Despite the great diversity of neurons in the nervous system, there are a number of typical properties shared by the vast majority of neurons. First, neurons have common morphological features. They are characterized by a cellular polarization and typically extend multiple arborizing dendrites and one single axon from the cell body (soma). Because of these unique structural properties, neurons also express specific cytoskeletal proteins such as neurofilaments, microtubules and microtubule-associated proteins. In addition, neurons have unique membrane characteristics with the presence of numerous constitutively open, voltage-gated, or transmitter-dependent, ion channels and intracellular second messenger-regulated metabotropic receptors. Together, these proteins confer the passive and active membrane properties of neurons. Finally, neurons are characterized by their ability to form synapses, which are specialized cell-cell contacts between an axon terminal and the soma or a dendrite where neurotransmission takes place. Please note, that not all neurons receive synaptic input from other neurons (e.g. primary sensory neurons), every neuron has output function and in most cases in form of synapses with other neurons (neuromodulatory neurons such as dopamine neurons are believed to not form classical synapses).
