. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CO-ACTIVATION OF ANTAGONISTIC MOTONEURONS 245. Figure 5. (A, B) Morphology of CAB neurons revealed by carboxyfluorescein injections. A single arrow shows the position of the cell bod\ of neuron RCAB. Double arrows show the paracerebral connective: cer— cerebral ganglion, ped—pedal ganglion, int—intestinal ganglia. their reaction depends only on the speed of muscle con- traction. This raises the interesting question of how the Clione buccal cones, which are hydrostatic structures, ex- pand at a rate that is within the range o
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CO-ACTIVATION OF ANTAGONISTIC MOTONEURONS 245. Figure 5. (A, B) Morphology of CAB neurons revealed by carboxyfluorescein injections. A single arrow shows the position of the cell bod\ of neuron RCAB. Double arrows show the paracerebral connective: cer— cerebral ganglion, ped—pedal ganglion, int—intestinal ganglia. their reaction depends only on the speed of muscle con- traction. This raises the interesting question of how the Clione buccal cones, which are hydrostatic structures, ex- pand at a rate that is within the range of muscular elon- gation. We propose here that co-activation of functionally reciprocal A and B motoneuron groups, which evoke pro- traction and retraction of buccal cones respectively, is critical for their rapid and powerful extrusion. The time of Clione buccal cone expansion depends on the time required for synchronizing the activities of all muscles involved in producing this reaction, and on the time required for moving hemocoelic fluid into the cone cavities. The first factor, synchronization, is a problem because buccal cone expansion requires the contraction of many muscle groups, including head wall muscles, neck muscles, circular muscles of buccal cones, and muscles opening the skin folds. Twenty-six A motoneurons whose activity evokes contraction of these muscles have been identified in the cerebral ganglia of C//om?(Norekian and Satterlie. 1993). Synchronized activity of all A neurons is required for initiating buccal cone extrusion. One second of co-activation observed in A and B motoneurons prior to buccal cone inflation would give time for synchroni- zation of activities of all A neurons and all muscle groups participating in this reaction. The second problem is the necessity to eject hemocoelic fluid into cone cavities as rapidly and forcefully as possible. Two factors appear to contribute to resolving this problem. First, Hermans and Satterlie (1992) demon
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
