A synapse is a small gap between two neurons, or between a neuron and a muscle cell, that allows nerve impulses to pass from one cell to another.

Preload is a term that refers to the amount of tension or stress placed on a structure before it is subjected to external loads. Preload is often used in engineering and mechanics to refer to the initial tension placed on bolts, springs, and other types of fasteners.

Tonicity refers to the concentration of solutes dissolved in a solution, and how that concentration affects the movement of water across a semi-permeable membrane.