Muscle Types

A muscle is an organ that can contract in a coordinated fashion and includes muscle tissue, blood vessels, nerves, and connective tissue. Some of the major muscles of the human body are shown in Figure 45-9. Recall that the human body has three types of muscle tissues: skeletal, smooth, and cardiac.

Skeletal muscle is responsible for moving parts of the body, such as the limbs, trunk, and face. Skeletal muscle tissue is made up of elongated cells called muscle fibers. Each muscle fiber contains many nuclei and is crossed by light and dark stripes, called striations, as shown on the following page in Figure 45-10a. Skeletal muscle fibers are grouped into dense bundles called fascicles. A group of fascicles are bound together by connective tissue to form a muscle. Because their contractions can usually be consciously controlled, skeletal muscles are described as voluntary muscles.

Frontalis

Trapezius

Deltoid

Pectoralis major

Triceps brachii

Biceps brachii

Latissimus dorsi

Abdominal muscles

Gluteus maximus

Sartorius Biceps femoris

Rectus femoris Gastrocnemius Achilles tendon

figure 45-9

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