioception and coordinating movement and posture

3a is the ___ region and 2v is

face neck region of s1 and 2v is caudal to this

vestibular head impulse test

test vestibular function by physically rotating the head

nystagmus

eye movements that occur under continuous vestibular stimulation

slow phase in the counter direction of head rotation (vor)

then when eye reaches the end of rom, flicks back quickly - fast phase

catch up saccades to the left when

head is rotate to the right - right side vor abnormality

caloric vestibular testing

warm water should activate then cold water should inhibit

rotational/translational vestibular testing

in a robotic chair that can rotate them in different planes

they need to determine which direction they moved - no eye/air pressure cues

measure changes in perceptual sensitivity - age

can also evoke VOR’s

electrical vestibular stimulation - evs

low intensity current delivered thru the skill and stimulates vestibular afferents directly, artifical/virtual vestibular sense of motion

the positive and negatie ends of the stimulator can be flipped bu the only the fly hardware

afferents on the positive side of EVS

decrease firing rates

afferents on the negative side of EVS

increase firing rates

balance response testing EVS

subjects sway towards positive electode - corrective balance response from the EVS

perceptual sensitivity testing EVS

it feels like you are rotating to the negative side

EVC causes a physical perturbation to balance control thru the

VSR pathway - sway to the positive side

craniocentric

direction of evs evoked balance response depends on head position