Locomotion And Movement

Troponin plays a crucial role in muscle contraction by regulating the binding of actin to the myosin motor. This regulation is dependent on the binding of calcium ions (Ca²⁺) to troponin.When a neural signal reaches the neuromuscular junction, it releases the neurotransmitter acetylcholine, which then generates an action potential along the sarcolemma of the muscle fiber. This action potential propagates through the muscle fiber, leading to the release of calcium ions into the sarcoplasm. The increase in calcium ion concentration enables calcium to bind to a specific subunit of troponin on the actin filaments. This binding results in the uncovering of myosin-binding sites on the actin filaments, allowing muscle contraction to proceed.

Troponin is a complex protein found at regular intervals along tropomyosin fibers in thin filaments of muscle tissue. It plays a crucial role in muscle contraction by interacting with various subunits. When a muscle is at rest, these subunits cover the active binding sites on actin, preventing interaction with myosin. During contraction, the tropomyosin-troponin complex changes conformation to reveal these binding sites, allowing myosin to bind to actin and initiate muscle contraction.

Option A: Red muscle fibres produce ATP aerobically under normal oxygen conditions.Red muscle fibers (also known as slow-twitch or Type I fibers) are rich in mitochondria, myoglobin, and have a dense capillary network. These characteristics allow them to sustain prolonged contractions by efficiently producing ATP through aerobic respiration (oxidative phosphorylation), which requires oxygen. This statement is consistent with the known physiology of red muscle fibers.Option B: Mitochondria are more in white than in red muscle fibres.Mitochondria are the primary sites of aerobic ATP production. Since red muscle fibers are specialized for aerobic respiration, they have a significantly higher number of mitochondria compared to white muscle fibers (fast-twitch or Type II fibers), which rely more on anaerobic glycolysis for quick, powerful bursts of energy. Therefore, this statement is incorrect.Option C: Lactic acid accumulates more in red than in white muscle fibres under similar conditions.Lactic acid is a byproduct of anaerobic glycolysis. White muscle fibers, being specialized for intense, short-duration activities, rely heavily on anaerobic glycolysis and thus accumulate lactic acid much more rapidly and in greater quantities than red muscle fibers, which are adapted for sustained aerobic activity and are more resistant to fatigue. Therefore, this statement is incorrect.Option D: All muscle fibres primarily produce ATP anaerobically.This is incorrect. While white muscle fibers can produce ATP anaerobically, red muscle fibers primarily produce ATP aerobically. There are also intermediate fibers (fast oxidative-glycolytic) that can utilize both pathways but red fibers are distinctly aerobic. Therefore, stating thatallmuscle fibersprimarilyproduce ATP anaerobically is false.Based on the analysis,Option Ais the only correct statement.The final answer is