Muscles

Smooth Muscle

Muscle type found in organs, eyes, and blood vessels, characterized by involuntary contraction and one nucleus per cell.

Cardiac Muscle

Muscle type found in the heart, characterized by striations, involuntary contraction, and one nucleus per cell.

Skeletal Muscle

Muscle type found in flesh, characterized by striations, voluntary contraction, and many nuclei per cell.

Skeletal Muscle Function

Roles of skeletal muscle include supporting the body, moving bones, maintaining body temperature, protecting internal organs, and stabilizing joints.

Muscle Contraction

Muscles can only contract, meaning they can only pull and not push, working in pairs that pull in opposing directions.

Sarcolemma

The membrane surrounding a muscle fiber that regulates the entry and exit of materials.

Myofibrils

Organized bundles of myofilaments within muscle fibers responsible for muscle contractions and containing many mitochondria.

Actin

Thin filament in myofilaments, about 5 nm in diameter, consisting of two protein strands wrapped around each other, binding to myosin and causing muscle contractions.

Myosin

Thick filament in myofilaments, about 11 nm in diameter, consisting of two protein strands 10 times longer than actin, binding to actin and causing muscle contractions.

Calcium Ions in Muscle Contraction

Play a crucial role in muscle contraction by binding to troponin, exposing active sites on actin for myosin binding.

Energy for Muscle Contraction

Muscles require ATP for energy, obtained through creatine phosphate breakdown, aerobic cellular respiration, and fermentation.

Muscular Atrophy

Decrease in muscle size due to lack of use, leading to the metabolism of excess muscle tissue to save energy demands.

Muscular Hypertrophy

Increase in muscle size and strength induced by exercise, involving the growth of muscle fibers and adaptation to withstand future stress.

Slow-twitch Muscle Fibers

Muscle fibers that primarily produce energy aerobically, contract slowly, have high endurance, and are rich in myoglobin and mitochondria.

Fast-twitch Muscle Fibers

Muscle fibers that primarily produce energy anaerobically, are rich in glycogen for rapid ATP regeneration, fatigue easily, and have fewer mitochondria and less vascularization.

Fast-twitch Oxidative Muscle Fibers

Intermediate muscle fiber type with characteristics of fast-twitch fibers and high capacity for aerobic ATP production, making them more resistant to fatigue with endurance training.