Answer
Calcium is released from the terminal cisternae of the sarcoplasmic reticulum to trigger skeletal muscle contraction.
Work Step by Step
The sarcoplasmic reticulum is a system of fluid-filled sacs analogous to smooth endoplasmic reticulum(SER) in non-muscular cells. When the cell is relaxed the sarcoplasmic reticulum(SR) stores calcium(2++).The terminal cisternae are the dilated ends of SR sacs. They come into contact with the transverse invaginations of the sarcolemma (T-tubules) to for triads--formed by two terminal cisternae and one T-tubule. The T-tubule is filled with ISF and so facilitates transmission of nerve potentials. When Ca++ ions are released from the terminal cisternae ,this triggers muscle contraction.
