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UNIT 35

SKELETAL MUSCULAR SYSTEM Learning objectives 1. Learn the makeup of a long bone. 2. Learn the difference in the function of osteoclasts and osteoblasts. 3. Learn the steps that occur in the repair of a broken bone. 4. Learn the ways by which one can reduce the chances of getting osteoporosis. 5. Learn the anatomy and histology of a muscle. 6. Understand what is involved in the contraction of a muscle. Introduction The skeletal and the muscular system operate together to accomplish a variety of functions. Connective tissue plays a valuable role in relating bone to muscle. Although bone contains a large percent of inorganic material, it is living tissue and as such requires proper nutrients. In addition to providing support for the body, the skeletal system provides protection for the brain, spinal nerve and chest organs, and contains the bone marrow, which is responsible for the production of all the various blood cells. The various types of muscle provide locomotion of the individual but also move food and fluids within the body. A. SKELETAL SYSTEM 1. Bone is a type of connective tissue. a. Connective tissue is tissue that has cells embedded in an extracellular matrix. b. Connective tissue functions mainly to bind and support other tissues. c. The matrix in bone is mainly calcium phosphate which hardens into a strong, hard tissue. d. Bone can be compact or spongy (fig. 35.1).

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Figure 35.1 Anatomy of a long bone. A long bone is encased by the periosteum except where it is covered by hyaline (articular) cartilage. Spongy bone located in each epiphysis may contain red bone marrow. The central shaft contains yellow bone marrow and is bordered by compact bone, which is shown in the enlargement ad micrograph. 1) Compact bone is highly organized. a) Bone cells, osteocytes lie in cavities called lacunae. b) The bone is organized into tubular units called osteons. c) There is a central canal in each osteon that carries the blood vessels, lymph vessels, and nerves. d) Small passages, canaliculi run from the central canal to the lacunae and transport nutrients. 2) Spongy bone is much more porous. a) It is lighter than compact bone. b) It often contains red bone marrow which contains the stem cells that give rise to all types of blood cells.

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2. The skeletal system also contains cartilage. a. Cells called chondrocytes are in lacunae embedded in a gelatinous matrix which

contains many fibers. Cartilage is found at the end of long bones between joints, end of ribs, as discs between vertebrae, ear flaps, rings in the trachea, and in the

nose. 3. Fibrous connective tissue makes up the ligaments and tendons. 4. Figure 35.2 shows the arrangement of tissues at an arm joint.

Figure 35.2. Showing the relationship between muscles, bones, and connective tissue of the forearm 5. Examination of a long bone (fig. 35.1) shows its makeup. a. The shaft is the main portion of the bone and is called the diaphysis.

1) It is covered with a layer of connective tissue, periosteum, which is continuous with ligaments and tendons.

2) It is filled with fatty, yellow bone marrow. b. The ends of the long bone are called epiphyses and are composed of spongy bone. c. The ends of the long bone are covered by articular cartilage. 6. In addition to providing support for the muscular system, bone also serves as protection. a. The ribs protect the lungs. b. The skull protects the brain. c. The vertebrae protect the dorsal nerve cord.

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7. Adult bone contains two types of cells. a. Osteoclasts which reabsorb bone matrix are under the control of parathyroid hormone. They will reabsorb bone matrix in order to keep the blood calcium level at the proper level. b. Osteoblasts are bone forming cells, which are under the control of calcitonin from the thyroid. They stimulate the laying down of bone matrix, 8. Bone repair (fig. 35.3) a. A hematoma forms from blood from the canals and periosteum in the space between the broken pieces. Called a procallus. b. A fibrocartilaginous callus is formed. Get an external and internal callus. 1) Initially the external callus consists of cartilage that is formed by chondroblasts. 2) Gradually osteoblasts form a bony callus that knits the ends of the bone together. 3) Stress increases the activity of the osteoblasts and facilitates healing. c. Remodeling 1) During the months that follow the formation of the bony callus, osteoclasts reabsorb the bone of the external callus 2) They also absorb the part of the internal callus that blocks the medullary cavity. 9. Osteoporosis a. Common condition in older people. b. Believed to be the result of a gradual reduction in the rate of bone formation while the rate of bone reabsorption remains normal.

Figure 35.3. Bone fracture and repair.

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c. Causes bones to become porous, fragile, and relatively easily broken. d. Prevention 1) Stress on bones by use of muscles stimulates the cells to lay down bone. 2) Adequate amounts of calcium and vitamin D are necessary. 3) Estrogen replacement therapy will delay onset in women, but there are concerns that it may enhance certain cancers, i.e. breast cancer. B. MUSCLE SYSTEM 1. Relationship of muscles and skeletal system (fig. 35.2) a. Muscles that move the skeletal system are called striated or voluntary muscles. You can control them by conscious effort. b. Muscles that move a joint in opposite directions are referred to as antagonists. 1) One muscle is a flexor; it bends a joint and brings one bone closer to the other. 2) The other muscle is the extensor; it serves to extend a joint and moves one bone away from the other. c. Muscles are attached at two points on bones. 1) The origin is less movable of the two points. 2) The insertion is the more movable of the two points. d. Tendons are composed of a type of connective tissue and attach muscle to bone. e. Ligaments are composed of the same type of connective tissue and attach bone to bone. 2. The size and strength of a muscle depend largely on the number and size of the individual cells, fibers, in the muscle. a. The number of fibers appears to be genetically determined. b. Increase in size of a muscle is due largely to the increase in the protein fibrils within the cells. 3. Fig. 35.4 shows the makeup of a muscle.

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Figure 35.4. Anatomy and histology of a skeletal muscle

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a. The cells are called fibers. b. The fiber is composed of myofibrils. c. The myofibril is composed of two protein filaments. 1) larger filament is myosin 2) smaller filament is actin. d. Muscle contraction (fig. 35.5) 1) An electrical impulse to the muscle causes the membrane of the muscle to become depolarized. 2) This results in a release of calcium ions within the muscle. 3) The calcium ions cause the myosin bridges to contact the actin filaments and swing them inward resulting in shortening of the muscle and contraction. 4) ATP is necessary to break the bridges and let the muscles relax and get the bridges “cocked” for the next contraction.

Figure 35.5. The role of calcium and myosin in muscle contraction. 4. Functions of skeletal muscle. a. Locomotion b. Move blood and lymph

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c. Protect internal organs d. Help maintain body temperature e. Help support body

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UNIT 35

OBJECTIVE QUESTIONS OVER SKELETAL MUSCULAR SYSTEM

1. (A) Bone (B) Cartilage (C) Ligament (D) Tendon (E) Two of the preceding (F) Three of the preceding (G) All the preceding is/are type(s) of connective tissue. 2. Tendons connect (A) bone to bone (B) muscle to muscle (C) muscle to bone. 3. Spongy bone is found in the (A) end of the bone (B) shaft of the bone (C) both A and B. 4. (A) Bone (B) Cartilage (C) Both A and B (D) Neither A or B contain(s) living cells. 5. Chondrocytes are located in (A) bone (B) cartilage (C) tendons. 6. Blood vessels are located in the (A) central canal (B) lacunae (C) canaliculi of the bone. 7. (A) Osteoblasts (B) Osteoclasts (C) Both A and B (D) Neither A or B are bone forming

cells. 8. The first structure to form in the healing of a broken bone is the (A) bony callus (B) hematoma (C) fibrocartilage. 9. Which of the following appear to prevent or delay osteoporosis? (A) Calcium (B) Vitamin D (C) stress on the bone (D) two of the preceding (E) all the preceding. 10. A flexor muscle moves one bone (A) away from the other (B) closer to another. 11. The size and strength of a muscle will be influenced by (A) number of fibers (cells) in the

muscle (B) number of fibrils in each muscle cell (C) proper exercise (D) two of the preceding (E) all the preceding. 12. Muscle contraction depends upon an increase in the ion (A) sodium (B) potassium (C) iron (D) calcium. 13. The larger muscle protein filament is (A) actin (B) myosin. 14. The (A) actin filament (B) myosin filament has molecular bridges. 15. ATP is necessary to (A) “cock” the muscle for its next contraction (B) let the muscle relax by separating actin from myosin (C) both A and B (D) neither A or B.

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DISCUSSION QUESTIONS OVER SKELETAL MUSCULAR SYSTEM

1. Relate cartilage, tendon and ligament to a long bone. 2. List two functions of the skeletal system. 3. What is the difference between compact and spongy bone? a. Structure b. Function 4. What is the function of osteoclasts? 5. List the stages in the healing of a broken bone. a. b. c. 6. List three places in your body where cartilage can be found. a. b. c. 7. Where does the electrical impulse come from that stimulates a muscle? 8. What does it mean to say muscles occur in antagonistic pairs across a joint? 9. What ion is necessary to bring myosin bridges in contact with actin? 10. Do all people have the same number of cells in the same muscle? Explain.

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11. List several functions of skeletal muscle. a. b. c.

CRITICAL THINKING QUESTIONS OVER SKELETAL MUSCULAR SYSTEM

1. What is the reason that today we place a minimum cast or walking cast on a person’s leg when they have a broken bone rather than the heavy much longer cast we used to use?