Overview
This lecture introduces the muscular system, covering its general functions, the three types of muscle tissue, and details of muscle structure from whole muscle down to protein filaments.
Functions of the Muscular System
- Muscles enable movement of the skeleton and internal organs (heart, digestion, birth, etc.).
- They help maintain posture and stabilize body position.
- Muscles stabilize joints through tendons and muscle tone (continuous partial contraction).
- Contraction of muscles generates body heat (thermogenesis).
Types of Muscle Tissue
- Three types: skeletal (voluntary movement), cardiac (heart), and smooth muscle (walls of organs, involuntary).
- All muscle types share excitability (respond to stimuli), extensibility (stretch and contract), elasticity (rebound after stretch), and contractility (shorten and exert pull).
- Microscopic appearance, control (voluntary/involuntary), location, and function differ among the types.
- Skeletal muscle typically appears as long, parallel fibers with peripheral nuclei; smooth muscle is more variable in appearance; cardiac muscle is branching.
Muscle Structure Organization
- The whole muscle is covered by epimysium (connective tissue layer).
- Muscles are composed of bundles called fascicles, each surrounded by perimysium.
- Fascicles contain muscle fibers (muscle cells), each wrapped in endomysium.
- Muscle fibers are filled with myofibrils (cylindrical subunits).
- Myofibrils are packed with myofilaments: thin actin and thick myosin protein strands.
Microscopic Structure Details
- Myofibrils do not have a connective tissue sheath but are surrounded by the sarcoplasmic reticulum (important for contraction).
- Myosin (thick filament) and actin (thin filament) interact like a tug-of-war to produce muscle contraction.
Key Terms & Definitions
- Epimysium — outer connective tissue layer surrounding the whole muscle.
- Perimysium — connective tissue wrapping around each fascicle.
- Endomysium — connective tissue surrounding each muscle fiber.
- Fascicle — a bundle of muscle fibers.
- Muscle Fiber — a single muscle cell.
- Myofibril — cylindrical subunit within a muscle fiber, composed of repeating units.
- Myofilament — protein thread within myofibrils (actin and myosin).
- Sarcoplasmic Reticulum — specialized membrane system in muscle cells, involved in contraction.
Action Items / Next Steps
- Review the table and slides from Unit 1 on muscle tissue if any terms or concepts are unclear.
- Watch upcoming videos for details on the mechanism of muscle contraction.