<prompt> Presynaptic facilitation is caused byProlonged opening of calcium channelsProlonged opening of chloride channelsProlonged opening of sodium channelsProlonged closure of potassium channels  <response>: Presynaptic facilitation: when a third neuron facilitates the presynaptic neuron at it ternimal end is called presynaptic facilitation It causes increased neurotransmitters by opening ca channals Ref:Guyton and Hall textbook of medical physiology 12th edition,page number:675,676,677 