When calcium levels increase, what happens to the threshold?

When calcium levels increase, the threshold for action potentials in excitable tissues, such as nerve and muscle cells, increases. Higher levels of extracellular calcium stabilize the cell membrane by reducing its permeability to sodium. This stabilization raises the threshold needed to initiate an action potential because the influx of sodium ions is necessary for depolarization to occur.

In this context, an increased threshold means that a stronger stimulus is required to trigger an action potential compared to when calcium levels are normal or lower. This physiological mechanism is critical because it helps regulate excitability in tissues and plays a role in preventing excessive neuronal firing and muscle contractions.

Thus, understanding the relationship between calcium levels and action potential thresholds is essential for various clinical situations, especially in conditions involving electrolyte imbalances.