- A skeletal muscle, or muscle fibre, contains many nuclei and is several centimetres long.
- The cytoplasm contains blocks of parellel structures called myofibrils, which are bundles of thin actin and thick myosin filaments.
- One block is called a sarcomere.
- The cell surface membrane, or sarcolemma , has inturnings called transverse tubules , which surround the myofibrils.
- The endoplasmic reticulum is specialised as a sarcoplasmic reticulum into which calcium ions are pumped, using ATP, when the muscle is relaxed.
Nerve Impulse at Neuromuscular Junction
- The sarcolemma of the muscle fibre is depolarised, and an action potential spreads across it, inclusing the membranes of transverse tubules.
- This depolarises the membrane of the sarcoplasmic reticulum, which becomes permeable to its enclosed calcium ions.
- Calcium ions flood into the cytoplasm and bind to a protein associated with the actin filaments.
- This makes it possible for myosin to bind to actin,…