Overview
This lecture explains how muscles generate force by contracting sarcomeres and varying the number of motor units recruited for different levels of tension and force.
Muscle Structure and Function
- Muscles are made of muscle fibers, which contain myofibrils composed of sarcomeres.
- The sarcomere is the functional unit of muscle, responsible for muscle contraction and shortening.
- Muscle contraction creates tension, allowing the body to perform work.
Motor Units and Force Production
- Each muscle fiber is innervated by one motor neuron, but one motor neuron can control multiple muscle fibers.
- A motor unit is defined as all muscle fibers innervated by the same motor neuron.
- The number of motor units recruited determines the amount of muscle tension and force produced.
- Light tasks require fewer motor units, while heavier tasks require recruitment of more motor units.
- Motor units can rotate (alternate activity) to prevent fatigue during prolonged or light activities.
Key Terms & Definitions
- Sarcomere — the basic contractile unit of muscle fiber responsible for contraction.
- Motor neuron — a nerve cell that stimulates muscle fibers to contract.
- Motor unit — a group of muscle fibers innervated by a single motor neuron.
Action Items / Next Steps
- Review the definitions of sarcomere, motor neuron, and motor unit.
- Practice identifying how different tasks might recruit varying numbers of motor units.