mammalian muscle and contraction

• The sliding filaments are connected via cross-bridges that form and break through ATP hydrolysis.
• Muscle contraction is initiated by an action potential reaching the motor end plate at the neuromuscular junction (NMJ).
• Increased intracellular Ca2+ concentration leads to binding with troponin, exposing myosin binding sites on actin.
• Myosin heads attach to these exposed binding sites and undergo conformational changes powered by ATP hydrolysis, pulling the thin filament towards the center of the sarcomere.
• ATP hydrolysis powers the formation and breaking of cross bridges.
• Muscle contraction is initiated by the release of calcium from the sarcoplasmic reticulum, which binds to troponin and causes tropomyosin to move out of the way, exposing binding sites on actin.
• Skeletal muscles have multiple nuclei per cell, while cardiac muscle cells only have one nucleus.
• Relaxation involves the reuptake of Ca2+ into the SR, which causes tropomyosin to move over the myosin binding site.
• The striations in cardiac muscle are less distinct compared to skeletal muscle.