Introduction to Muscle Tissue
The three types of muscle tissue share the following common characteristics:
- Contractility – muscles cells shorten to create tension, allowing for movement
- Excitability – muscle cells can be stimulated (excited) and respond by generating tension
- Extensibility – muscle cells can stretch beyond resting length without tearing
- Elasticity – muscle cells can recoil back to their original length after stretching
This chapter will introduce the three types of muscle tissue: skeletal, cardiac, and smooth muscle.
Skeletal Muscle Tissue
Skeletal muscle tissue is responsible for moving our skeleton, supporting our joints, and helping us express emotions through facial expression. Skeletal muscle cells are incredibly long cells, so long that they are referred to as muscle fibers. Skeletal muscle tissue is made of elongated (long) cylindrical-shaped cells. Each cell contains many nuclei, so they are called multinucleated (Figures 1 and 2). The nuclei are peripherally-located, which means they are pushed against the inside of the plasma membrane. Skeletal muscle tissue is striated, a term that refers to its perpendicular “striped” appearance (the sarcomere is cool and we will learn more about it later!). Contraction of skeletal muscle tissue is under voluntary control, meaning that you have conscious control over your skeletal muscle movements.
Table 1: Skeletal muscle
| Tissue Type | Skeletal Muscle |
|---|---|
| General Description | Very long cells that are multinucleated and have visible striations |
| Location | Skeletal muscles of the body |
| Function | Move skeleton and support joints |
| Voluntary or Involuntary? | Voluntary |
| Helpful Hints | Look for the striations and multiple nuclei pushed against the cell membrane |
Figure 1: Skeletal muscle (longitudinal section) with and without illustration overlay
Figure 2: Skeletal muscle (longitudinal and cross section) with and without illustration overlay
Check out our YouTube video to help you understand skeletal muscle:
YouTube Video – Skeletal Muscle Tissue
We will discuss skeletal muscle in greater detail in a later chapter: Skeletal Muscle Tissue and the Neuromuscular Junction
Cardiac Muscle Tissue
Cardiac muscle tissue is found in our heart, and is responsible for the pumping movement of blood throughout our body. Cardiac muscle cells are branched, and connected to each other through unique connections called intercalated discs, which contain gap junctions and desmosomes (Figures 3 and 4). Typically, cardiac muscle cells have one larger, centrally-located nucleus (uninucleated). Cardiac muscle tissue is also striated, which refers to the perpendicular “striped” appearance. Contraction of cardiac muscle tissue is involuntary, meaning that you cannot consciously control contraction of your heart.
Table 2: Cardiac muscle
| Tissue Type | Cardiac Muscle |
|---|---|
| General Description | Shorted branched cells with one nuclei and have visible striations, cells connected by intercalated discs |
| Locations | Heart |
| Functions | Pump blood through the body |
| Voluntary or Involuntary | Involuntary |
| Helpful Hints | Look for the striations and the intercalated discs |
Figure 3: Cardiac muscle (version A) with and without illustration overlay
Figure 4: Cardiac muscle (version B) with and without illustration overlay
Check out our YouTube video to help you understand cardiac muscle:
YouTube Video – Cardiac Muscle Tissue
Smooth Muscle Tissue
Smooth muscle tissue is found in the walls of our hollow organs: blood vessels, trachea/bronchi, intestines, urinary bladder and ureters, uterus, etc. Contraction of smooth muscle tissue squeezes these hollow organs to decrease the diameter of the inside space. In a blood vessel, smooth muscle contraction causes the blood vessel lumen (inside space) to become more narrow, which can decrease blood flow. In your intestines, smooth muscle contraction causes food to mix, and move through your digestive system. In the urinary bladder, smooth muscle contraction causes urine to flow more quickly.
Smooth muscle cells are smooth, which means they are not striated (Figure 5). Smooth muscle cells are uninucleated, small cells that have tapered ends (imagine a feather pillow, which is bulged in the center and skinny on the ends). Contraction of smooth muscle tissue is involuntary, meaning you cannot consciously control its contraction.
Table 3: Smooth muscle
| Tissue Type | Smooth Muscle |
|---|---|
| General Description | Short cells with one nuclei and tapered at the ends, no striations |
| Locations | Walls of our hollow organs and blood vessels |
| Functions | Allows for movement of substances such as food and blood through the organs/body |
| Voluntary or Involuntary? | Involuntary |
| Helpful Hints | Students often confuse this tissue with dense regular connective tissue, the smooth muscle will have more nuclei located in the center of the cells |
Figure 5: Smooth muscle with and without illustration overlay
Check out our YouTube video to help you understand smooth muscle:
YouTube Video – Smooth Muscle Tissue
Chapter Illustrations By:
Georgios Kallifatidis, Ph.D.
cell that contains many nuclei
located to the outside (peripheral)
perpendicular "striped" appearance of skeletal and cardiac muscle cells
under concious control - you can actively choose to move your skeletal muscles
branched cells will resemble the letter Y. A branched cell may connect to one cell on one end, but two cells on the other end.
specialized cell-to-cell connections in cardiac muscle tissue containing gap junctions and desmosomes
cell junction that allows passage of ions from the cytoplasm of one cell to the cytoplasm of the neighboring cell. The flow of ions allows cardiac muscle tissue to communicate electrically.
cell junction that allows tissues to resist pulling and tearing
containing a single (1) nucleus
under sub-concious control, occurs without you thinking about it.
the interior of a tube-shaped organ, like a blood vessel, kidney tubule, or intestines
