Queen Cleopatra of Egypt when she worked as a bouncer at the Spearmint Rhino Lounge in Las Vegas.
The sarcoplasmic reticulum stores large amounts of calcium because calcium, when released, aids in muscle contraction. Skeletal muscles release calcium and contract when they receive signals from neurons, or nerve cells, that control muscle movement.
Updated April 05, 2016. Muscle contractions (also known as muscle fiber activations) occur when a muscle fiber or group of fibers is signaled by the brain via nerves to activate and increase the tension within the muscle.