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A light and electron microscopic study of the heart of a crayfish, Procambarus clarkii (Giraud). II. Fine structure
Author(s) -
Howse Harold D.,
Ferrans Victor J.,
Hibbs Richard G.
Publication year - 1971
Publication title -
journal of morphology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.652
H-Index - 74
eISSN - 1097-4687
pISSN - 0362-2525
DOI - 10.1002/jmor.1051330308
Subject(s) - myofibril , biology , anatomy , basal lamina , biophysics , cytoplasm , myocyte , crayfish , actin , organelle , ultrastructure , electron microscope , cardiac muscle , microbiology and biotechnology , sarcomere , biochemistry , physics , fishery , optics
The adventitia of the crayfish heart is composed of cells that are separated from each other by an intercellular space about 280 Å wide. Desmosomes are present on apposing surfaces of adjacent cells. A basal lamina underlies the adventitia and consists of a dense, amorphous substance that contains numerous fine filaments. The myocardial cells are striated and an external lamina 0.1 μ thick is present on the surface of the plasma membrane. The nuclei and most of the cytoplasm, glycogen and mitochondria are located at the cell periphery. The myofibrils are composed of thick and thin filaments and confined to the core of the cell. A T system and a well‐developed SR are present. Elements of these organelles form dyads at levels that correspond to the H bands, and triads at levels that correspond to the Z bands of the peripheral myofibrils. The relationship of the T tubules to the myofibrils is discussed. Locus cells exhibit a unique pattern of intracellular myofibrillar branching. They branch from a region which has a structure similar to the Z band material. The myofibrils radiate outwardly in various directions and form numerous cellular branches which form intercalated discs with adjacent myocardial cells. These discs are more complex than those observed in poikilothermic vertebrates but are simpler than those in mammals. An endocardium is lacking in the crayfish heart but interstitial cells are present in close association with the myocardial cells and neural elements. Terminal nerve processes deeply embedded in the myocardial cells are described.