What is the effect of hypocalcemia on conduction of nerve impulse at a chemical synapse?

The reference given when answering the question about the increase in permeability of sodium ions during hypocalcemia is satisfactory but "does hypocalcemia not reduce the release of neurotransmitters at a chemical synapse" Will it not affect the speed and efficiency of conduction of impulse. Therefore how will it cause tetany?"


Increased Permeability of the Sodium Channels When There Is a Deficit of Calcium Ions.

The concentration of calcium ions in the extracellular fluid also has a profound effect on the voltage level at which the sodium channels become activated. When there is a deficit of calcium ions, the sodium channels become activated (opened) by very little increase of the membrane potential from its normal, very negative level. Therefore, the nerve fiber becomes highly excitable, sometimes discharging repetitively without provocation rather than remaining in the resting state. In fact, the calcium ion concentration needs to fall only 50 per cent below normal before spontaneous discharge occurs in some peripheral nerves, often causing muscle “tetany.”This is sometimes lethal because of tetanic contraction of the respiratory muscles. The probable way in which calcium ions affect the sodium channels is as follows:These ions appear to bind to the exterior surfaces of the sodium channel protein molecule. The positive charges of these calcium ions in turn alter the electrical state of the channel protein itself, in this way altering the voltage level required to open the sodium gate.

From: Guyton, Arthur C. Textbook of medical physiology / Arthur C. Guyton, John E. Hall.—11th ed.

Authored By Utkarsh Bansal on Tuesday 19th March 2013