Synaptic potential

Synaptic potential refers to the difference in voltage between the inside and outside of a postsynaptic neuron. In other words, it is the “incoming” signal of a neuron. Synaptic potential comes in two forms: excitatory and inhibitory. Excitatory post-synaptic potentials (EPSPs) depolarize the membrane and move it closer to the threshold for an action potential. Inhibitory postsynaptic potentials (IPSPs) hyperpolarize the membrane and move it farther away from the threshold. In order to depolarize a neuron enough to cause an action potential, there must be enough EPSPs to both counterbalance the IPSPs and also depolarize the membrane from its resting membrane potential to its threshold. As an example, consider a neuron with a resting membrane potential of -70 mV (millivolts) and a threshold of -50 mV. It will need to be raised 20 mV in order to pass the threshold and fire an action potential. The neuron will account for all the many incoming excitatory and inhibitory signals via neural integration, and if the result is an increase of 20 mV or more, an action potential will occur.