A presynaptic neuron may release a neurotransmitter onto a post synaptic membrane opening Na or Ca ion gates decreasing the membrane potential thereby depolarizing the membrane.

The post synaptic potential generated is referred to as an EPSP, an excitatory post synaptic potential.

When the membrane potential reaches -55 mV an action potential is generated, continuing the communication train.

A presynaptic neuron may release a neurotransmitter onto a post synaptic membrane opening K or Cl ions, increasing the membrane potential, thereby hyperpolarizing the membrane.

The post synaptic potential generated is referred to as an IPSP, an inhibitory post synaptic potential, making it more difficult to reach action potential.

These post synaptIc potentials can summate and be timed to modulate post synaptic activity.