Which statement about smooth muscle is true?

The muscular system is composed of specialized cells called muscle fibers. Their predominant function is contractibility. Muscles, attached to bones or internal organs and blood vessels, are responsible for movement. Nearly all movement in the body is the result of muscle contraction. There are three different types of muscle tissues in the human body: cardiac, smooth, and skeletal muscle tissues. All three types consist mainly of muscle fibers, but the fibers have different arrangements. Cardiac muscle is found only in the walls of the heart. It is striated, or striped, because its muscle... Show more

The muscular system is composed of specialized cells called muscle fibers. Their predominant function is contractibility. Muscles, attached to bones or internal organs and blood vessels, are responsible for movement. Nearly all movement in the body is the result of muscle contraction.

There are three different types of muscle tissues in the human body: cardiac, smooth, and skeletal muscle tissues. All three types consist mainly of muscle fibers, but the fibers have different arrangements. Cardiac muscle is found only in the walls of the heart. It is striated, or striped, because its muscle fibers are arranged in bundles. Contractions of cardiac muscle are involuntary. This means that they are not under conscious control. When cardiac muscle contracts, the heart beats and pumps blood. Smooth muscle is found in the walls of other internal organs such as the stomach. It isn't striated because its muscle fibers are arranged in sheets rather than bundles. Contractions of smooth muscle are involuntary. When smooth muscles in the stomach contract, they squeeze food inside the stomach. This helps break the food into smaller pieces. Skeletal muscle is attached to the bones of the skeleton. It is striated like cardiac muscle because its muscle fibers are arranged in bundles. Contractions of skeletal muscle are voluntary. This means that they are under conscious control. Whether you are doing pushups or pushing a pencil, you are using skeletal muscles. Skeletal muscles are the most common type of muscles in the body. Many skeletal muscles are attached to the ends of bones where they meet at joints. The muscles are attached to the bones by tough bands of connective tissue called tendons. When the muscles contract, they pull on the tendons, which pull on the bones in turn, causing them to move. Muscles can only contract. They can't actively lengthen. Therefore, to move bones back and forth at joints, skeletal muscles must work in pairs. For example, the biceps and triceps muscles of the upper arm work as a pair. When the biceps muscle contracts, it bends the arm at the elbow. When the triceps muscle contracts, it straightens the arm.

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