University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

163

Pages:

1
Author:

Mariam A. A.

Cardiac muscle • Cardiocytes are branched cylinders 85 to 250 µm long o ~5-10 µm in diameter o 2 nuclei • T tubules envaginate the cardiocyte at the level of the Z-line (as opposed to NMJ in striated) External calcium in surrounding fluid helps contraction (on top of sarcoplasmic reticulum) Cells are joined end to end by specialized junctional complexes called intercalated disks. Intercalated disks have a steplike arrangement, with transverse portions that run perpendicular to the long axis of the cell and longitudinal portions running in parallel to the myofibrils. The transverse component is represented by the Z disk and consists of (1) desmosomes, which mechanically link cardiac cells, and (2) fasciae adherentes, which contain alpha-actinin and vinculin and provide an insertion site for the actin-containing thin filaments of the last sarcomere of each cardiocyte. Gap junctions, restricted to the longitudinal portion of the intercalated disk, enable ionic communication between cells leading to synchronous muscle contraction. The terminal fibers of the conducting system of the heart are specialized, glycogen-rich Purkinje fibers. Compared with the contractile fibers, Purkinje fibers are larger, palerstained, and contain fewer myofibrils. • • • • •