Postsynaptic potential is only one aspect of extensive communication between neurons and their synapses. Besides generating of potential changes by activation of ionic channels, neurotransmitters may activate receptors linked with the transient concentration changes of one or several intracellular second messengers, including calcium ions (Ca2+). In the neuronal cells calcium triggers and controls specific processes. Transient changes of Ca2+ concentration within the cell play an important signal role by coupling electrical and chemical impulses generated on the plasma membrane with the intracellular systems of responses. Several proteins and/or protein complexes, whose functions are directly controlled by calcium, have been identified in the neuronal cells. Their biochemical properties and physiological importance as well as cellular localization are discussed in this paper.