Lecture 11: Posture and Balance Flashcards
what is Centre of mass (CoM)
point where the mass of the body is equally distributed
what is Base of support (BoS)
area of the body in contact with the support surface
what is Centre of pressure (CoP)
Center of distribution of force applied to the supporting surface
Moves continuously around the CoM to keep it within the BoS (hearding dog)
what is postural control
umbrella term
Controlling body position for orientation and stability
what is postural orientation
ability to maintain an appropriate position
(lean forward when walking up hill)
what is postural stability/balance
Ability to control centre of mass (COM) relative to gravity and base of support (BOS)
what is the stability if a person is sitting reading a book
large base of support
what is the stability of a person standing to read
more demands than sitting because base of support is smaller
what is the stability of a person walking and looking forward
centre of mass does not stay within base of support, so there is a continuous state of imbalance
do postural control requirements change wit the task and environment
yes
3 main sources of sensory input to the CNS
somatosensory (70%)
vestibular system (20%)
Vision (10%)
when learning a new skill, do we rely more on somatosensory input or vision for postural stability
vision
what are the 2 parts of Vestibular Apparatus
bony labyrinth
membranous labyrinth
what is the membranous labyrinth
Suspended within bony labyrinth
Filled with fluid (endolymph)
Sensory receptors (hair cells) that tell us where our head has moved
what are the Semicircular Canals
3 perpendicular bones in each ear
has cupula (gelatinous mass) with hair bundles inside
what displaces hair cells in ear
Angular acceleration which
depolarizes all hair cells together
what is the purpose of the semicircular canals
stabilize vision during head turns
what are the names of the 3 Semicircular Canals and how are they positioned
anterior(superior), posterior, and horizontal canals
Oriented at 90 degrees to one another
anterior and posterior canals are 45 degrees from midline
what is the counter balanced design
Each canal works with a partner on the opposite side
Canals activate more strongly in response to movement in a particular plane
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 are the horizontal canals sensitive to
Rotation in the transverse plane (head turns)
what 2 movements are the Superior/anterior and posterior canals sensitive to
Movement in sagittal plane (nodding)
Movement in the coronal plane (side-bending)
in general, the direction of head movement corresponds to what in canals
an increase in the activity of that canal
how are semicircular canals sensitive to angular acceleration
Frequency of action potentials increases with higher acceleration
what are the 2 types of otolith organs
Saccule and Utricle
what are otolith organs
One utricle and saccule on each side that mirror the other side
Each contain a sensory epithelium (macula)
topped by crystals (otoconia)
what type of movement are otolith organs sensitive to
linear movements and static head tilts
what is the orientation of the utricle and what is it responsive to
more horizontal
responsive to horizontal movement (side bending, lateral displacement)
what is the orientation of the Saccule and what is it responsive to
more vertical
responsive to vertical movement (up/down, forward/backward)
how are hair cells in otoliths orientated and what movement are they sensitive to
Hair cells oriented in different directions
On opposite sides of each macula, hair cells are sensitive to opposite motions (half depolarizes)
are otoliths sensitive to acceleration?
no. they have Tonic or sustained pattern of activation
what 2 things are special about vestibular inputs
They are multisensory (receive visual and vestibular input)
vestibular nuclei provide very fast compensatory eye and head movements
why is it important that the vestibular pathways are multi sensory
- Essential for postural control and control of eye movements
what is the Medial longitudina lfasciculus (MLF)
connection between vestibular and visual systems
tells the eyes which way they should move
Involved in the vestibular- ocular reflex (VOR)
what is the vestibular- ocular reflex (VOR)
as head turns to the right while looking at something,
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 Involved in the vestibular- ocular reflex (VOR)
Keep eyes on target while head is moving
what are Vestibulospinal Tracts
Involved in the control of postural orientation and stability
Vestibular nuclei give rise to the lateral and medial vestibulospinal tracts
what is the Medial Vestibulospinal Tract
Arises from medial vestibular nucleus
Descends bilaterally in spinal cord
Regulates head/neck position
which reflex is the medial vestibulospinal tract involved with
Vestibular cervical reflex
Moves head in opposite direction of motion
when falling forward, neck extends to protect neck
what is the Lateral Vestibulospinal Tract
Arises from lateral vestibular nuclei
Controls proximal extensor muscle tone for maintenance of posture in legs
what reflex is involved with the Lateral Vestibulospinal Tract
Vestibular spinal reflex (VSR)
Body flexes in opposite direction of motion
if our body is pushed to the right, we lean to the left to come upright
what does the cerebellum do
Cerebellum provides input to medial and lateral vestibular nuclei
what 2 things does the cerebellum distinguish between
Motions detected by otoliths and semicircular canals
Active vs passive movements
what is the Vestibular Cortical System
vestibular information ascends bilaterally to the thalamus, then to the parietal cortex and insula
generates a head-in-space picture
are vestibular and visual systems are matched to one another
yes
what is Physiological vertigo
conflict between sensory systems (motion sickness)
what is pathological vertigo
caused by a sudden imbalance of vestibular signals
what is Spontaneous Nystagmus
movement of the eyes without stimulus.
what is Benign Paroxysmal Positional Vertigo (BPPV)
Most common cause of vertigo
Displacement of otoconia from the otoliths into the posterior semicircular canal
Signals to the brain that movement is occurring despite no movement
what is the Epley Maneuver
Treatment of posterior canal BPPV
Displaces the otoconia back into the otoliths using gravity
what is the feedforward mechanism
anticipatory postural adjustments in anticipation of postural instability
what is the feedback mechanism
corrective postural control strategies in response to unanticipated postural instability
what are the 3 types of balance control
Static/Steady State balance
Anticipatory/Proactive balance
Reactive balance
what is Static/Steady State balance
Ability to control the COM relative to the BOS in predictable and unchanging conditions
(standing on leg, keeping self balanced)
what is Anticipatory/Proactive balance
Ability to activate muscles for balance in advance of potentially destabilizing voluntary movements (ie. picking up a box)
- Using feedforward mechanisms
what is Reactive balance
Ability to recover a stable position following an unexpected perturbation
- Using feedback mechanisms
(bus hits the breaks and we need to rebalance)
why is Static and dynamic balance really a continuum
when we are “static” we still sway so we are still moving
what are the 2 postural stability functions
anticipatory (minimize upcoming issues - feedforward)
reactive (correct errors - feedback)
what is Anticipatory Postural Adjustment
Activation of postural muscles before execution of voluntary goal
why is Reticulospinal Tract important for postural control
Bilateral terminations
Postural control to support skilled/coordinated movements
Muscle tone
what is ankle strategy
Activated during small perturbations and firm surfaces
Rely heavily on somatosensory input
Distal muscles activated first
what is the hip strategy
(standing on balance beam)
Activated during larger or faster perturbations
Rely more on vestibular and visual inputs
Proximal muscles activated first
what is change in support strategies
Moving the limbs to change the BOS
Humans can adapt by shifting from one strategy to another
reaching or stepping
what does abnormal postural control look like
Increased sway
slower anticipatory control
Increased reliance on hip and stepping strategies
how does cognition contribute to abnormal postural control in people with strokes
Reaction times increase with increasing postural control demands
