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J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2007 Dec;193(12):1205-19. Epub 2007 Nov 7.

Muscle function in animal movement: passive mechanical properties of leech muscle.

Author information

1
Department of Biology, University of Virginia, Charlottesville, VA 22904-4328, USA.

Abstract

We investigated passive properties of leech body wall as part of a larger project to understand better mechanisms that control locomotion and to establish mathematical models that predict such dynamical behavior. In tests of length-tension relationships in 2-segment-long preparations of body wall through step-stretch manipulations (step size = 1 mm), we discovered that these relationships are nonlinear, with significant hysteresis, even for the relatively small changes in length that occur during swimming. We developed a mathematical model comprising three nonlinear springs, two in series with nonlinear dashpots that describe well the tension statics and dynamics for step-stretch experiments. This model suggested that body wall dynamics are slow enough to be neglected when predicting the tension generated by imposed sinusoidal length changes (about +/-10% of nominal) at 1-3 Hz, mimicking swimming. We derived a static model, comprising one nonlinear spring, which predicts sinusoidal data accurately, even when preparations were exposed to serotonin (0.1-10 microM). Preparations bathed in saline-serotonin had significantly reduced steady-state and peak tensions, without alterations in tension dynamics. Anesthetizing preparations (8% ethanol) reduced body wall tension by 77%, indicating that passive tension in the obliquely striated longitudinal muscles of leeches results primarily from a resting tonus.

PMID:
17987298
DOI:
10.1007/s00359-007-0278-y
[Indexed for MEDLINE]

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