Final answer:
High calcium levels in the cytosol are lowered through calcium efflux, calcium sequestration, and calcium binding to neurotransmitters.
Step-by-step explanation:
When a nerve signal stops, high calcium levels in the cytosol are lowered by calcium efflux, calcium sequestration, and calcium binding to neurotransmitters. Calcium efflux refers to the active transport of calcium ions out of the cytosol, helping to restore the low calcium concentration. Calcium sequestration involves the removal of calcium ions from the cytosol into intracellular compartments, such as the endoplasmic reticulum. Lastly, calcium binding to neurotransmitters helps to regulate calcium levels by reducing its free concentration in the cytosol.