Muscle contraction is a complex physiological process in which muscle fibers generate tension and shorten in length. This process is essential for various bodily functions, including movement, maintaining posture, and facilitating organ functions like the heart's pumping action. Here are the key points about muscle contraction: Muscle Fibers: Muscles are composed of individual muscle fibers, each containing many myofibrils. Sliding Filament Theory: Muscle contraction is primarily explained by the sliding filament theory. According to this theory: Myosin (thick) and actin (thin) filaments within muscle fibers slide past each other. Cross-bridges formed by myosin heads attach to actin filaments, pulling them closer together. This shortens the sarcomere, the basic contractile unit of a muscle, leading to overall muscle contraction. Neuromuscular Junction: Muscle contraction is initiated by nerve impulses. When a motor neuron signals a muscle to contract, it releases the neurotransmitter acetylcholine at the neuromuscular junction. This triggers an action potential in the muscle fiber. Calcium Ion Release: The action potential travels along the muscle fiber and into the sarcoplasmic reticulum, a specialized organelle that stores calcium ions (Ca2+).