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Types of Muscle Tissue: Skeletal, Cardiac & Smooth

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  • 0:58 Muscle histology
  • 3:12 Muscular contraction
  • 5:10 Regulation of contraction
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Lesson Transcript
Instructor: John Simmons

John has taught college science courses face-to-face and online since 1994 and has a doctorate in physiology.

Have you ever wondered why muscle has different names such as striated, smooth, voluntary, or involuntary? This lesson describes the different types of muscle tissue based on their histology, mechanism of contraction, and regulation.

Muscle Tissue

The three types of muscle tissue.
Muscle Tissue Types

Muscle is one of four different tissues found in our bodies. The other general tissue types include epithelial tissue, connective tissue, and nervous tissue. Specifically, we have three different types of muscle tissue, including skeletal, cardiac, and smooth. Each type of muscle is unique in terms of its structure and its function. Regardless of the specific type, all muscle serves the same general function, and that is support and movement. In other words, muscles contract, thus causing the body and body parts to move. In this lesson, we will compare and contrast the three different muscle types in terms of their structure and function.

Muscle Histology

Tissues are made of cells, and a muscle cell is referred to as a myocyte or sometimes simply a muscle fiber because some are long and they look like a fiber. Let's first compare muscle tissue based on what you would see under a microscope; that is, its histology.

Both cardiac and skeletal muscle are termed striated muscle, as they have striations that run across their muscle fibers. In contrast, smooth muscle is not striated, and it's, well, smooth. The striations are end-to-end junctions of repeating units that are referred to as sarcomeres. A sarcomere is a functional unit of striated muscle, as it contains all the tools necessary for contraction. In this sense, you can think of a smooth muscle as a giant sarcomere. Skeletal and cardiac muscle, while both striated, can be distinguished based on arrangement of the fibers. While skeletal muscle fibers are long and linear, cardiac muscle fibers are short and branched.

Looking at skeletal muscle with a microscope, we can see the fibers stacked neatly together in a parallel arrangement. Additionally, these fibers are long, and they run the entire length of the muscle organ. I guess this is what my mother expected my room to look like - nice and orderly.

Skeletal muscle under a microscope
skeletal muscle under microscope

Cardiac muscle, on the other hand, looks more like my kid's room - a complete mess. As the myocytes are branched, they run in different directions as they interconnect with one another. Additionally, cardiac fibers are connected end-to-end with each other with special structures called intercalated discs. The intercalated discs, like the striations separating the sarcomeres, run across the fibers. However, they appear darker on the slide, and they allow for direct communication between the adjacent myocytes.

Cardiac muscle myocytes run in different directions.
Cardiac Muscle Structure

Smooth muscles have a characteristic spindle shape.

Smooth muscle has a spindle shape.
smooth muscle

Muscular Contraction

Skeletal muscle tissue is found in our skeletal muscles; for example, the biceps. Cardiac muscle is found in our heart, and smooth muscle is found in our visceral, or hollow, organs - for example, blood vessels and intestines. All muscles contract as a result of interaction between special proteins within the myocytes. Skeletal, cardiac, and smooth muscle cells synthesize the contractile proteins actin and myosin, which are needed for muscular contraction.

When the muscle cell is stimulated, actin and myosin interact in such a way to cause the cell to shorten and, thus, the muscle to contract. Furthermore, all muscles contract in response to intracellular calcium. In striated muscle, calcium binds to a regulatory protein called troponin, which allows actin and myosin to interact with each other. In smooth muscle, calcium binds to the regulatory protein calmodulin, which allows the contractile proteins to interact and, thus, the muscle to contract.

Actin and myosin interact during muscle cell stimulation, causing muscle contractions.
Muscular Contraction

Where does the calcium come from? In skeletal muscle, the calcium is released from internal stores that we call sarcoplasmic reticulum. Cardiac and smooth muscle contraction is dependent upon extracellular calcium in addition to the intracellular calcium from the sarcoplasmic reticulum.

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