This is the 2007 version. Click here for the 2017 chapter 02 table of contents.

Weak Electrical Interactions and Local Circuits

The classical neuron doctrine said a neuron communicated with other neurons by firing nerve impulses when it was pushed over threshold. Each neuron was said to be a little on/off switch, activated only when it received inputs from many other neurons. But modern findings reveal that neurons are not on-off switches. Some neurons conduct all their business with weak electrical interactions. They never fire nerve impulses.

How do weak electrical interactions contradict the classic doctrine?

What are local circuits?

Weak electrical influences are important in dendrodendritic synapses, where distances are so small that there is no room for nerve impulses to travel. Dendrodendritic synapses often form local circuits : tiny areas, only a few microns (millionths of a meter) across, where branches of dendrites from several cells may interact with each other.

Local circuits are so small that one could fit a thousand inside the dot of an exclamation mark. These circuits are not rare, or confined to exotic non-human creatures. During the quiet revolution researchers discovered that the human brain has more local circuits per cubic centimeter than any other brain studied (Schmidt, Dev & Smith, 1976).

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