neurotransmitter was released when in the experiment having no Ca++ in the extracellular fluid because is Ca++ dependent.

Mg++ the effect of extracellular calcium by blocking and neurotransmitter release.

What change in membrane potential triggers the action potential? 

Under resting conditions potassium ions move ___ the neuron through ____ channels.

Stronger stimuli are able to increase the frequency of action potentials by intruding on the:

Put the events occurring at a ligand gated channel in the correct order.

What happened to the amount of neurotransmitter release when you switched from the extracellular fluid with no Ca++ to the extracellular fluid with low Ca?

The absolute refractory period is the result of voltage gated channels being , which means that they cannot be opened regardless of stimulus strength.  (refer to the Vander textbook if needed.)

Activity 5:  How does the absolute refractory period ensure directionality of action potential propagation? Include the role of Na+ voltage gated channels.

The action potential changes the membrane potential from mV (resting) to mV and back again to the resting membrane potential. This is the result of a change in membrane permeability first to ions then to ions due to the opening of gated channels.