KINES471 weeks 9-10 annotated notes

Control of Vertical Posture

Vertical Posture is Mechanically Unstable

  • Center of Mass (COM):
      - High center of mass contributes to instability.

  • Multiple joints increase complexity and potential for instability.

  • Small support area exacerbates mechanical instability.

Postural Sway

  • Definition: COM or Center of Pressure (COP) spontaneous displacement.
      - Graphical representation notes varying metrics for COP and COM displacement over time, expressed in mm.

  • Notable Parameters:
      - Sway patterns can be analyzed through time intervals (seconds).

Impact of Eyes Open vs. Closed on Postural Sway

  • Sway is greater with eyes closed, indicating reliance on visual input for balance.
      - Effectively illustrated through measured displacement in mm under conditions of eyes open and closed.

Sway and Postural Stability

  • Distinction Between Sway and Stability:
      - Patients with Parkinson's disease may exhibit reduced sway but have highly unstable posture.
      - In contrast, sway often increases in postural disorders (even mild, such as in healthy elderly).
      - Example of stable motion: A metronome exhibits large sway but is mechanically stable.

Factors Influencing Postural Sway

  • Increases in postural sway during:
      - Eyes closed condition (loss of visual reference).
      - Standing on a narrow support surface (but not excessively narrow).
      - Aging and certain disorders will exacerbate sway.

  • Decreases in postural sway when:
      - Light finger touch provided to any body part.
      - Holding an object connected to the external world.

Components of Postural Sway

  • Sway is considered as a combination of:
      - Rambling:
        - Describes interpolation of points during which horizontal force is zero.
        - Reflects instantaneous equilibrium points, linking to the Equilibrium Point Hypothesis.   - Trembling:
        - Relates to mechanical properties of effectors and reflexes; influenced by muscular tension.

  • Key finding: Trembling correlates with horizontal force, while rambling does not.

Perception-Action Coupling

  • Example: Visual field motion affects body sway; when viewing an animated screen, movement towards the subject prompts backwards sway.

Reference Frame for Postural Maintenance

  • A stable posture requires a reference vertical.

  • Noteworthy: Light touch on the body reduces sway, influencing the sensitivity of postural responses.

Vestibilular Apparatus

  • Historical Note: Alessandro Volta experimented with a battery applied to the ears, resulting in sensations of environmental motion.

  • Podokinetic effect: Imbalance felt post-marching on a rotating platform.

  • Impact of long-term standing on a slope observed in later level surfaces.

Anatomical Components of the Vestibular System

  • Semi-Circular Canals: Sensitive to angular head acceleration.

  • Otoliths: Sensitive to linear head acceleration.

  • Innervation by the eighth cranial nerve via Scarpa’s ganglion connecting head position to postural adjustments.

Vestibular Nuclei

  • Structure: Input and Output Functions

  • Deiters’ Nucleus: Facilitates leg muscle activity through vestibular-spinal pathways.

  • Inferior Nucleus: Engages neck muscle control.

  • Medial Nucleus: Provides dynamic control to ocular and postural adjustments.

Control Theory Approaches

  • Postural control model functions under the assumption that balance relies on sensory and neuromuscular inputs.

  • Equation showing relationship of balance through various systems:
      - BS=BF+SSBS = BF + SS
      - Where BS is balance state, BF is feedback from the environment, and SS represents sensory signals.

Inverted Pendulum Model for Posture

  • Depicts only one joint (ankle) managing torque.

  • Equation defining torque: T=k(a−a0)T = k(a - a_0)
      - Key Understanding: This model only accounts for trembling, not rambling, leading to its limited applicability.

Movement-Posture Paradox

  • Observation: Voluntary sway is coupled with minimal posture-stabilizing reactions, exemplified in large reactions when shifting towards a leaning position.

Postural Control Mechanisms

  • Deviations are influenced by external forces and muscle reflex properties.

  • Categories of reactions with associated latencies:
      - Anticipatory Postural Adjustments (APAs): < 0 ms (pre-perturbation)
      - Monosynaptic Reflex (30 ms, poorly controlled)
      - Polysynaptic Reflex (50 ms, low gain)
      - Pre-programmed Reactions (70 ms, approximate corrections)
      - Voluntary Actions (150 ms, late responses)

Anticipatory Postural Adjustments (APAs)

  • Initiated during rapid arm movements, leading to postural perturbation through muscle activation.

  • Timing, magnitude of generated torques crucial to maintain balance against internal forces.

Effects of Touch and Grasp on APAs

  • Touch prompts immediate adjustments, while grasping alters posture based on action demands.

  • Influential factors include magnitude, timing, and direction of perturbation.

Summary of Postural Control

  • Key processes include:
      - Shift in equilibrium trajectory (rambling) and trembling due to peripheral influences.
      - Stages preceding actions include:
        - Anticipatory Postural Adjustments (APAs) for future perturbations.
        - Early Postural Adjustments (not APAs) made to facilitate planned actions.

Control of Locomotion

Types of Gait

  • Galloping

  • Walking

  • Trotting

  • Stable Dynamics During Ambulation: Emphasizing stabilization in the anteroposterior (AP) direction while highlighting instability in the mediolateral (ML) direction.

Stability During Gait

  • Analysis of dynamic stability and the role of synergies in determining foot trajectory.{"type":"object"}

Locomotion Dynamics

  • Cerebellum, spinal cord, and the role of the central nervous system (CNS) in regulating locomotion.

  • Mechanisms of locomotion include the mesencephalic locomotor region influence over gait patterns in response to varying stimulation.

Central Pattern Generators (CPGs)

  • Concept: Neurological structures allowing rhythmic activity patterns for locomotion.
      - CPGs can adapt in response to descending signals and sensory feedback, leading to different gaits or rhythmic responses.

Summary of Locomotion Control

  • CPGs are sensitive and can display hierarchical functionality, revealing changes among hindlimb and forelimb responses.

  • Emphasizes the adaptability of locomotor control systems across varying experiences and bodily adjustments.

Conclusion

  • The balance systems rely on both neuromuscular coordination and environmental feedback dynamics to maintain postural stability and facilitate locomotion effectively.