Muscular System Flashcards

Skeletal (voluntary, striated), Cardiac (involuntary, striated, intercalated discs), Smooth (involuntary, non-striated, found in organs and blood vessels).

Muscle contraction occurs when thin filaments (actin) slide past thick filaments (myosin), shortening the sarcomere. Myosin heads bind to actin, pull, release, and repeat.

The basic contractile unit of skeletal muscle, running from one Z-line to the next. Contains overlapping actin (thin) and myosin (thick) filaments.

Calcium is released from the sarcoplasmic reticulum, binds to troponin on actin filaments, which moves tropomyosin to expose binding sites for myosin. No calcium means no contraction.

The synapse between a motor neuron and a muscle fiber. The neuron releases acetylcholine (ACh), which binds to receptors on the muscle cell membrane (sarcolemma) and triggers contraction.

ATP powers the myosin head to detach from actin and reset for the next power stroke. Without ATP, myosin stays bound to actin (rigor). ATP also powers the calcium pump to end contraction.

Isometric: muscle generates force but does not change length (pushing against a wall). Isotonic: muscle changes length while maintaining tension (lifting a weight).

Concentric: muscle shortens (bicep curl on the way up). Eccentric: muscle lengthens under tension (bicep curl on the way down, controlling the weight).

Origin: the attachment point that remains stationary during contraction (usually proximal). Insertion: the attachment that moves (usually distal).

Agonist: the muscle primarily responsible for a movement. Antagonist: the muscle that opposes the agonist. Example: biceps brachii (agonist) and triceps brachii (antagonist) during elbow flexion.

Front of the thigh (4 muscles: rectus femoris, vastus lateralis, vastus medialis, vastus intermedius). Extends the knee. Primary muscle for standing up, climbing stairs, and kicking.

Back of the thigh (3 muscles: biceps femoris, semitendinosus, semimembranosus). Flexes the knee and extends the hip.

A dome-shaped skeletal muscle separating the thoracic and abdominal cavities. Primary muscle of respiration. When it contracts, it flattens and increases thoracic volume, drawing air into the lungs.

A triangular muscle covering the shoulder joint. Abducts the arm (raises it to the side). Has anterior, lateral, and posterior heads for different movements.

Slow-twitch (Type I): fatigue-resistant, use aerobic metabolism, endurance activities. Fast-twitch (Type II): powerful but fatigue quickly, use anaerobic metabolism, sprinting and heavy lifting.

The constant, low-level contraction of muscles even at rest. Maintains posture and keeps muscles ready for action. Controlled by involuntary nerve impulses.

A specialized endoplasmic reticulum in muscle cells that stores and releases calcium ions to regulate contraction.

A single motor neuron plus all the muscle fibers it innervates. Small motor units (few fibers) allow fine control (eyes, fingers). Large motor units (many fibers) produce powerful movements (legs, back).

Primarily ATP depletion and accumulation of metabolic byproducts (hydrogen ions, inorganic phosphate). Lactic acid buildup is a marker but not the primary cause.

Stiffening of muscles after death. Without ATP, myosin heads cannot detach from actin, locking the muscles in a contracted state. Resolves as muscle proteins begin to decompose.