ANATOMY

Detailed explanation-1: -Ca++ ions bind with a unit of troponin which is responsible for masking of active sites for myosin through tropomyosin.

Detailed explanation-2: -If present, calcium ions bind to troponin, causing conformational changes in troponin that allow tropomyosin to move away from the myosin-binding sites on actin. Once the tropomyosin is removed, a cross-bridge can form between actin and myosin, triggering contraction.

Detailed explanation-3: -Troponin and tropomyosin are indispensable for the physiological regulation of striated muscle contraction. The reason why troponin is essential is straightforward to understand, because it binds calcium ions19) and changes its structure with Ca2+.

Detailed explanation-4: -Answer and Explanation: In skeletal muscle contraction, calcium apparently acts to: C) remove the blocking action of tropomyosin. Once the motor endplate potential travels from the surface down the T-tubules towards the sarcoplasmic reticulum, it signals the calcium channels to open and release calcium into the cell.

Detailed explanation-5: -Both calcium & magnesium are required for muscle contraction. Calcium binds to troponin which exposes the active sites on actin. Now myosin head can bind the active sites on actin, initiating the process of muscle contraction. The hydrolysis of ATP is used to provide energy for muscle contraction.