Chapter 12 The Skeleton and Muscles

Section 12-1 Structure and Function of the Human Skeleton Bones serve many functions and play an important role in homeostasis. Bones Provide internal support. Allow for movement. Help protect internal body parts. Produce blood cells and platelets. Store fat. Help regulate blood calcium levels.

The human skeleton consists of two parts: Section 12-1 The human skeleton consists of two parts: The axial skeleton The appendicular skeleton

Section 12-1 All bones have a hard, dense outer layer that surrounds a less compact central region. Inside the bone is the marrow cavity, filled with either fat cells (yellow marrow) or blood cells and blood-producing cells (red marrow) or with combinations of the two. Figure 12-3

Section 12-1 Bones are constantly remodeled in adults to meet changing stresses placed on them. Two cells are responsible for bone remodeling: Osteoclasts—destroy bone Osteoblasts—form bone Bone is a homeostatic organ that helps maintain proper levels of calcium in the body.

The joints permit varying degrees of mobility. Section 12-1 The joints permit varying degrees of mobility. Immovable Slightly movable Freely movable Most of the bones of the human skeleton start out as hyaline cartilage.

Section 12-1 Figure 12-4 Two Immovable Joints

Section 12-1 Figure 12-5 A Slightly Movable Joint

Bone fractures are repaired by fibroblasts and osteoblasts. Section 12-1 Bone fractures are repaired by fibroblasts and osteoblasts. Osteoporosis involves a loss of calcium, which results in brittle, easy-to-break bones. Figure 12-11

Section 12-2 The Skeletal Muscles Skeletal muscles are involved in Body movements Maintenance of posture Production of body heat

Figure 12-13 The Skeletal Muscles Section 12-2 Figure 12-13 The Skeletal Muscles

Section 12-2 Figure 12-13 Figure 12-13 The Skeletal Muscles

Section 12-2 Figure 12-13 The Skeletal Muscles Figure 12-13

Section 12-2 Figure 12-13 Figure 12-13 The Skeletal Muscles

Section 12-2 Skeletal muscle cells are known as muscle fibers and are both excitable and contractile. Muscle fibers contain many small bundles of contractile filaments known as myofibrils. Figure 12-15a,b

Section 12-2 Figure 12-15c-e

Section 12-2 During muscle contraction, the actin filaments slide inward, causing the sarcomeres to shorten. The energy for muscle contraction comes from ATP. ATP is replenished by creatine phosphate, glycolysis, and cellular respiration.

Section 12-2 Individual skeletal muscle fibers contract after being stimulated by an action potential. The strength of muscle contraction can be increased by stimulating (recruiting) additional muscle fibers to contract. Additional tension may be created in a muscle fiber if a nerve impulse arrives while the muscle fiber is still contracted.

Section 12-2 Muscle tone results from the contraction of a small number of muscle fibers that keep muscles slightly tense. Two types of muscle fibers are found in skeletal muscle, slow- and fast-twitch. Fast-twitch fibers are found in greatest number in muscles that perform rapid movement. Slow-twitch fibers are found in muscles that perform slower motions or are involved in maintaining posture.

Exercise builds muscles and increases endurance. Section 12-2 Exercise builds muscles and increases endurance. An increase in muscle mass results from an increase in the amount of contractile protein in muscle fibers. Endurance is a function of at least three factors: the condition of the heart, the condition of the muscles of inspiration, and the blood volume. Improvement in all three factors increases the efficiency of oxygen delivery to muscles.

Section 12-3 Health and Homeostasis Intentional misuse of steroids can cause physical, psychiatric, and behavioral problems.