Which of the following best represents the principle of the all-or-none law?
◦ The fact that a cell must enter a refractory period after firing to restore its own resources.
◦ The fact that a neurotransmitter is either excitatory or inhibitory, but never both.
◦ The fact that once a cell reaches its threshold, it must fire and cannot be stopped.
◦ The idea that cells in a network must all be excited at the same time for a behavior to occur.