Sudden decrease in serum calcium is associated with:
|A||Increased thyroxine and PTH|
|C||Increased sensitivity of muscle and nerve|
|D||Cardiac conduction abnormality|
I. The concentration of Ca in the extracellular fluid has profound effect on the voltage level at which the Na channels become activated.
II. When there is a deficit Ca the sodium channels become activated (opened) by ‘very little’ change of the membrane potential from its normal very negative resting level to a less negative level. As a result the nerve fiber becomes highly excitable, sometimes discharging repetitively without provocation instead of remaining in the resting state.
III. The probable way in which Ca++ affect the sodium channels is that calcium ions bind to the exterior surface of the sodium channel protein molecule.
IV. The positive charges on these Ca++ in turn alter the electrical state of the channel protein itself, increasing the voltage level required to open the gate