Meeting Abstract
39.5 Sunday, Jan. 5 09:00 The remarkable properties of the obliquely striated nuchal retractor muscle of squid THOMPSON, J.T.*; LAVALVA, S.; CLARICI, D.; MOORE, M.; Franklin & Marshall College; Franklin & Marshall College; Franklin & Marshall College; University of Maine joseph.thompson@fandm.edu
We investigated the in vivo function and in vitro contractile properties of the nuchal retractor muscle of the Atlantic longfin squid (Doryteuthis pealeii). This muscle, which is actually a muscular hydrostatic organ composed of both longitudinal and radial muscle fibers, functions during jet locomotion to alternately protrude and retract the squid’s head during jet locomotion, and in so doing appears to ensure the appropriate flow of water during the jet cycle. Synchronized sonomicrometry and electromyography records of 21 squid revealed that the muscular organ operates over an impressive range of strains during escape jets, with mean maximum elongations and contractions of +0.26 ± 0.29 and -0.64 ± 0.22, respectively. In addition, the muscular organ operates at impressive strain rates, with mean maximum elongation and contraction strain rates at 15°C of 1.61 ± 1.14 and -5.74 ± 3.8 muscle lengths s-1, respectively. During some of the most vigorous escape jets, we noted a two-stage contraction in which the muscle would shorten rapidly, pause for a few milliseconds, and then shorten even farther. The second phase of contraction was always accompanied by a second burst of EMG activity. In vitro experiments revealed that the longitudinal fibers of the nuchal retractor have the highest maximum unloaded shortening velocity measured for an obliquely striated muscle: 7.0 ± 2.4 lengths per second at 15°C. The longitudinal fibers were able to produce relatively high force over a wide range of muscle preparation lengths. While the left side of the ascending limb of the length-tension curve was relatively linear, force increased in step-wise fashion as preparation length approached L0. Funded by NSF grant IOS-0950827.
