HISTOLOGY REVIEW Muscle Tissue Dr. Tim Ballard Department of Biology and Marine Biology

individual muscle fibers Skeletal muscle Skeletal muscle – longitudinal section – H&E – 10x objective individual muscle fibers nucleus Skeletal muscle fibers (individual cells) are long and cylindrical, with multiple nuclei that are placed on the perimeter of the fibers.

Skeletal muscle Skeletal muscle – longitudinal section – H&E – 20x objective connective tissue and blood vessels between muscle fibers multiple nuclei on the periphery of the cell By moving the fine-focus adjustment gently up and down, you can see the alternating light and dark bands that form the striations.

Skeletal muscle Skeletal muscle – longitudinal section – H&E – 40x objective multiple nuclei on the periphery of the cell connective tissue and blood vessels between muscle fibers individual muscle fiber The striations, peripheral nuclei, and parallel fibers are the selling points that this is skeletal muscle seen in longitudinal section.

Skeletal muscle Human esophagus (upper) – section – H&E – 10x objective longitudinal skeletal muscle fibers See the striations? multiple nuclei on the periphery of the cell See the peripherally-placed nuclei? skeletal muscle fibers in cross section The upper esophagus of the human has skeletal muscle in both cross and longitudinal section.

skeletal muscle fibers in cross section Skeletal muscle – cross section – H&E – 40x objective skeletal muscle fibers in cross section Why can’t you see the striations in a cross-section of skeletal muscle?

Skeletal muscle I band A band I Z Z line Z H zone M line sarcomere Electron micrograph of a skeletal muscle cell in longitudinal section at stages of increasing of contraction.

Cardiac muscle Cardiac muscle – section – H&E – 10x objective Cardiac muscle cells run parallel to one another, but unlike skeletal muscle cells, the individual fibers branch to meet other cells, forming a meshwork or network of cells. Compare this section with skeletal muscle. Look at the lack of parallel organization of the fibers compared to that of skeletal muscle.

Cardiac muscle Cardiac muscle – section – H&E – 20x objective In this view the branching nature of the cardiac muscle cells is more visible. In addition, look at the nuclei. How many are there and where are they?

centrally-located nucleus Cardiac muscle Cardiac muscle – section – H&E – 40x objective striations intercalated disc centrally-located nucleus One distinguishes cardiac muscle from skeletal muscle by the branching fibers, presence of intercalated discs, and centrally-placed single nuclei/cell.

Cardiac muscle Cardiac muscle –section – silver – 20x objective branching intercalated disc nucleus This stain clearly shows the single central nucleus, branching fibers, intercalated discs, and striations.

Smooth muscle Smooth muscle – teased apart – H&E – 20x objective The tapered nature of these cells allows them to be fitted together into sheets of cells, perfect for forming the walls of hollow organs. In addition, the lack of sarcomeres means that the muscle sheets can stretch to accommodate the increased pressure within the organs. Individual cells are long, thin, and tapered on the ends. There is a single nucleus per cell, usually at its longitudinal center. There are no striations.

Smooth muscle Large intestine – longitudinal section – H&E – 10x objective mucosa submucosa muscularis externa inner circular outer longitudinal Circular smooth muscle cells cut longitudinally would look like Longitudinal smooth muscle cells cut longitudinally would look like

inner circular smooth muscle Duodenum – cross section – H&E – 40x objective inner circular smooth muscle Circular smooth muscle cells cut in cross section would look like

Smooth muscle Large intestine – longitudinal section – H&E – 40x objective collagen fibers smooth muscle Contrast the smooth muscle cells with the collagen fibers just above them. end