Skeletal Muscle Contraction and Excitation-Contraction Coupling

Vocabulary flashcards covering the cellular structures, proteins, signaling pathways, and biomechanical stages of skeletal muscle excitation-contraction coupling and contraction.

Excitation-contraction coupling

The physiological process through which electrical excitation of the muscle fiber membrane leads to mechanical contraction and force generation.

Transverse tubules (t-tubules)

Folds in the muscle fiber cell membrane that allow action potentials traveling on the surface to propagate deep within the cell.

Myofibrils

Cylindrical structures buried deep within the skeletal muscle cell that contain sarcomeres.

Sarcomeres

Contractile structures within myofibrils composed of actin and myosin that shorten to produce muscle contraction and force.

Sarcoplasmic reticulum (SR)

A spider-web-like organelle surrounding myofibrils that functions as a high-concentration calcium storage center.

$Ca^{2+}$ ATPase

A protein transporter that uses energy from ATP to pump calcium ions from low concentration outside the SR to higher concentration inside the SR.

DHP

A voltage-gated receptor on the t-tubule membrane physically linked to RyR that changes shape in response to an action potential to pull RyR open.

RyR

A calcium channel on the sarcoplasmic reticulum membrane that serves as a gate, opening when pulled by DHP to release calcium into the sarcoplasm.

Sarcoplasm

The cytoplasm of the muscle cell into which calcium ions flood when RyR channels open.

Thick filament

A contractile myofilament within the sarcomere composed primarily of the protein myosin.

Thin filament

A contractile myofilament within the sarcomere composed primarily of actin, along with regulatory proteins tropomyosin and troponin.

Tropomyosin

A regulatory protein along the thin filament that blocks myosin from binding to the binding sites on actin.

Troponin

A regulatory protein on the thin filament that binds calcium ions, inducing a shape change in tropomyosin to expose actin's binding sites.

Power stroke

The mechanical step in the cross-bridge cycle where myosin releases inorganic phosphate and pulls actin toward the center of the sarcomere, generating force.

Rigor state

The state during the cross-bridge cycle occurring after ADP is released, where myosin remains tightly bound and stuck to actin.

Cross-bridge cycle

The multi-step cyclical mechanism wherein myosin hydrolyzes ATP, binds actin, executes a power stroke, and binds a new ATP molecule to detach.

Sliding filament theory

The concept explaining muscle contraction where thick and thin filaments slide past one another to shorten the sarcomere without shortening the individual filaments themselves.

Rigor mortis

The post-mortem phenomenon in which muscles contract and remain stiff for hours or days because breakdown of the SR membrane releases calcium while the lack of ATP prevents myosin from unbinding actin.