Storage and recovery of elastic potential energy powers ballistic prey capture in toads
2006
SUMMARY Ballistic tongue projection in toads is a remarkably fast and powerful
movement. The goals of this study were to: (1) quantify in vivo power
output and activity of the depressor mandibulae muscles that are responsible
for ballistic mouth opening, which powers tongue projection; (2) quantify the
elastic properties of the depressor mandibulae muscles and their series
connective tissues using in situ muscle stimulation and force-lever
studies; and (3) develop and test an elastic recoil model, based on the
observed elastic properties of the depressor mandibulae muscles and series
connective tissues, that accounts for displacement, velocity, acceleration and
power output during ballistic mouth opening in toads. The results demonstrate
that the depressor mandibulae muscles of toads are active for up to 250 ms
prior to mouth opening. During this time, strains of up to 21.4% muscle
resting length ( ML ) develop in the muscles and series connective
tissues. At maximum isometric force, series connective tissues develop strains
up to 14% ML , and the muscle itself develops strains up to 17.5%
ML . When the mouth opens rapidly, the peak instantaneous power output
of the depressor mandibulae muscles and series connective tissues can reach
9600 W kg –1 . The results suggest that: (1) elastic recoil of
muscle itself can contribute significantly to the power of ballistic
movements; (2) strain in series elastic elements of the depressor mandibulae
muscle is too large to be borne entirely by the cross bridges and the
actin–myosin filament lattice; and (3) central nervous control of
ballistic tongue projection in toads likely requires the specification of
relatively few parameters.
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