motor

Motor Control Overview

  • Focus: Understanding motor control mechanisms in human movement

Types of Movements

  • Reflexes: Simple and quick muscle activations (e.g., eye blinks, hiccups)

  • Acts (Action Patterns): Complex and sequential activities (e.g., playing an instrument, writing)

  • Motor Plans: Preset muscle commands that guide movements, crucial for brain function in movement coordination.

Control Mechanisms in Movement

Speed and Accuracy

  • Open-loop Control:

    • Maximizes speed without external feedback.

    • Ballistic movements occur rapidly regardless of sensory input.

  • Closed-loop Control:

    • Maximizes accuracy with continuous sensory feedback.

    • Utilizes ramp movements that are smooth and maintained through guidance.

Hierarchy of Motor Control Systems

  • Skeletal Muscles: Basic units powering movement.

  • Spinal Cord: Controls skeletal muscle movements.

  • Brainstem: Integrates motor commands from the higher brain.

  • Cortex Processes:

    • Primary Motor Cortex: Initiates movement commands.

    • Nonprimary Motor Cortex: Manages additional processing.

  • Cerebellum & Basal Ganglia: Fine-tunes motor commands for precision.

Muscle Functionality

  • Antagonistic Muscles: E.g., biceps and triceps. Balance at rest between flexor and extensor muscles.

  • Action Potentials: Electrical signals that travel from motoneurons to muscle, prompting contraction.

Neuromuscular Junctions

  • Site where motor neuron terminal meets muscle fiber.

  • Acetylcholine (ACh): Neurotransmitter released, facilitating muscle contraction.

Motor Units

  • Defined as a motoneuron's axon and all its target muscle fibers.

  • Smaller innervation ratios:

    • Fine motor skills (e.g., hand movements) have lower ratios (e.g., 1:3).

Proprioception

  • Mechanism allowing awareness of body position and movement.

  • Muscle Spindles: Detect muscle stretch.

  • Golgi Tendon Organs: React to muscle contraction.

Stretch Reflex Mechanism

  1. Muscle is stretched -> Excitation of muscle spindle -> Muscle contraction to maintain length.

  2. Involvement of afferent and efferent pathways ensures stable posture and balance.

Disorders of Movement Control

Spasticity

  • Results from impaired stretch reflex control where normal cortical inhibition is lost, leading to exaggerated reflexes.

Pyramidal vs. Extrapyramidal Systems

  • Pyramidal System: Involves the primary motor cortex; responsible for direct voluntary control.

  • Extrapyramidal System: Include basal ganglia and cerebellum; modulates and fine-tunes movements.

Learning and Motor Skills

  • The motor cortex adapts with learning, such as music training which leads to cortical expansion.

Central Pattern Generators

  • Neural circuits creating rhythmic patterns of movement (e.g., walking).

Higher Level Motor Disorders

  • Apraxia: Difficulty in planning movements without paralysis.

  • Parkinson's Disease: Characterized by bradykinesia, resting tremor, and postural instability.

Other Neuromuscular Disorders

  • Myopathy: Primarily muscle disease affecting the muscle fibers.

  • Muscular Dystrophy: Due to lack of dystrophin protein, leading to muscle degeneration.

  • Myasthenia Gravis: Autoimmune disorder affecting ACh receptors leading to muscle weakness.

  • Polio: Viral infection leading to motoneuron destruction.

Ataxia and Other Movement Disorders

  • Issues related to cerebellar damage leading to impaired motor control.

Summary of Motor System Damage Effects

  • Different types of damage can cause distinct motor impairments, from weakness to severe movement dysfunctions.