Muscle contraction

Muscle contraction is the biological process where muscle fibers shorten and generate force. The mechanism involves the interaction between **actin** (thin filaments) and **myosin** (thick filaments) proteins within muscle cells, triggered by an increase in intracellular **calcium ions** following neuronal stimulation. The key steps involve: - A nerve impulse releases **acetylcholine** at the neuromuscular junction, initiating an **action potential** in the muscle fiber membrane[1][4][5]. - The action potential spreads via **T-tubules**, causing the **sarcoplasmic reticulum** to release calcium ions[1][7]. - Calcium binds to **troponin C** in skeletal and cardiac muscle (or to **calmodulin** in smooth muscle), which exposes binding sites on actin for myosin[1][6][7]. - **Myosin heads** attach to actin and undergo a power stroke, sliding filaments past each other (the "sliding filament theory")[3][4][9]. - This cycle is powered by **ATP hydrolysis**; muscle contraction continues as long as calcium and ATP are present[8][2]. - The process terminates when calcium is actively pumped back into the sarcoplasmic reticulum, covering actin binding sites and returning the muscle to relaxation[1][5]. In summary, muscle contraction is governed by molecular targets including **acetylcholine receptor** (at the neuromuscular junction), **voltage-gated sodium channels**, **dihydropyridine receptor** (L-type calcium channel), **ryanodine receptor** (calcium release channel), **troponin**, **tropomyosin**, **actin**, and **myosin**, each of which are bona fide molecular targets for drugs and research. The process itself—"muscle contraction"—should not be considered a single molecular target.

Other names

Skeletal muscle contractionSmooth muscle contractionCardiac muscle contractionExcitation-contraction couplingSliding filament theory