The output region is the site of
a. protein synthesis
b. ligand gated channels
c. voltage gated na+ channels
d. neurotransmitter release

The correct answer is option C (voltage gated Na+ channels).

Explanation:

Output region or axon terminal is the structure of neuron which transmits the signals to other nerve cells.

The signal is transferred via action potential generated by the dendrite cell which moves along the axon and reaches the synaptic junction.  

At the synaptic junction, voltage-gated channel (Na+) channels located in the membrane of the axon terminal cell opens due to the changes in the electric membrane potential which play important role in returning the depolarized cell to a resting state.

Thus, option C (voltage-gated Na+ channels) is the correct answer.