The X symbol looks too much like the multiplication symbol, it also makes using it as a variable more confusing.
The answer to the question mentioned above is "Synaptic Cleft".
The region composed of a presynaptic cell, its target cell and the space between them is a Synaptic Cell. This cell exists between the neurons and this is a microscopic gap.
The human body is composed of cells
Independent variables are the parts of the experiment which are changed, and dependent variables are parts of the experiment that are being measured
