A synaptic potential (also known as a postsynaptic potential) is an alteration in the membrane potential of a cell resulting from activation of a synaptic input. All animal cells maintain a voltage difference between the intracellular and extracellular regions, holding the intracellular region at a negative voltage that in a baseline state is usually in the range -30 to -70 millivolts. Synaptic inputs from neurons can alter this voltage difference. If the intracellular voltage rises, the signal is called an excitatory postsynaptic potential (EPSP); if it falls the signal is called an inhibitory postsynaptic potential (IPSP). If the cell is electrically excitable, a sufficiently large EPSP may cause it to generate an action potential.