What is the sequence of events that converts action potentials in a muscle fiber to a contraction

Explain why in any given geographical region, women tend to have lighter skins( by 3-4% on average) than men?

The gene that causes sickle-cell disease is present in a higher percentage of residents of sub-saharan africa than among those of african descent living in the united states. even though this gene causes sickle-cell disease, it also provides some protection from malaria, a serious disease that is widespread in sub-saharan africa but absent in the united states. discuss an evolutionary process that could account for the different percentages of the sickle-cell gene among residents of the two regions.

What are the most explosive events that occur on the sun? umbras solar flares solar winds prominences