The distribution of the common inhibitory neuron in brachyuran limb musculature
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In each of the seven muscles controlling the three distal joints of the walking legs ofEriphia, the common inhibitory neuron (CI) was found to innervate most strongly the slowly responding tonic fibers and least strongly or not at all the most rapidly responding phasic fibers.
Within each muscle, the fibers receiving CI occupy consistent locations as determined by electrophysiological mapping.
The distribution of four tonic through phasic fiber types was determined independently by histochemical means. The results agree closely with those obtained electrophysiologically.
In the muscles that receive two excitors in addition to CI (closer, bender, and extensor), a pronounced preferential distribution to tonic fibers was found both for CI and for the slow excitor. The fast excitor affects all fibers strongly; the most phasic fibers are innervated only by it.
In the opener and stretcher muscles, which each receive a specific inhibitor in addition to CI and a single shared excitor, all muscle fibers are innervated by the two inhibitors, although their efficacies differ. The specific inhibitor was found to affect all fibers strongly. CI's synaptic efficacy varies greatly: it exceeds that of the specific inhibitor in some tonic fibers, but is very weak (though always detectible) in the most phasic fibers. CI's effectiveness is similarly distributed in the singly excited and singly inhibited accessory flexor muscle.
In the flexor muscle with its quadruple excitatory innervation, CI and at least one particular excitatory axon again supply tonic fibers preferentially. At least one excitor appears to have a complementary distribution, innervating phasic but not tonic fibers.
KeywordsSpecific Inhibitor Fiber Type Preferential Distribution Limb Musculature Flexor Muscle
excitatory junctional potential
inhibitory junctional potential
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