Table 1.

Classical dichotomy classification of communication modes in the central nervous system. ‘Private channel’ in WT means that the communication channel is a physically delimited pathway represented by, for example, the axon and its terminals forming synapses. ‘Widespread (diffuse)’ in VT means that the available extracellular and cerebrospinal fluid between the source and target can be used to transfer the signal.

channel	main features
wiring transmission (WT): point-to-point communication via private channels
synaptic contacts	private and highly localized transmission of transmitter signals in the synaptic cleft between neurons
gap junctions	private and highly localized transmission of signals mediated by an intercellular network of protein channels that facilitates the cell-to-cell passage of molecules, e.g. ions and neurotransmitters, mainly between astrocytes
volume transmission (VT): widespread (diffuse) communication in the extracellular space via extracellular channel plexa and in the CSF
local extracellular channel plexa mainly in the µm range (extrasynaptic VT)	broadcasted transmission linked to synaptic transmission; through extrasynaptic release and synapse spillover involving a role of local field potentials, the ions and transmitters diffuse at the local circuit level to influence nerve cells, glial cells and endothelial cells, mainly via targeting local receptors
extracellular fluid pathways mainly along paravascular and paraaxonal extracellular channels; long-distance migration, also above 1 mm	broadcasted transmission; long-distance diffusion and flow of signals in the ECF involving mainly peptides and proteins targeting distant receptors; flow is generated by temperature and pressure gradients
cerebrospinal fluid pathways; long-distance migration, also above 1 mm	broadcasted transmission; long-distance transmission of signals in the CSF, facilitated by flow generated by the arterial pulse