Overview
This lecture covers the types of muscle tissue, their characteristics, and focuses on the mechanism of skeletal muscle contraction, highlighting the sliding-filament model and its regulation.
Types of Muscle Tissue
- Three types: cardiac, smooth, and skeletal muscle tissue.
- Cardiac muscle is found in the heart, is striated, branched, often has one or two nuclei, contains intercalated discs, and is involuntary.
- Smooth muscle is non-striated, spindle-shaped, single nucleus per cell, found in organs and vessels, and is involuntary.
- Skeletal muscle is striated, long cylindrical multinucleated fibers, attaches to bones or skin, and is under voluntary control.
Muscle Tissue Characteristics
- Muscle tissue has extensibility (can stretch), elasticity (returns to original shape), excitability (responds to stimuli), and contractility (can contract).
- All muscles contract, but details differ between tissue types.
Skeletal Muscle Structure and Naming
- Skeletal muscles are named by location, shape, and often use Latin or Greek roots.
- Muscle origin attaches to fixed bone, insertion attaches to moveable bone.
- Agonist (prime mover) performs the action; antagonist reverses it.
Skeletal Muscle Cellular Structure
- Skeletal muscles are made of large muscle fibers containing multiple myofibrils.
- Myofibrils are composed of repeating sarcomeres, responsible for the striated appearance.
- Sarcomeres contain thin filaments (actin) and thick filaments (myosin).
Sliding-Filament Model of Contraction
- Muscle contraction occurs when sarcomeres shorten, not by filaments shortening, but by sliding past each other.
- Myosin heads hydrolyze ATP to bind actin forming a cross bridge, then release ADP and phosphate, causing a power stroke.
- New ATP binding allows myosin detachment, essential for relaxation.
Regulation of Muscle Contraction
- Tropomyosin blocks myosin-binding sites on actin; troponin complex helps regulate this blockage.
- Neuron stimulation releases calcium ions, which bind troponin, shifting tropomyosin and exposing binding sites.
- Without ATP, muscle remains contracted (rigor mortis).
Key Terms & Definitions
- Sarcomere — basic contractile unit of muscle fiber, bordered by Z lines.
- Actin — protein forming thin filaments in sarcomeres.
- Myosin — protein forming thick filaments, responsible for power stroke.
- ATP — energy molecule required for myosin-actin detachment.
- Tropomyosin — protein that blocks myosin-binding sites on actin.
- Troponin — regulatory protein complex that binds calcium and moves tropomyosin.
- Agonist — main muscle responsible for a movement.
- Antagonist — muscle that performs the opposite movement.
Action Items / Next Steps
- Review diagrams of muscle types and sarcomere structure.
- Practice identifying skeletal muscle origins, insertions, agonists, and antagonists.
- Explore additional resources to learn detailed muscle names and locations.