Skeletal Muscle

Skeletal muscles are a large grouping of cells with the intended purpose of contraction and relaxation. These two motions are what allows animals to move. Skeletal muscles are composed of myosin and actin filaments compacted into a small area known as a sarcomere. This sarcomere is the contractile unit of the cell. A strand of sarcomeres is known as a muscle fiber, a group of muscle fibers is called a fascicle, and fascicles make up a skeletal muscle. Skeletal muscles are actively controlled by the brain. When an organism wants to move their brain fires signals known as action potentials down a system of nerves to reach the muscle. The nerves connect to the muscle and when the action potential reaches this point the action potential is potentiated along the sarcolemma of the muscle. The sarcolemma is the muscle cells storage and transport system. Eventually while moving across the muscle, the action potentials travel down t-tubules, which activate voltage-gated ion channels. These channels open calcium stores to be released into the muscle.The calcium reaches the sarcomere and binds to troponin, a portion inhibiting myosin from binding to actin. Binding calcium to troponin causes a conformational change and exposes the active sites on actin. Myosin heads on the myosin are where contraction actually occurs. In there off state they are bound to an atp, which can be broken and release energy stored in the bonds activating the myosin head. In this state the myosin head can bind to the exposed sites on actin and pull/contract. At the same time the ADP and P molecules still attached release. Returning the myosin head to ‘rest’ requires an ATP to bind changing its conformation and decreasing its affinity for the binding pocket.