The Network Within: Signaling Pathways

In the preceding chapters, we have taken the building blocks for neuronal models in the form of ion channels, membrane compartments and synapses (Chapters 4, 5 and 6) and put them together to form neurons, small neural circuits, and then networks (Chapters 7, 8 and 9). We conclude this section of the book by opening the lid on the building blocks, and seeing what happens inside them. There used to be a view of the atom as a tiny solar system, which led to exotic visions of an infinite series of ever-decreasing worlds as one examined matter at finer and finer scales. Neurobiology now has to face a similar unsettling concept: that hidden within “atomic” compartments and under all the ion channels, there exists a whole new universe of subcellular networks. These networks, of course, are the multitudes of interacting biochemical signaling pathways. They profoundly affect everything from the properties of single channels to the morphology of neurons and the wiring of the brain itself. Recent work on biochemical signaling reactions has emphasized the sheer complexity of these networks. There are dozens of known major signaling pathways, each having at least five to ten enzyme isoforms, each of which communicates with a different subset of other messengers and pathways. As with neuronal networks themselves, these biochemical networks cannot be analyzed in isolation. Neuronal signaling events from above, and nuclear and metabolic events from below, provide a barrage of signals that this network must process.

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