Control of movement. Spinal control of movement.
Movement in the human body is controlled by a complex interplay of the nervous system and the muscular system. It involves a hierarchical organization, from the motor cortex in the brain, down to the spinal cord, and finally to the muscles.
Levels of Motor Control
- Cortical Level (Motor Cortex): Planning, initiation, and execution of voluntary movements.
- Subcortical Level (Basal Ganglia and Cerebellum): Refinement and coordination of movements.
- Brainstem Level: Control of posture, balance, and muscle tone.
- Spinal Cord Level: Reflexes, basic motor patterns, and the final common pathway for all motor output.
Types of Movement
- Tonic Movements: Long-lasting contractions that maintain posture and equilibrium, primarily involving axial muscles (trunk and head).
- Phasic Movements: Rapid, wide-ranging contractions used for locomotion and voluntary actions, primarily involving distal muscles (limbs).
Muscle Fiber Types
- Extrafusal Fibers: Responsible for generating force during muscle contraction.
- Innervated by α-motoneurons.
- Constitute the majority of skeletal muscle mass.
- Intrafusal Fibers: Specialized fibers within muscle spindles, sensory organs that detect changes in muscle length.
- Innervated by γ-motoneurons.
- Types:
- Nuclear Bag Fibers: Nuclei clustered in a central "bag."
- Nuclear Chain Fibers: Nuclei arranged in rows.