2-6-2. Overview of Muscle Tissues
Muscle is one of the four primary tissue types of the body, and the body contains three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle (Figure 1). All three muscle tissues have some properties in common; they all exhibit a quality called
The Three Types of Muscle Tissue
The muscles all begin the actual process of contracting (shortening) when a protein called actin is pulled by a protein called myosin. This occurs in striated muscle (skeletal and cardiac) after specific binding sites on the actin have been exposed in response to the interaction between calcium ions (Ca++) and proteins (troponin and tropomyosin) that “shield” the actin-binding sites. Ca++ also is required for the contraction of smooth muscle, although its role is different: here Ca++ activates enzymes, which in turn activate myosin heads. All muscles require adenosine triphosphate (ATP) to continue the process of contracting, and they all relax when the Ca++ is removed and the actin-binding sites are re-shielded.
A muscle can return to its original length when relaxed due to a quality of muscle tissue called
Differences among the three muscle types include the microscopic organization of their contractile proteins—actin and myosin. The actin and myosin proteins are arranged very regularly in the cytoplasm of individual muscle cells (referred to as fibers) in both skeletal muscle and cardiac muscle, which creates a pattern, or stripes, called striations. The striations are visible with a light microscope under high magnification (see Figure 1).
Because the actin and myosin are not arranged in such regular fashion in
Muscle is the tissue in animals that allows for active movement of the body or materials within the body. There are three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle. Most of the body’s skeletal muscle produces movement by acting on the skeleton. Cardiac muscle is found in the wall of the heart and pumps blood through the circulatory system.
Smooth muscle is found in the skin, where it is associated with hair follicles; it also is found in the walls of internal organs, blood vessels, and internal passageways, where it assists in moving materials.
Muscle that has a striped appearance is described as being ________.
Which element is important in directly triggering contraction?
Which of the following properties is not common to all three muscle tissues?
Critical Thinking Questions
Why is elasticity an important quality of muscle tissue?
It allows muscle to return to its original length during relaxation after contraction.