STRIATED (CARDIAC) MUSCLE
Slide 15 shows cardiac muscle. Focus on the muscle that is cut in longitudinal section, such as the above photos. The top two photos are from your slide set. Focus up and down and look for striations. Also, look for lines running perpendicular to the muscle fibers. These are intercalated disks and represent specialized junctions that allow for communication between the individual fibers (cells). Find an electron micrograph of an intercalated disk and identify the types of junctions and their functions.
Also note that the nuclei are larger than those in skeletal muscle and they are centrally located. In fact, the fibers may branch around a nucleus. Each cell (fiber) has only one nucleus.
What are the features that distinguish cardiac muscle from skeletal muscle?
Slide 13 shows cells at periphery of the section that are specialized for conduction. These are cardiac muscle cells called "Purkinje fibers". They have scattered sarcomeres (contractile units) and large patches of glycogen. In the above photo, the glycogen has been dissolved in the processing of the section and shows only a clear space. The cells are rounder than the normal cardiac muscle fibers.
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