week 10: postural control Flashcards
(10 cards)
Q: Define the terms CoM, CoP, and BoS and explain their relevance to postural control.
A:
CoM (Centre of Mass): The average location of the body’s mass.
CoP (Centre of Pressure): The point where the total pressure of the body is applied to the ground.
BoS (Base of Support): The area beneath the body that provides contact with the ground (e.g., the area around the feet).
Maintaining balance requires keeping the CoM within the BoS, and CoP oscillates around CoM during quiet standing
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Q: What are the two main strategies used in fixed-support postural control?
A:
Ankle strategy: Used for small, slow disturbances; muscle activation from distal to proximal (e.g., tibialis anterior → quads → abs).
Hip strategy: Used for larger, faster perturbations; muscle activation from proximal to distal (e.g., abdominals → quads → shins).
These strategies maintain posture without changing BoS
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Q: Differentiate between reactive and anticipatory (proactive) postural adjustments.
A:
Reactive (feedback): Responds to external disturbances (e.g., swaying when the bus moves suddenly).
Anticipatory (feedforward): Prepares the body in advance for self-initiated movement (e.g., stabilizing before reaching forward)
Q: Describe how the vestibular system contributes to postural control.
A:
Semicircular canals detect angular head motion (rotation).
Otolith organs (utricle & saccule) detect linear acceleration.
This info travels to the vestibular nuclei and activates pathways like:
Medial vestibulospinal tract → neck muscles (vestibulocollic reflex)
Lateral vestibulospinal tract → limb extensors for balance
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Q: What sensory systems contribute to postural control, and how do they interact?
A:
Vision – provides visual motion feedback.
Vestibular system – senses head movement and gravity.
Proprioception – senses joint and muscle position.
Tactile (cutaneous) – detects pressure under feet.
The CNS integrates multisensory input to adjust posture based on reliability and task demands
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Q: What did the Hafström (2002) study show about the role of vision in postural control?
A:
Visual feedback improves stability during balance perturbations.
Eyes open in darkness causes more sway than eyes closed, likely because the CNS expects visual input when eyes are open.
Over time, sway reduces as the CNS adapts to sensory conditions
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Q: How does the body control posture during walking?
A:
Walking = anterior shift of CoM past BoS.
It’s a series of controlled falls, caught by the stepping foot.
People with balance issues may take shorter steps to reduce CoM movement and improve stability
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Q: What is the difference between the vestibulocollic reflex and the cervicocollic reflex?
A:
Vestibulocollic reflex (VCR): Head stabilization in space; triggered by vestibular input via the medial vestibulospinal tract.
Cervicocollic reflex (CCR): Head stabilization relative to the trunk; triggered by neck muscle proprioceptors
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Q: Why is medio-lateral (ML) control harder than anterior-posterior (AP) during walking?
A:
ML control requires more sensory input.
O’Connor & Kuo (2009) showed greater stride variability with ML visual disturbances vs. AP disturbances, indicating more demand on balance systems
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Q: Explain the importance of slow-adapting vs fast-adapting skin receptors in posture.
A:
Slow-adapting (Merkel’s, Ruffini): Detect continuous pressure/stretch → crucial for ongoing postural control.
Fast-adapting (Meissner’s, Pacinian): Detect dynamic change (vibration, movement) → useful for detecting rapid events
