ANATOMY

Detailed explanation-1: -Stimulation of the muscle fibre, causes a wave of depolarisation to pass down the t-tubule, and the SR to release calcium ions into the sarcoplasm. Calcium is pumped back up into the SR to lower calcium ion concentration in the sarcoplasm, to relax the muscle (turn off contraction).

Detailed explanation-2: -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.

Detailed explanation-3: -When the muscle is stimulated, calcium ions are released from its store inside the sarcoplasmic reticulum, into the sarcoplasm (muscle ). Invaginations of the plasma membrane (sarcolemma) of the muscle fibres are called T (or transverse) tubules.

Detailed explanation-4: -This specialized region of the sarcolemma is known as the motor end plate, and this is the location of the ACh receptors. ACh binding causes ligand-gated Na+/K+ channels to open. These ion channels are permeable to both Na+ and K+, however, more Na+ diffuses into the cell than K+ diffuses out of the cell.