muscle tissue- quantitative BME

Contractility

Ability of muscle tissue to generate tension and contract in response to stimulation.

Epimysium

Outermost connective tissue layer surrounding an entire skeletal muscle.

Perimysium

Connective tissue layer surrounding and organizing muscle fibers into fascicles.

Endomysium

Thin connective tissue layer surrounding each individual muscle fiber.

Fascicle

Bundle of skeletal muscle fibers surrounded by perimysium.

Tendon

Dense connective tissue that connects muscle to bone and transfers muscle force to the skeleton.

Aponeurosis

Broad, flat, tendon-like sheet of connective tissue.

Sarcolemma

Plasma membrane of a muscle fiber.

Sarcoplasm

Cytoplasm of a muscle fiber.

Sarcoplasmic reticulum

Specialized smooth ER in muscle that stores and releases calcium ions.

Sarcomere

Basic contractile unit of striated muscle located between two Z-discs.

Tropomyosin

Protein that covers myosin-binding sites on actin when skeletal muscle is relaxed.

Troponin

Protein complex that binds calcium and causes tropomyosin to move away from actin's myosin-binding sites.

Myofibril

Long contractile structure within a muscle fiber composed of repeating sarcomeres.

Actin

Protein that forms the thin filaments of a sarcomere.

Myosin

Protein that forms the thick filaments and pulls on actin during contraction.

Neuromuscular junction

Junction where a motor neuron communicates with a skeletal muscle fiber.

Motor end plate

Specialized region of the muscle sarcolemma containing acetylcholine receptors at the neuromuscular junction.

Excitation-contraction coupling

Process linking electrical excitation of a muscle fiber to its contraction.

Acetylcholine (ACh)

Neurotransmitter released by motor neurons at the neuromuscular junction to activate skeletal muscle.

Cross-bridge

Connection formed when a myosin head binds to actin.

Sliding filament model

Model in which thin actin filaments slide past thick myosin filaments to shorten the sarcomere.

Creatine phosphate

High-energy molecule that rapidly regenerates ATP by donating a phosphate to ADP.

Oxygen debt

Additional oxygen required after exercise to restore the body and muscles toward resting conditions.

Muscular dystrophy

Group of disorders characterized by progressive muscle weakness and degeneration.

Dystrophin

Protein that helps stabilize muscle fibers by linking the internal cytoskeleton with structures associated with the cell membrane.

Duchenne muscular dystrophy

X-linked muscular dystrophy caused by loss of functional dystrophin and primarily affecting males.

Isotonic contraction

Contraction in which muscle length changes while a load is moved.

Concentric contraction

Contraction in which a muscle shortens while producing force.

Eccentric contraction

Contraction in which a muscle lengthens while producing force.

Isometric contraction

Contraction that produces tension without changing muscle length or joint angle.

Motor unit

One motor neuron and all of the muscle fibers it innervates.

Small motor unit

Motor unit in which one motor neuron innervates few muscle fibers, allowing fine motor control.

Large motor unit

Motor unit in which one motor neuron innervates many muscle fibers, allowing gross or powerful movement.

Size principle

Motor units are recruited from smaller units to larger units as more force is required.

Length-tension relationship

Relationship in which muscle force depends on sarcomere length and the amount of effective actin-myosin overlap.

Twitch

Single contraction-relaxation response of a muscle to one stimulus.

Treppe

Progressive increase in contraction strength during repeated stimulation when the muscle completely relaxes between stimuli.

Muscle tone

Continuous low-level muscle contraction that helps maintain posture and muscle readiness.

Hypotonia

Abnormally low muscle tone.

Hypertonia

Abnormally high muscle tone.

Slow oxidative fiber

Slow-contracting, aerobic, fatigue-resistant skeletal muscle fiber.

Fast oxidative fiber

Fast-contracting fiber that primarily uses oxidative metabolism and has moderate fatigue resistance.

Fast glycolytic fiber

Fast and powerful fiber that relies heavily on glycolysis and fatigues quickly.

Myosin ATPase

Enzyme activity of myosin that hydrolyzes ATP and influences contraction speed.

Oxidative metabolism

Aerobic ATP production that uses oxygen and supports prolonged muscle activity.

Glycolytic metabolism

ATP production through glycolysis that supports rapid activity but is less fatigue resistant.

Hypertrophy

Increase in muscle fiber size.

Atrophy

Decrease in muscle fiber size, often caused by disuse, aging, or loss of neural stimulation.

Intercalated disc

Specialized connection between neighboring cardiac muscle cells.

Gap junction

Channel between neighboring cells that allows ions and electrical signals to pass directly from cell to cell.

Pacemaker cell

Cardiac cell that spontaneously generates electrical activity and helps establish heart rhythm.

Functional syncytium

Group of electrically connected muscle cells that function together as a coordinated unit.

Dense body

Smooth-muscle structure analogous to a Z-disc that anchors contractile filaments.

Caveolae

Small indentations of the smooth-muscle cell membrane involved in calcium signaling.

Calmodulin

Calcium-binding regulatory protein involved in activating smooth-muscle contraction.

Myosin light-chain kinase (MLCK)

Enzyme activated by the calcium-calmodulin complex that phosphorylates myosin and promotes smooth-muscle contraction.

Latch-bridge

Smooth-muscle mechanism that allows tension to be maintained for long periods while using relatively little ATP.

Hyperplasia

Increase in the number of cells through cell division.

Mesoderm

Embryonic germ layer from which muscle tissue primarily develops.

Myoblast

Immature muscle precursor cell that can develop into muscle tissue.

Myotube

Multinucleated developing muscle structure formed by fusion of multiple myoblasts.

Satellite cell

Adult skeletal-muscle stem/progenitor cell involved in muscle growth and repair.