Can someone describe the structure of a muscle fibre?
Muscle fibres consist of parallel myofibrils which are contained in a membrane known as the sarcolemma. The cytoplasm of a muscle cell is called the sarcoplasm and within this are packed many mitochondria and the sarcoplasmic reticulum, which is arranged around the myofibrils. All of this is contained within the sarcoplasmic membrane. Skeletal muscle consists of an arrangement of thin and thick filaments that make up the myofibrils – thick filaments consist of myosin, thin filaments are made of actin. Each repeating unit of a myofibril is known as a sarcomere. In response to the arrival of an action potential, the actin and myosin filaments slide past each other, as Ca2+ ions react with troponin to activate binding sites. The bulbous head on the myosin filaments reacts with a binding site on the actin molecule, and the release of ADP causes the filaments to slide past each other in a ‘rowing’ motion – contraction. This site may also help – http://people.eku.edu/ritchisong/301notes3.htm
