In the illustration, the longitudinal section of smooth muscle displays long fusiform smooth muscle cells with centrally located, elongated nuclei. Since the muscle fibers are arranged in staggered arrays, they can be packed very closely, with only a limited amount of intervening connective tissue. Each smooth muscle cell is sur rounded by a basal lamina and reticular fibers, neither of which is evident in this figure. Capillaries are housed in the connective tissue separating bundles of smooth muscle fibers.

• The fibers of cardiac muscle are not arranged in a simple parallel fashion. Instead, they branch at the ends to form connections with multiple adjacent cells, resulting in a complex, three-dimensional network.
• Cardiac muscle fibers are long cylindrical cells with one or two nuclei. The nuclei are centrally situated like that of smooth muscle.
• Cardiac muscle sarcoplasm has a great number of mitochondria to meet the energy demands.
• Similar to the skeletal muscle, cardiac muscle cells have an invaginating network

Each muscle cell is defined by a sarcolemma and contains many nuclei along its length. The nuclei are displaced peripherally within a cross section of the sarcoplasm while a large number of longitudinal myofibrils, groups of arranged contractile proteins, occupy most of the center space. The myofibril contains several important histological landmarks:

• The myofibril is composed of alternating bands. The I-bands (isotropic in polarized light) appear light in color and the A-bands (anisotropic in polarized light) appear dark in color. The alternating pattern of these bands results in the striated appearance of skeletal muscle.
• The Z-lines (Zwischenschieben) bisect the I-bands.
• A light band called the H-band (Heller) sits within each A-band.
• The M-line (Mittelschiebe) bisects each A-band (and, in doing so, bisects each H-band).