What role do calcium ions play in contraction of the sarcomere? (4 marks)
- When an action potential arrives at the motor end plate it causes depolarisation to occur in the sarcolemma of the effector muscle cells.2) Depolarisation spreads via T-tubules to the sarcoplasmic reticulum leading to release of stored calcium via voltage gated calcium ion channels into the cytoplasm of the skeletal muscle cell (sarcoplasm).3) Cytosolic calcium ions can then bind to troponin inducing a conformational change that removes tropomyosin from the actin-myosin binding site of the actin filament. 4) The myosin head is then able to bind to the actin filament allowing the process of cross-bridge cycling to begin resulting in muscle contraction.Extra (beyond A level)- Calcium is pumped back into the sarcoplasmic reticulum via SERCA pumps in its membrane. As the calcium ion concentration in the cytosol returns to normal; relaxation of the muscle can occur.
