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

Gap Junctions

In the classic neuron doctrine, neurons communicated by chemical means. During the quiet revolution, it was discovered that some neurons were directly connected. These connections are called gap junctions or electrotonic (not "electronic" but "electrotonic") synapses. They are synapses without transmitter substances. At these locations, a nerve impulse is passed immediately to the next neuron through gaps in the membranes.

What is a distinctive characteristic of gap junctions? Where are they commonly found?

These synapses are extremely fast. There is no synaptic delay caused by chemical transmitters going across a synaptic cleft. Thus they are often found in escape systems where they help trigger quick getaway movements. Gap junctions are especially common in fish and invertebrates (animals without backbones). They also exist in the retina of the human eye, where speed of processing is at a premium.

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