Would it make a difference if calcium bromide solution, cabr2, were used rather than sodium bromide solution?

No it would not because solubility would not be affected since bromine is the only element in the reaction that is involved in the reaction.

The answer is c - the principal of original lateral continuity. 

Each calcium ion has a charge of +2, which can also be written as ca2+. if those ions move out of the neuron and no other ions are moving, the neuron would lose the positive charge associated with those ions and become more negatively charged.