ISSN:
1432-136X
Keywords:
Key words Contraction
;
Heart
;
Ostium
;
Homarus americanus (Crustacea)
;
AbbreviationEPSP excitatory postsynaptic potential
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Abstract “Venous” blood enters the crustacean heart through bivalved ostia. Each ostium is a discrete anatomical unit that remains functional even when isolated from the heart. Muscle fibers produce overshooting action potentials that have a plateau of variable duration in response to nervous drive from the cardiac ganglion or during trains of electrical stimuli. Contractions show summation and facilitation when stimulated by trains of stimuli delivered at rates greater than 0.5 s−1 and 0.2 s−1, respectively. Contraction amplitude increases with stimulating impulse frequency and train duration. Maximum force occurs at 1.2 times the slack length. The morphology of ostial fibers resembles that of myocardial fibers. Interconnected bundles of myofilaments occur in both the ostial fibers and the myocardial fibers. In ostial and myocardial fibers, the myofilament bundles are invested by perforated sheets of sarcoplasmic reticulum, and these sheets interface with a network of sarcolemmal tubules to form dyadic interior couplings at the level of the sarcomeric H-bands. The contractile apparatus originates and terminates at intermediate junctions on the transverse cellular boundaries, and the lateral surfaces of the muscle fibers are linked by a modest number of communicating (gap) junctions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s003600050252
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