Muscular System - Review Flashcards

A comprehensive set of practice questions and answers covering the major topics in the Muscular System handout, including tissue types, structure, contraction mechanisms, energy use, fiber types, and muscle anatomy/naming conventions.

What percentage of body weight is made up by the muscular system?

Approximately 40% of body weight.

Name the seven primary functions of the muscular system.

Movement of the body; Maintenance of posture; Respiration; Production of body heat; Communication; Constriction of organs and vessels; Contraction of the heart.

What are the three main types of muscle tissue?

Skeletal muscle, Smooth muscle, and Cardiac muscle.

Describe skeletal muscle location and appearance.

Primarily attached to the skeletal system; striated and tubular in shape.

Describe skeletal muscle control and nuclei.

Voluntary control; multi-nucleated with nuclei at the periphery of the fiber.

How fatigable is skeletal muscle?

Easily fatigued.

What are the four key properties of skeletal muscle?

Contractility, Excitability (irritability), Extensibility, Elasticity.

What does excitability (irritability) mean for skeletal muscle?

Capacity to respond to stimuli, typically from nerves.

What does extensibility refer to in skeletal muscle?

Ability to be stretched beyond resting length without damage.

What does elasticity refer to in skeletal muscle?

Ability to recoil to original resting length after being stretched or contracted.

What are the characteristics of smooth muscle?

Found in walls of internal organs and vessels; small, spindle-shaped and not striated; involuntary; usually single central nucleus; not easily fatigued; may be autorhythmic.

What are the characteristics of cardiac muscle?

Found in the heart; long, branching, and striated; involuntary; usually single central nucleus; no fatigability; intercalated disks for unit-wide contraction.

What is the significance of intercalated disks in cardiac muscle?

Specialized cell-to-cell contacts that facilitate action potential conduction and allow cardiac cells to work as a unit.

What are the connective tissue coverings of skeletal muscle from outermost to innermost?

Epimysium (around the whole muscle), Perimysium (divides into fascicles), Endomysium (subdivides each fascicle into muscle fibers).

What is a muscle fiber?

A single cylindrical muscle cell, up to 30 cm long.

What is the sarcolemma?

The cell membrane of a muscle fiber.

What are T-tubules?

Tubelike invaginations that extend inward and connect the sarcolemma to the sarcoplasmic reticulum.

What is the sarcoplasmic reticulum?

A highly organized smooth endoplasmic reticulum that stores Ca2+ for muscle contraction.

What is the sarcoplasm?

The cytoplasm within a muscle fiber.

What are myofibrils?

Numerous threadlike structures containing actin and myosin filaments.

What are sarcomeres?

Highly ordered repeating units of actin and myosin; basic contractile units of skeletal muscle.

What are the two main types of myofilaments and their basic roles?

Actin (thin filaments) and Myosin (thick filaments).

What proteins regulate actin-myosin interaction in a relaxed muscle?

Troponin (binds Ca2+) and Tropomyosin (blocks myosin binding sites on actin when unstimulated).

Describe the structure of myosin filaments.

Thick filaments resembling bundles of minute golf clubs with myosin heads that bind actin, bend/straighten during contraction, and hydrolyze ATP.

What is the Sliding Filament Model of muscle contraction?

Actin and myosin filaments slide past each other, shortening sarcomeres and the whole muscle in response to a motor neuron action potential.

What initiates the cross-bridge cycle at the neuromuscular junction?

Acetylcholine (ACh) is released, binds to receptors on the sarcolemma, opening Na+ channels and triggering an action potential that leads to Ca2+ release from the sarcoplasmic reticulum.

What role does Ca2+ play in contraction?

Ca2+ binds to troponin, causing tropomyosin to move and expose myosin attachment sites on actin, enabling cross-bridge formation.

What is the energy source for the power stroke in contraction?

ATP fuels the myosin head cycle, allowing attachment, pulling (power stroke), and detachment of cross-bridges.

What is rigor mortis?

After death, ATP is unavailable, preventing cross-bridge detachment and causing muscle rigidity.

What happens during muscle relaxation?

Ca2+ is pumped back into the sarcoplasmic reticulum, tropomyosin covers actin binding sites, and cross-bridge formation stops.

What is a muscle twitch and its three phases?

A single contraction of a muscle fiber with lag (latent) phase, contraction phase, and relaxation phase.

What is summation in muscle contraction?

Increased force from rapid stimulation, leading to incomplete or complete tetanus (sustained contraction with little to no relaxation).

What is motor unit recruitment?

Increasing the number of contracting muscle fibers by stimulating more motor units to produce greater force.

Describe aerobic respiration in muscle energy use.

Requires O2; more ATP per glucose; slower; predominant in low-intensity, long-duration activity and slow-twitch fibers.

Describe anaerobic respiration in muscle energy use.

Does not require O2; rapid ATP production but less efficient; produces lactate; dominant in high-intensity, short-duration activity and fast-twitch fibers.

What is the role of creatine phosphate in energy supply?

Provides a rapid reserve to regenerate ATP at the onset of exercise.

What happens to ADP during heavy exercise?

Two ADP molecules can be converted to one ATP and one AMP.

How is fatigue defined?

A temporary state of reduced work capacity, acting as a protective mechanism to prevent damage.

List major fatigue mechanisms.

Acidosis and ATP depletion; oxidative stress; local inflammatory reactions; physiological contracture; psychological fatigue.

What are slow-twitch (Type I) fibers like?

High aerobic capacity; high fatigue resistance; slow contraction; smaller diameter; high myoglobin; many mitochondria; abundant in postural muscles.

What are Type IIa fast-twitch fibers like?

Intermediate aerobic/anaerobic capacity; intermediate fatigue resistance; fast contraction.

What are Type IIb fast-twitch fibers like?

Largest diameter; low myoglobin (hence white meat); highest anaerobic capacity; fastest contraction.

What factors influence fiber type ratios and hypertrophy?

Hereditary factors; training can influence the ratio of fiber types and cause muscle hypertrophy.

What is isometric contraction?

Muscle length does not change, but tension increases.

What is isotonic contraction?

Tension remains constant while muscle length changes.

What is concentric contraction?

Muscle tension increases as it shortens.

What is eccentric contraction?

Muscle tension is maintained while the muscle lengthens; can cause injury.

What is muscle tone?

Constant tension produced by muscles over long periods to maintain posture; small percentages of motor units contract tetanically out of phase.

What are the basic attachment sites of a skeletal muscle?

Origin (stationary end) and Insertion (part that moves); Belly is the thickest part between origin and insertion.

What are aponeuroses and retinaculum?

Aponeuroses are broad sheet-like tendons; retinaculum is a band of connective tissue that holds tendons in place around joints.

What are agonists, antagonists, synergists, and fixators?

Agonist: prime mover; Antagonist: opposes movement; Synergists: assist; Fixators: immobilize a bone to stabilize the base of movement.

How are skeletal muscles named (nomenclature concepts)?

Based on location, shape, size, direction of fibers, number of origins, origin-insertion, and function.

What are fascicle arrangements and their basic shapes?

Circular; Convergent; Fusiform; Parallel; Pennate (Unipennate, Bipennate, Multipennate).