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

2. 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.

3. 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.

4. 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.

5. 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.

6. 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?

7. 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.

8. 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.

9. 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?

10. 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.

11. 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.

12. 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.

13. 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

14. 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

15. 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