Skeletal Muscle Flashcards

Muscle fibers

Long, cylindrical cells that make up skeletal muscle tissue; multinucleated and striated.

Endomysium

Thin connective tissue surrounding each muscle fiber.

Perimysium

Connective tissue that wraps around bundles of muscle fibers (fascicles).

Fasciculus (fascicle)

A bundle of muscle fibers surrounded by perimysium.

Epimysium

Dense connective tissue surrounding the entire muscle.

Tendons

Tough, fibrous connective tissue attaching muscle to bone.

Periosteum

Dense membrane covering bone where tendons attach.

Origin (of a muscle)

The fixed attachment point.

Insertion (of a muscle)

The movable attachment point.

Muscle contraction effect on origin and insertion

It pulls the insertion toward the origin.

Force of muscle contraction affects

Cross-sectional area and number of motor units activated.

Striated appearance (muscle)

Regular arrangement of actin and myosin filaments.

Sarcolemma

The plasma membrane of a muscle fiber.

Sarcoplasm

Cytoplasm of a muscle fiber; contains organelles and glycogen.

Sarcoplasmic Reticulum (SR)

Specialized ER that stores and releases calcium for muscle contraction.

Satellite cells

Muscle stem cells involved in growth and repair.

Chemical composition of muscle

75% water, 20% proteins, 5% salts and other substances.

Contractile proteins (main)

Actin and myosin.

Regulatory proteins (main)

Troponin and tropomyosin.

Structural proteins (main)

Titin and nebulin.

Rich capillary network importance in muscles

It delivers oxygen and removes waste.

Aerobic exercise effect on muscles

Increases capillary density, mitochondrial content, and oxidative enzymes.

"Milking action"

Muscle contractions help pump blood through veins.

Straining exercises effect on blood flow

They may temporarily compress blood vessels and limit flow.

Endurance training effect on capillarization

It improves capillary density, supporting oxygen delivery.

Myofibrils

Thread-like structures in muscle fibers containing sarcomeres.

Myofilaments

Protein filaments within myofibrils.

Thick and think filaments

Thick: myosin; Thin: actin.

Sarcomere

The structural and functional unit of a myofibril (z-line to z-line).

PCSA

Physiological cross-sectional area; correlates with muscle force.

Fiber-to-muscle length ratio affect on function

It affects speed and range of motion.

Fascicle arrangements

Parallel, fusiform, pennate (uni-, bi-, multi-), convergent, circular.

Actin and myosin function

Actin: thin filaments with binding sites; Myosin: thick filaments with heads (cross-bridges).

Cross-bridges function

Myosin heads bind to actin to generate force.

Troponin and tropomyosin role

They regulate access to actin binding sites.

T-tubules

Invaginations of the sarcolemma that transmit action potentials into the muscle fiber.

Intracellular tubule system

Includes the SR and T-tubules; coordinates calcium release.

Sliding filament theory

Actin and myosin slide past each other, shortening sarcomeres.

Cross-bridges mechanical work

Myosin heads pull actin filaments using ATP.

ATP role in contraction

ATP binds to myosin, allowing detachment and resetting.

Excitation-contraction coupling steps

1. Action potential travels down T-tubules

2. 2. SR releases Ca²

3. 3. Ca² binds to troponin → exposes actin sites

Power stroke

Myosin head pivots, pulling the actin filament.

Muscle relaxation occurs

Ca² is reabsorbed by SR, and binding sites are blocked by troponin/tropomyosin.

Muscle action sequence

Nerve impulse → muscle shortening → relaxation.

Fast-twitch fibers

Fibers with quick, powerful contractions; fatigue faster.

Type II X fiber

High power, low endurance.

Type II A fiber

Intermediate, more fatigue-resistant than Type II X.

Slow-twitch (Type I) fibers

Slower contractions, high endurance, oxidative metabolism.

Sprinters muscle fibers

Fast-twitch fibers.

Endurance athletes muscle fibers

Slow-twitch fibers.

Muscle fiber types change with training

Some conversion between Type II X and Type II A is possible; Type I ↔ Type II is unlikely.

Metabolic adaptations to training

Increased mitochondrial density, enzyme activity, and glycogen storage.

Hypertrophy

Increase in muscle fiber size.

Hyperplasia

Increase in fiber number (controversial in humans).

Sarcopenia

Age-related loss of muscle mass, strength, and function.

Myofascial pain

Chronic pain from trigger points in fascia and muscle, often due to overuse or imbalances.

What does "excess muscle” refer to?

Hypertrophy beyond functional need can restrict movement or cause imbalance