A synaptic potential is an alteration in the membrane potential

Membrane potential

Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...

 of a cell resulting from activation of a synaptic input

Chemical synapse

Chemical synapses are specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to form circuits within the central nervous system. They are crucial to the biological computations that underlie...

. 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 neuron

Neuron

A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

s can alter this voltage difference. If the intracellular voltage rises, the signal is called an excitatory postsynaptic potential

Excitatory postsynaptic potential

In neuroscience, an excitatory postsynaptic potential is a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand-sensitive channels...

 (EPSP); if it falls the signal is called an inhibitory postsynaptic potential

Inhibitory postsynaptic potential

An inhibitory postsynaptic potential is a synaptic potential that decreases the chance that a future action potential will occur in a postsynaptic neuron or α-motoneuron...

 (IPSP). If the cell is electrically excitable, a sufficiently large EPSP may cause it to generate an action potential

Action potential

In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...

.