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Publisher Summary This chapter discusses the postsynaptic mechanisms and their effects on the relation among synaptic inputs and on firing rate. Three different locations within the motoneuron that influence this transformation are highlighted: (1) the dendrites, (2) the soma, and (3) the initial segment and axon hillock. Evoked or spontaneous activity in excitatory pre-synaptic fibers leads to transmitter release from their terminals (symbolized by the open triangle contacting the dendritic cable) and a portion of the current flowing through the ligand-gated channels reaches the soma. Spread of the current from the soma to the adjacent spike initiation zone increases the probability of spike initiation, which is reflected as a peak in the peri-stimulus time histogram (PSTH). The vast majority of synaptic contacts are found on the dendrites, as they account for over 90% of the surface area of motoneurons. Thus, factors that affect the transfer of synaptic current from a dendritic site to the soma will alter the effect of the synaptic input on motoneuron discharge behavior.