Control mechanisms involved in the regulation of the phallic neuromuscular system of the cockroach Periplaneta americana

1. According to their diameter, the axons composing the phallic nerve of the cockroach can be divided into three groups: 5-7 μ, 2-3 μ and 1 μ or less. 2. The large axons probably correspond to excitatory axons, and the small ones to sensory axons. 3. Intracellular recordings from muscles 1-4 were made. M₁, M₂ are innervated by three excitatory axons, M₃ by two, and M₄ only by one. 4. The epsp's induced by the different axons are quite similar, showing rise times of 2-4 msec and half decay times of 7-20 msec. At high frequency they show facilitation and summation. 5. Mepp's were recorded from the muscles. They vary in amplitude and time constant of decay. No correlation between the number of excitatory axons innervating each muscle and mean mepp frequency was observed. 6. Stimulation of the intact phallic nerve with such stimulus intensity as to activate the small axons, induced delayed epsp's in the muscles. The delayed responses disappeared after the phallic nerve was disconnected from ganglion A6. 7. Intracellular recordings from phallic motorneurons, interneurons and unidentified neurons located in ganglion A6, were made. 8. The phallic motorneurons receive excitatory and inhibitory pathways from the ipsi- and contralateral connectives, excitatory and inhibitory pathways from the sensory axons in the ipsi- and contralateral phallic nerves, and excitatory inputs from the cereal nerves. 9. The inputs to the phallic motorneurons are possibly through interneurons. The phallic interneurons receive excitatory inputs from the abdominal connectives and from the phallic sensory axons. 10. Unidentified neurons receive inhibitory inputs from the abdominal connectives. 11. Contralateral inhibition between left and right phallic motorneurons is demonstrated.