Hopkins Marine Station Student Paper

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(full paper is archived in the Miller Library)

Title: Mechanical properties and possible control mechanisms of non-muscular catch in the spine ligaments of the sea urchin
Student Author(s): Diab, Mohammad
Faculty Advisor(s): Gilly, W. F.
Pages: 35
Location: Final Papers Biology 175H
Date: June 1983
Keywords: echinoderms
Abstract: Spines of sea urchin Strongylocentrotus franciscanus were deflected through varying angles and the resistive forces offered by their ligaments were recorded. Data obtained for spines out of cathc and spines in catch show basic differences in shape as well as amplitude. This difference in shape was also observed in the data obtained for different spines in catch. The contractile force of the muscle layer at the base of the sea urchin spines was determined and found to significant in comparison to the resistive upon 10 degrees deflection offered by the spine ligaments when in a state of catch. A survey of a poulation of spines, both agitated and non-agitated, was conducted to obtain an objective definition of the state of catch vs. non-catch. An angular limit to deflection was found to exist for spines in catch, beyond which their ligaments would become irreversibly damaged. Experimental and mathematical calculation fo Young's Modulus was done for a spine ligament in catch, and this was found to be similar to that given for vertebrate tendon at the same strain. The relationship between resistive force offered and angular deflection was exmained, and it was found to be non-linear. The possibility of nervous control of catch was considered, although results obtained make this seem unlikely. That the setting of catch is Ca+2 dependent was here confirmed. Furthermore, the reversibility of the effects of Ca2+ depletion were confirmed, although the process of reversla remains unclear, for recovery time was found to be very long. The effects of protein inhibitors on catch were also studied, and the preliminary results provide strong evidence for an enzymatic mechanism in teh control of catch.