How do calcium ions participate in muscle contraction? Why do both muscle contraction and muscle relaxation spend energy?
In the muscle cells calcium ions are kept within the sarcoplasmic reticulum. When a motor neuron emits stimulus for the muscle contraction neurotransmitters known as acetylcholine are released in the neuromuscular junction and the sarcolemma is excited. The excitation is conduced to the sarcoplasmic reticulum that then releases calcium ions into the sarcomeres.