Q.Write a short note on: Role of calcium ions in the contraction and relaxation of muscles.

Step 1: Role in contraction. When a nerve impulse reaches a muscle fibre, it travels down the T tubules and causes the sarcoplasmic reticulum to release a large number of calcium ions into the sarcoplasm. These calcium ions bind to troponin, whose strong affinity for calcium causes a change in its shape; this shift pulls tropomyosin away from actin's active sites, uncovering them so that the ATP-charged myosin head can attach and begin the cross-bridge cycle that produces contraction. …

Trace calcium's presence/absence in the sarcoplasm through both the contr …

• Describing calcium's role only in contraction and omitting its (equally active, ATP-requiring) removal during relaxation. …