A) the concentration of calcium ions in the sarcoplasm of a resting muscle
Explanation:
Sarcoplasmic reticulum is a system of the membranous sac that is present around each myofibril and is filled with calcium ions. When muscles are in the resting stage, calcium ions are stored in the sarcoplasmic reticulum.
As the muscle action potential triggers change in voltage-gated calcium ion channels of the sarcoplasmic reticulum, the channels are opened to release the calcium ions in the sarcoplasm. Increased calcium ion levels in sarcoplasm make the muscle fibers to contract.
Removal of acetylcholine from the synaptic cleft ends the production of muscle action potential and calcium ions are moved back from the sarcoplasmic reticulum.
Hence, lower levels of calcium ions are maintained in sarcoplasm when the muscles are in the resting stage.
Uniformitarianism: assumption that the same natural laws and processes that operate in our present-day scientific observations have always operated in the universe in the past and apply everywhere in the universe.
