The Electrically Dancing Neuron

Dendrites – with their most aesthetic tree-like structure- are the major receptive region of nerve cells. Thousands of synaptic inputs from other nerve cells bombard the dendritic tree and consequently, the dendritic membrane undergoes numerous local brief conductance changes resulting in a transient voltage change at each synaptic site called the post-synaptic potential (PSP). The PSPs from the activated synapses spread in the dendritic tree and summate in the axon to generate there, if a certain depolarized voltage threshold is reached, the output in the form of a train of spikes. The morphology of most dendrites seems to be rather fixed in the mature brain; however, their electrical properties continuously change in an activity-dependent manner. Indeed, when many synapses bombard the dendritic tree, as is the case in the living behaving brain, then the dendritic membrane becomes more leaky due to the conductance increase at each synaptic site and, thus, the electrical length of the dendrites (which reflects the degree of voltage attenuation in the tree) increases. The more enhanced the synaptic input is (in number or in frequency), the more electrically long the dendritic tree becomes. Therefore, the dendritic tree is a dynamical input-output electrical device whose electrical length, as well as its effective membrane tim