Muscles

• Muscles are composed of different tissues, including muscle tissue which is composed of muscle fibres called muscle fibres.
• Each muscle fibre is packed with organelles called myofibrils.
• Myofibrils are composed mainly of two muscle filaments called actin and myosin.
• Myofibrils can be divided into functional units, each called a sarcomere.
• The functional unit of a myofibril is a sarcomere, which is contractile and made of two overlapping protein molecules: actin (Thin) and myosin (Thick).
• The sequence of events from the arrival of a nerve impulse at the neuromuscular junction to the contraction of a muscle involves the release of Calcium ion, the binding of calcium ions, the activation of troponin, the binding of calcium ions to troponin, the activation of myosin, and the contraction of a muscle.
• The structure of a myofibril consists of two types of filaments: thick and thin, each with a specific function.
• Calcium ions play a crucial role in muscle contraction by binding to troponin, a protein that regulates the interaction between actin and myosin.
• Sarcomere contraction involves the sliding of actin and myosin filaments past each other.
• Muscle fibres contain a number of proteins, including actin, myosin and collagen.
• The myosin binding site is found on actin.
• Myosin filaments are made of polypeptide chains twisted around each other with two globular heads on the end.
• ATP is hydrolysed to ADP and Pi, causing the myosin head to return to its original shape.
• Troponin and tropomyosin interact when a skeletal muscle fibre contracts.
• Other proteins in the muscle fibres include Actin, Myosin, Troponin, and Tropomyosin.
• Myosin binds to the actin using its head, causing ADP and Pi to be released.
• Many polypeptides intertwine to form the thick filaments of myosin with heads sticking out at various points.
• Calcium ions bind to the tropomyosin and cause it to detach from the Actin, exposing the binding sites.
• ATP binds to the Myosin head, causing it to release from the binding site on Actin.
• Actin is the main protein in thin filaments.
• Two strands of actin are reinforced by another protein called tropomyosin.
• ADP and Pi being released cause the head to change shape and ‘pull’ the myosin fibre over the actin fibre.
• Actin and Myosin are found in skeletal muscle and cardiac muscle, and some of the same proteins are found in both types of muscle.
• Nerve impulses and muscle contraction involve the route of nerve impulse, release of Ca 2+, and the sarcolemma (cell membrane of muscle cell), neuromuscular junction, motor neurone, calcium ions, and sarcoplasmic reticulum.