Week 9

Question 1

*What is balance?

Answer 1

Quiet standing involves keeping the centre of
mass (COM) within the base of support (BOS)

Question 2

*Centre of Mass & Pressure?

Answer 2

Centre of Pressure (COP) actively oscillates forward/back to maintain
the Centre of Mass (COM) within the limits of stability.

Question 3

*What is sway? Why do we sway?

Answer 3

1) Sensory estimation – an imperfect process with
sensor noise.

2) Motor output – also an imperfect process.

3) External/internal perturbations. E.g. Breathing,
wind, being pushed etc.

Sway mainly occurs at the ankle joint, with calf muscles preventing forward falls.

Removing visual information increases sway

Question 4

*Active Modulation?

Answer 4

Passive ankle stiffness alone cannot maintain balance; active muscle control is required.

Question 5

What is Motion parallax?

Answer 5

Objects appear to move relative to each other when we sway – provides more information

Question 6

Visual vection?

Answer 6

A false sense of motion induced by a moving
scene

Question 7

*Perturbing visual input? What does it look like?

Answer 7

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

Question 8

Effect of predictability on visual response?

Answer 8

No response as body is aware from prior experience or expectations

Question 9

Swing-stance pattern?

Answer 9

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)

Question 10

*Ground reaction forces - walking?

Answer 10

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

Question 11

*Muscle actions of locomotion?

Answer 11

Alternating eccentric and concentric contractions control locomotion.

Eccentric contraction (stance start) brakes motion, while concentric contraction (stance end) provides push-off

Question 12

*Central Pattern Generators (CPG)?

Answer 12

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.

Question 13

Brain Contributions in locomotion?

Answer 13

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.

Question 14

Special Adaptations of locomotion?

Answer 14

Passive dynamics, such as gravity and limb pendulum action, reduce energy costs

Question 15

*Purpose of Eye Movements?

Answer 15

Maintain a clear image/bring points of interest on the fovea.

Avoid visual blur and track objects effectively.

Question 16

*Types of Eye Movements?

Answer 16

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

Question 17

Control and Adaptation - Eye movements?

Answer 17

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

Question 18

*Methods of Measurement of eye movements?

Answer 18

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

Question 19

*Applications and Observations of eye movements?

Answer 19

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.

Question 20

Common Eye movement Disorders?

Answer 20

Absent VOR: Leads to oscillopsia (blurry vision).

Dysmetric saccades: Visual issues in cerebellar dysfunction

Question 21

*What does a locomotor pattern involve?

Answer 21

A locomotor pattern involves rhythmic muscle activity and characteristic ground reaction forces, enabling efficient propulsion, stability, and balance during movement

Question 22

*Where does the basic locomotor pattern come from?

Answer 22

It comes from the spinal cord, where central pattern generators (CPGs) produce rhythmic muscle activity for movements like walking, even without brain input.

Question 23

*What role do supraspinal areas play in locomotion?

Answer 23

Supraspinal areas initiate, stop, and fine-tune locomotion by modulating spinal cord activity for adaptive and goal-directed movements.

Question 24

*How does sensory feedback influence locomotor patterns?

Answer 24

Sensory feedback adjusts locomotor patterns to maintain stability, adapt to changes, and enhance movement efficiency

Question 25

*How do saccades contribute to motor control?

Answer 25

Saccades provide predictive information, aiding in anticipation and adaptation during movements like locomotion.