How Long Does it Take to Earn a PhD? A PhD usually requires at least five to six years and many people take seven to nine years. Masters vs PhD: Which One Costs More? The old adage time is money was never so true as with graduate school; as a PhD takes longer to complete, it also requires more money.
Once the active site is exposed, the myosin head (which has a strong affinity for the active site) binds and the cross bridge cycle begins. Sources of Calcium in smooth muscle cells Unlike skeletal muscle, smooth muscle is dependent on two sources of calcium in order to initiate contraction.
How do calcium ions initiate contraction in skeletal muscle fibers? A. Calcium ions provide the energy necessary for the myosin head power stroke. B. Calcium ions bind to tropomyosin, exposing the active sites on actin. C. Calcium ions bind to troponin, changing troponinâs shape.