Week 9 Flashcards
*What is balance?
Quiet standing involves keeping the centre of
mass (COM) within the base of support (BOS)
*Centre of Mass & Pressure?
Centre of Pressure (COP) actively oscillates forward/back to maintain
the Centre of Mass (COM) within the limits of stability.
*Active Modulation?
Passive ankle stiffness alone cannot maintain balance; active muscle control is required.
What is Motion parallax?
Objects appear to move relative to each other when we sway – provides more information
Visual vection?
A false sense of motion induced by a moving scene
*Perturbing visual input? What does it look like?
Subjects sway in the direction of visual scene movement
The brain interprets forward scene motion as backward body motion
Therefore produces a compensatory forward response
Visual perturbation causes initial sway in the direction of visual motion (~1s after onset), followed by corrective sway (2-3s later). Best responses occur with slow, low-frequency motion (<0.1Hz, <5°/s). Responses habituate quickly and are influenced by expectation and cognition. The brain interprets visual stimuli by distinguishing between object- and self-motion using prior knowledge
Effect of predictability on visual response?
No response as body is aware from prior experience or expectations
Swing-stance pattern?
Alternating pattern of swing-stance
Flexors active during swing (e.g. TA, hamstrings, Hip flexors)
Extensors active during stance (e.g. triceps surae, quadriceps, Gluteus)
*Ground reaction forces - walking?
Large vertical force upon heel-strike
Accompanied by a decelerating (backward) shear force (dotted line)
Push-off includes an ACCelerating shear force, accompanied by a secondary vertical force
*Muscle actions of locomotion?
Alternating eccentric and concentric contractions control locomotion.
Eccentric contraction (stance start) brakes motion, while concentric contraction (stance end) provides push-off
*Central Pattern Generators (CPG)?
Spinal networks generate rhythmic locomotor patterns without sensory input.
“Half-centers” of excitatory flexor and extensor neurons alternate activity via mutual inhibition.
Sensory feedback modulates CPG, aiding in phase transitions like swing initiation.
Brain Contributions in locomotion?
Motor cortex: Adjusts for obstacles using visual inputs.
Mesencephalic locomotor region (MLR): Initiates and adjusts gait speed.
Cerebellum/brainstem: Fine-tunes patterns with real-time sensory input.
Special Adaptations of locomotion?
Passive dynamics, such as gravity and limb pendulum action, reduce energy costs
*Purpose of Eye Movements?
Maintain a clear image/bring points of interest on the fovea.
Avoid visual blur and track objects effectively.
*Types of Eye Movements?
Fast movements:
Saccades: Quick jumps to reposition focus (up to 900°/s, ~3 per second).
Resetting movements: During Vestibulo-Ocular Reflex (VOR) and Optokinetic Reflex (OKR).
Slow movements:
VOR: Stabilizes vision during head movement.
OKR: Visual stabilization during prolonged motion.
Smooth pursuit: Tracks moving objects using predictive mechanisms.
Vergence: Aligns both eyes for depth perception
Control and Adaptation - Eye movements?
Saccades are ballistic and can be reflexive or voluntary.
VOR adapts to changes (e.g., stronger glasses) but is impaired in vestibular dysfunction or cerebellar diseases
*Methods of Measurement of eye movements?
Electrooculography (EOG): Tracks electric potential changes.
Infrared reflectance: Monitors eye position using
IR beams.
Scleral coil: Accurate but invasive.
Video-oculography (VOG): Tracks pupil and gaze with software
*Applications and Observations of eye movements?
Saccades reveal motor prediction in activities like walking or sports (e.g., cricket batting).
Eye movements in tasks like tea-making or walking predict upcoming actions.
Action observation involves predictive gaze, aligning observed actions with motor representations.
Common Eye movement Disorders?
Absent VOR: Leads to oscillopsia (blurry vision).
Dysmetric saccades: Visual issues in cerebellar dysfunction
*What does a locomotor pattern involve?
A locomotor pattern involves rhythmic muscle activity and characteristic ground reaction forces, enabling efficient propulsion, stability, and balance during movement
*Where does the basic locomotor pattern come from?
It comes from the spinal cord, where central pattern generators (CPGs) produce rhythmic muscle activity for movements like walking, even without brain input.
*What role do supraspinal areas play in locomotion?
Supraspinal areas initiate, stop, and fine-tune locomotion by modulating spinal cord activity for adaptive and goal-directed movements.
*How does sensory feedback influence locomotor patterns?
Sensory feedback adjusts locomotor patterns to maintain stability, adapt to changes, and enhance movement efficiency
*How do saccades contribute to motor control?
Saccades provide predictive information, aiding in anticipation and adaptation during movements like locomotion.
