Ronald A. Bergman, Ph.D., Adel K. Afifi, M.D., Paul M. Heidger,
Peer Review Status: Externally Peer Reviewed
Bovine heart, 10% formalin, H. & E.; A. 96 x; B. 240 x.
In this plate, the continuation of the bundle of His*, composed of small unbranched cardiac fibers, is seen in the form of Purkinje* fibers. These large cardiac fibers ultimately join and regulate the contractile activity of ordinary cardiac muscle fibers.
The plate illustrates distinctive features of Purkinje fibers: (1) they are larger than ordinary cardiac fibers and bundle fibers; (2) they may be binucleate, have few myofibrils, and have a vacuous cytoplasm (normally filled with glycogen); and (3) they have a subendocardial location. Purkinje cells have been shown to be linked to bundle fibers and to ordinary cardiac fibers by gap junctions and desmosomes. Gap junctions have been shown to provide a point of electrical, but not protoplasmic, continuity between cardiac fibers and between smooth muscle fibers.
*His, Jr. was a nineteenth-century German physician and Purkinje was a nineteenth-century Bohemian anatomist.
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