GENERAL HISTOLOGY

Detailed explanation-1: -Relaxation of a Muscle Fiber. Ca++ ions are pumped back into the SR, which causes the tropomyosin to reshield the binding sites on the actin strands. A muscle may also stop contracting when it runs out of ATP and becomes fatigued. The release of calcium ions initiates muscle contractions.

Detailed explanation-2: -Eccentric muscle contraction is muscle lengthening as the muscle produces tension and the insertion moves away from the origin. The net muscle movement is in the opposite direction of the force of the muscle because the contractile force is less than the resistive force.

Detailed explanation-3: -Muscle contraction and relaxation are controlled by the intrafiber free Ca++ concentration, [Ca++]i, in the myoplasm which bathes the muscle filaments of the sarcomeres.