the excitation meachanical coupling occurs through the coupling of the DHP and RYR proteins where the signal action potential becomes the release of calcium from the SR

3 Na in : 1 Ca out - Na Ca exchanger

• a) Explain the role of the transverse tubules, and the terminal cisternae in skeletal muscle contraction

there is a ‘’triad’’ of SR and T tubules, the action potential signal travels through the transverse tubules and it diffuses into the terminal cisternae of the SR which then causes the release of Ca

• b) Explain the role of 'junctional foot proteins' and the role of the ryanodine and dihydropyridine receptor binding proteins

• c) Detail the changes in the cytoplasmic calcium concentration during activation and relaxation

during activation cytoplasmic calcium conc is increased but never greater than within the SR, during relaxation it decreases into nanomolar concentrations as Calcium is pumped out of the cell or into the SR in the cell.

• d) Explain the importance of Ca-ATPase and calsequestrin

calsequestrian binds to approx 42 calcium ions per molecule and holds free calcium and releases it into the SR once an action potential has occured to ensure that the gradient is restored

SERCA (Ca-ATPase) - is an active transport pump which worls off of ATP to transfer Ca up its concentration gradient into the Sarcoplasmic reticulum (SR)

therefore both of these proteins are essential in maintaining the correct gradients in muscle cells and ensuring contraction does not unwantedly occur.