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Voltage gated sodium channels

The voltage gated sodium ion channels in the cell membranes of nerves and muscle are particularly sensitive to the calcium ion concentration in the plasma. Relatively small decreases in the plasma ionized calcium levels (hypocalcemia) cause these channels to leak sodium into the nerve cells or axons, making them hyper-excitable (positive bathmotropic effect), thus causing spontaneous muscle spasms (tetany) and paraesthesia (the sensation of "pins and needles") of the extremities and round the mouth. When the plasma ionized calcium rises above normal (hypercalcemia) more calcium is bound to these sodium channels having a negative bathmotropic effect on them, causing lethargy, muscle weakness, anorexia, constipation and labile emotions.