Lecture 2: posture and balance control Flashcards
Main functions of postural control
- Orientation- adjustment of body and head relative to vertical
- Balance- maintain COG within BOS; generate sufficient posture against gravity
When are people balanced?
when vertical line of gravity from COG is within the BOS
COG moving forward of BOS
- Precursor for walking
* Foot advances to enable dynamic BOS, thus enabling balance
Neural control of posture
- Higher-level planning/ central command
- Central co-ordination
a. Cerebellum- sensory info and modulates activity
b. Basal ganglia- control muscle tone for posture and initiation of movement
c. Midbrain and spinal network mediation - Movement strategies (prep/anticipatory)- feedforward control
- Biomechanical output- BOS and available ROM; power generation
- Central output adjustment (reactive strategies)
Spinal networks involved in posture
- Tectospinal
- Medial reticulospinal
- Vestibulospinal
- Ant. corticospinal
Sensory input involved in central output adjustment
- Vision
- Vestibular
- Proprioceptors
Feed forward v Feed back
- Forward = strategies to cope with expected postural disturbances
- Back= strategies to counteract unexpected disturbances
Use of vision in feedback
- Movement direction and speed
- Cues for judging upright alignment
- Vision dominates vestibular and somatosensory inputs
Use of vestibular system in feedback
- Vestibular apparatus in ear
- Head position relative to gravity
- Head movement
- Maintain gaze stability (vestibular ocular reflex [VOR])
- Vestibular conditions = more sway; can compensate with intact visual and somatosensory
Use of somatosensory system in feedback
- Input from cutaneous receptors
- Muscle spindles and Golgi tendon organs
- Info about weight bearing and relative position of body parts
Control of quiet stance
- Central organization of posture
- Body alignment
- Postural tone
- Ankle strategy > hip strategy
Ankle strategy- perturbed stance
- Muscles around ankle recruited first
- Direction of disturbance does not affect recruitment order
- Used for small perturbations when support surface is firm
Hip strategy- perturbed stance
• Muscles at trunk are activated before thigh and leg
• Large and rapid hip movement
• Restores equilibrium in response to larger and faster perturbations
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Stepping strategy
- When hip and ankle strategies can’t recover
* Rapid movement used to realign BOS under COG
Anticipatory postural reactions
trunk and limb muscles are utilised prior to predicted perturbation to provide postural stability
