Chapter 6 - The Muscular System

Tendon

A band of connective tissue that connects muscle to bone.

Fascicles

A bundle of skeletal muscle fibers (cells) that forms a part of a muscle. Each fascicle is wrapped in its own connective tissue sheath.

Myofilament

A contractile protein within muscle cells. There are two types: myosin (thick) filaments and actin (thin) filaments.

Striated Muscle

A contractile tissue. On of three types of muscle in the body. These cells are cylindrical, have many nuclei, and have stripes (striations). It provides for conscious, voluntary control over contraction. It attaches to bones and forms the muscles of the body. Also called skeletal muscle.

Sliding Filament Model

A model of the mechanism of muscle contraction in which the myofilaments actin and myosin slide across one another, causing a sarcomere to shorten. When enough sarcomeres shorten, the muscle contracts.

Motor Unit

A motor neuron and all the muscle fibers (cells) it stimulates.

Muscle Fibers

A muscle cell.

Summation

A phenomenon that results when a muscle is stimulated to contract before it has time to completely relax from a previous contraction. The response to each stimulation builds on the previous one.

Recruitment

A process of increasing the strength of muscle contraction by increasing the number of motor units being stimulated.

Troponin

A protein on the thin (actin) filaments in muscle cells that works with tropomyosin to prevent actin and myosin from binding in the absence of calcium ions.

Tropomyosin

A protein on the thin (actin) filaments in muscle cells that works with troponin to prevent actin and myosin from binding the absence of calcium ions.

Myofibril

A rodlike bundle of contractile proteins (myofilaments) found in skeletal and cardiac muscle cells essential to muscle contractions.

Tetanus

A smooth, sustained contraction of muscle caused when stimuli are delivered in such rapid succession that there is no time for muscle relaxation.

Sarcoplasmic Reticulum

An elaborate form of smooth endoplasmic reticulum found in muscle fibers. It takes up, stores, and releases calcium ions as needed in muscle contraction.

Muscle Twitch

Contraction of a muscle in response to a single stimulus.

Origin

In reference to a muscle, the end of the muscle that is attached to the bone that remains relatively stationary during a movement.

Slow-twitch Muscle Cells

Muscle fibers that are specialized to contract slowly but with incredible endurance when stimulated. They contain an abundant supply of myoglobin and mitochondria and are richly supplied with capillaries. They depend on aerobic pathways to generate adenosine triphosphate (ATP) during muscle contraction.

Fast-twitch Muscle Cells

Muscle fibers that contract rapidly and powerful, with little endurance. They have few mitochondria and large glycogen reserves. They depend on anaerobic pathways to generate adenosine triphosphate (ATP) during muscle contraction.

Cross-bridge

Myosin heads. Club-shaped ends of a myosin molecule that bind to actin filaments and can swivel, causing actin filaments to slide past the myosin filaments, which causes the muscle contraction.

Transverse Tubules

T tubules. The tiny, cylindrical inpocketings of the muscle fiber's plasma membrane that carry nerve impulses to almost every sarcomere.

Oxygen Debt

The amount of oxygen required after exercise to oxidize the lactic acid formed during exercise.

Neuromuscular Junction

The area of contact between the terminal end of a motor neuron and the cell membrane of a skeletal muscle fiber. When an action potential reaches the terminal end of the motor neuron, acetylcholine is released, triggering events that can lead to muscle contraction.

Insertion

The end of the muscle that is attached to the bones that moves when the muscle contracts.

Sarcomere

The smallest contractile unit of a striated or cardiac muscle cell.

Myosin Filament

The thick filaments in muscle cells composed of the protein myosin and essential to muscle contraction. A myosin molecule is shaped like a golf club with two heads.

Actin Filament

The thin filaments in muscle cells composed primarily of the protein actin and essential to muscle contraction. In addition to actin, thin filaments contain two other proteins important in the regulation of muscle contraction : tropomyosin and troponin.