| MadSci Network: Neuroscience |
Much of the following information is from a lecture by Dr Kilburn of Old Dominion University http://www.lions.odu.edu/~kkilburn/441_lectures/Ch_6.pdf Roeder’s theory is that animal nervous systems are organized into command centers. A command center is a unit of the nervous system that could include a variety of components, such as innate releasing mechanisms, pattern generators, song control. He found ganglia (clusters of nerves) in each body segment suggesting that they controlled muscles of each segment and presumed these to be the command centers. He confirmed this by experimental evidence from cutting connections and stimulating isolated ganglia. There are many examples of these innate, continuously firing circuits of neurons in the body – animals continuously respire, digest, pump blood and so on. These command centers are interconnected via a hierarchy of inhibitory relationships: activating one inhibits the other. Roeder found that some brain cells were responsible for inhibiting activity in abdominal ganglia – preventing muscles from acting until “ordered” to do so by other command centers in brain. He showed that the protocerebral ganglion (brain) typically inhibits abdominal ganglia, suppressing muscle activity. Thus cutting off the insect’s head stops the inhibition and the abdominal ganglia continues its innate pattern of firing moving the limbs attached to its segment. These circuits are able to fire continuously as one of the activating (output) neurons is connected to an excitatory (input) neuron forming a feedback loop. At the synapses and neuromuscular junctions neurotransmitters are synthesized, used and broken down by enzymes in the usual way.
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