Posture and Balance Flashcards
what is CoM?
point where the
mass of the body is equally distributed
what is BoS?
area of the body in
contact with the support surfac
what is CoP?
Center of
distribution of force applied to the
supporting surfac
what is postural control?
Controlling body position in space
for dual purpose of orientation
and stability
what is postural orientation?
Ability to maintain an appropriate
position of the whole body with
respect to the environment and
task
what is postural stability?
Ability to control centre of mass
(COM) relative to gravity and base
of support (BOS) during
perturbations or motor tasks
what is the definition of balance?
Ability to control the centre of
mass relative to gravity and the
base of support
what are the 3 main sources of sensory input to the CNS?
vestibular system - 20%
visual system - 10%
Somatosensory system - 70%
what makes up the boney labyrinth?
Auditory: cochlea
vestibular: otolith organs, semicircular canals
what part of the inner ear allows us to hear?
cochlea
what are the two parts of the otolith organs?
utricule and saccule
what is the fluid that fills the membranous labyrinth called?
endolymph
what are the sensory receptors within the membranous labyrinth?
hair cells
what does each semicircular canal contain?
an ampulla
what is contained within each ampulla?
a cupula (gelatinous mass)
where would you find the hair cells within the semicircular canals?
within the cupula
what will displace the hair cells within the canals?
angular acceleration rotates th egel
how are the hair cells depolarized in the semicircular canals?
all hair cells depolarize together
what is the purpose of the semicircular canals?
stabilize vision during head turns
what are the different semicircular canals?
anterior, posterior, horizontal
how are the semicircular canals oriented to each other?
Oriented at 90 degrees to
one another
how are the anterior and posterior semicircular canals oriented to midline?
Superior and posterior
canals are 45 degrees
from midline
how is there a counter balance design to the semicircular canals?
Each canal works with a partner on the opposite side
Canals activate more strongly in response to movement in a particular plane
what happens to firing when we move our head to a particular side?
We increase activity in the semicircular canal on the side we are moving toward and decrease activity the side we are moving away from
what movement is the horizontal semicircular canal sensitive to?
Rotation in the transverse plane ie. head turns
what movement are the anterior/posterior semicircular canals sensitive to?
Movement in sagittal plane ie. nodding head
Movement in the coronal plane ie. side- bending
what happens to the frequency of action potentials in relation to acceleration?
Frequency of action potentials increases with higher acceleration
how many utricle and saccules are on each side?
One utricle and saccule on each side
do the saccules or utricules contain a sensory epithelium?
both
what is the sensory epithelium of a utricule and saccule called?
macula
what does the macula contain?
hair cells enclosed by a gelatinous mass topped by crystals
what is the crystal layer of the sensory epithelium called?
otoconia
what are the utricules and saccules sensitive to?
linear movements and static head tilts
what is the macular orientation of the urticule like?
more horizontal, meaning it is more responsive to horizontal movement like side bending, lateral displacement
what is the macular orientation of the saccule like?
more vertical meaning it is more responsive to vertical movement like up-down, forward/backward movement
what is the hair cell orientation in the utricule and saccule?
they are oriented in different directions, so on opposite sides of each macula, hair cells
are sensitive to opposite motions
why are the vestibular pathways special?
- They are multisensory (receive
visual and vestibular input)
* Essential for postural control
and control of eye movements - Vestibular nuclei provide very
fast compensatory eye and head
movements
what is the function of the medial longitudinal fasciculus (MLF)?
tells the eyes which way
they should move via connections
with cranial nerves
what reflex is the medial longitudinal fasciculus involved with?
vestibular-ocular reflex (VOR)
what is an example of the vestibular-ocular reflex (VOR)?
As head turns to right:
Right horizontal semicircular canal is
active; left horizontal semicircular canal
is inhibited
Eye musculature responsible for moving
eyes to left are activated
Eye musculature responsible for moving
eyes to the right are inhibited
what is the function of the vestibular-ocular reflex (VOR)?
Keep eyes on target while head is moving
what is the vestibulospinal tract involved in?
the control of postural orientation and stabilit
what tracts does the vestibular nuceli give rise to?
medial and lateral vestibulospinal tracts
where does the medial vestibulospinal tract arise from?
medial vestibular nucleus
how does the medial vestibulospinal tract descend?
bilaterally in spinal cord
what does the medial vestibulospinal tract regulate?
head/neck position
what is the vestibular cervical reflex? (VCR)
Moves head in opposite direction
of motion
where does the lateral vestibulospinal tract arise from?
lateral vestibular nuclei
what does the lateral vestibulospinal tract control?
proximal extensor muscle tone for
maintenance of posture
* Particularly lower limbs
what is the vestibular spinal reflex (VSR)?
Body flexes in opposite direction of motion
what does the cerebellum provide input to?
medial and lateral vestibular
nuclei
what does the cerebellum distinguish between?
Motions detected by otoliths
and semicircular canals
Active vs passive
movements
where does the vestibular cortical system ascend from?
bilaterally from vestibular nuclei to the
ventral posterior nucleus of
the Thalamus
where does the vestibular cortical system go to
Multiple cortical areas
* Parietal cortex and insula
what does the vestibular cortical system generate?
a head-in-space picture
what system is the vestibular system matched to?
visual system
why does physiological vertigo occur?
because there is a conflict between sensory
systems
why does pathological vertigo occur?
a sudden imbalance of vestibular signals
due to a lesion in the vestibular system
what is the most common form of vertigo?
Benign Paroxysmal Positional Vertigo
(BPPV)
what causes Benign Paroxysmal Positional Vertigo (BPPV)?
Displacement of otoconia from
the otoliths into the semicircular
canal
what happens when there is a crystal thats gets into the semicircular canals?
Signals to the brain that movement
is occurring despite no movement
what canal does a displaced crystal typically wind up in?
90% of the time, the posterior
canal
what is the name of the maneuver to put the crystal back in place?
Epley maneuver (uses gravity)
what is the feedforward mechanism?
anticipatory postural adjustments executed in anticipation of postural instability
what is the feedback mechanism?
corrective postural control strategies in response to unexpected postural instability
what is static/steady state balance?
our ability to control our center of mass relative to our base of support in predictable and unchanging environments
what is anticipatory/proactive balance?
our ability to activate muscles for balance in advance of potentially destabilizing voluntary movements (primarily using feedforward mechanisms)
what is reactive balance?
our ability to recover our stability after an unexpected perturbation (using feedback machanisms)
when is the ankle strategy activated?
small perturbations on a firm base of support
what does the ankle strategy rely heavily on?
somatosensory inputs
what muscles are activated first for the ankle strategy?
distal muscles
when is the hip strategy activated?
during larger or faster perturbations or when on compliant surfaces or smaller BoS
what does the hip strategy rely heavily on?
vestibular and visual inputs
what muslces are activated first in the hip strategy?
proximal muscles then distal muscles
what are some change in support strategies?
moving the limbs to change the BoS
shifting from one strategy to another or using a combination of strategies
