Question

in your own words what is the specific role of sarcolemma, sarcoplasmic reticulum, t tubules

Answer 1

Sarcolemma, sarcoplasmic reticulum and T tubules are all part of the muscle cell in a neuromuscular system.

Sarcolemma is the cell membrane of the muscle cell. It houses the acetylcholine receptors that bind to acetylcholine that are released in neuromuscular synapse by vesicle fusion in axonal membrane. Binding of ACh to AChR will also generate action potential as they have ion channels in them. This will induce the movement of calcium from terminal cisternae. Sarcolemma allows transport of ions, nutrient and wastes in and out of the cell.

Sarcoplasmic reticulum is the endoplasmic reticulum of the muscle cell. It contains the transverse tubules that contain calcium. Action potentials from the sarcolemma will stimulate the SR to release calcium ions via the ryanodine receptors. Calcium then binds troponin and releases the myosin binding sites on actin. This will stimulate cross bridging and muscle contraction.

T Tubules or Transverse tubules will conduct the electrical impulses generated by binding of ACh to its receptor in SR, down into the cells. T tubules are interconnecting rings that surround the muscle fiber. T tubules are extensions of the sarcoplasmic reticulum. Action potential conducted by T tubules activates the dihydropyridine receptors in T tubule membrane. This will activate the L-type calcium channels, which are maintained in close association with the SR. The calcium ions will activate the Ryanodine receptors in SR and cause increased release of calcium into sarcoplasm. This calcium will no stimulate muscle contraction.