Patterns of Circular And Radial Mantle Muscle Activity in Respiration and Jetting of the Squid Loligo Opalescens

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Abstract
By simultaneously recording the electromyographic (EMG) activity of squid mantle muscles, changes in mantle cavity pressure and changes in mantle diameter, we have been able to distinguish the pattern of radial muscle activity from circular muscle activity, and in so doing were able to determine the functional role of these muscle groups in motor behaviours. Three distinguishable phases of activity appear during escape jets : (i), hyper-inflation brought about by the contraction of the radial muscles; (ii), the jet powered by the contraction of circular muscles; and (iii), refilling powered largely by the elastic recoil of the mantle wall, but with a small contribution from the radial muscles. Two distinctly different patterns of muscular activity were seen in respiratory movements. One pattern (pattern I) is powered by the radial muscles alone, while the other (pattern II) is powered by the circular muscles alone. In both modes of respiration, the muscles are apparently antagonized by tissue elasticity. Thus, the storage of elastic energy in the connective tissue fibre-lattice of the mantle wall plays a very important role in both modes of squid movement.

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