8 - 1 Chapter 8 Muscular System

Definition:Three Types (definition & example) Functions:Examples : Muscular System (Muscles) - Organs composed of specialized cells that use the chemical energy stored in nutrients to contract. 1-Skeletal – attaches to bones and is under conscious control 2-Smooth – within blood vessels and hollow organs (involuntary) 3-Cardiac – heart (involuntary) Provide forces that move body parts Maintain posture Generate heartbeat Main source of body heat Muscle tone Propel body fluids and food

8 - 3 Introduction: A.All movements require muscle B.Three types of muscle 1. skeletal, smooth, and cardiac muscle. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

8 - 4  Structure of a Skeletal Muscle A.Each muscle is an organ, comprised of skeletal muscle tissue, connective tissues, nervous tissue, and blood. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

8 - 5 B.Connective Tissue Coverings 1.Layers of dense connective tissue, fascia, surround and separate each muscle. 2.This connective tissue gives rise to tendons and are fused to the periosteum of bones. 3.Epimysium - layer around each whole muscle 4. Perimysium - surrounds individual bundles (fascicles) within each muscle 5. Endomysium – covers each muscle cell (fiber) Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

8 - 6 Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

8 - 7 Study Analogy Pretend you are going to play a joke on someone Pretend you are going to play a joke on someone and give them 100 pencils. The pencils will and give them 100 pencils. The pencils will represent muscle fibers. First you wrap each represent muscle fibers. First you wrap each individual pencil in tissue paper (dense tissue paper individual pencil in tissue paper (dense tissue paper of course!). This would be endomysium. Then of course!). This would be endomysium. Then you take about 10 pencils in a bundle (a fascicle) you take about 10 pencils in a bundle (a fascicle) and wrap them in paper (perimysium). After that and wrap them in paper (perimysium). After that you take all the bundles and wrap them in gift wrap (epimysium). But you are going to mail this joke, you take all the bundles and wrap them in gift wrap (epimysium). But you are going to mail this joke, so you also have to wrap it in brown paper so you also have to wrap it in brown paper representing the fascia. representing the fascia.

8 - 8 C. Skeletal Muscle Fibers 1.Single, long, cylindrical muscle cell. 2.Under the sarcolemma (cell membrane) lies sarcoplasm (cytoplasm) the sarcoplasm contains myofibrils. a. Thick filaments of myofibrils are made up of the protein myosin. b. Thin filaments of myofibrils are made up of the protein actin. c. The organization of these filaments produces striations. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

8 - 9 Muscle Striations

A sarcomere extends from Z line to Z line. a.I bands = actin filaments (thin) b.A bands = overlapping thick and thin filaments. c.H zone (center of A bands) = myosin filaments (thick)

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D.Neuromuscular Junction 1.The site where the motor neuron and muscle fiber meet is the neuromuscular junction. E.Motor Units 1. A motor neuron and the muscle fibers it controls make up a motor unit; when stimulated to do so, the muscle fibers of the motor unit contract all at once. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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 Skeletal Muscle Contraction A.Muscle contraction result in the shortening of sarcomeres, and the pulling of the muscle against its attachments. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

B.Role of Myosin and Actin 1.Myosin consists of two twisted strands with globular cross-bridges projected outward along the strands. 2.Actin is a globular protein with myosin binding sites Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

How do muscles contract? 1. Motor neuron releases acetylcholine 2. Acetylcholine binds to receptors on muscle fiber 3. Muscle fiber is stimulated and passes impulse to sarcoplasmic reticulum 4. Ca binds to troponin molecules 5. Troponin and Tropomyosin interact and expose binding sites on actin 6. Actin and Myosin link 7. Myosin pull actin inward 8. Muscle fiber shortens and creates contraction

How do muscles relax? 1. Muscle fiber is destimulated by acetylcholine 2. Ca is transported into sarcoplasmic reticulum 3. ATP breaks links between actin and myosin 4. Troponin and Trypomyosin block binding sites on actin 5. Muscle fiber relaxes 6. ATP breaks down, getting myosin ready for next contraction

C.Stimulus for Contraction 1.The motor neuron must release the neurotransmitter acetylcholine for muscle contraction. D. Energy Sources for Contraction 1. Energy for contraction comes from ATP. 1. Energy for contraction comes from ATP. ATP – Adenosine Triphosphate 2.Creatine phosphate, which stores excess energy is present to regenerate ATP from ADP and phosphate. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

 Skeletal Muscle Actions A.Origin and Insertion 1. The immovable end of a muscle is the origin, while the movable end is the insertion; contraction pulls the insertion toward the origin. 2.Some muscles have more than one insertion or origin. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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B.Interaction of Skeletal Muscles 1.Of a group of muscles, the one doing the majority of the work is the prime mover. 2.Helper muscles are called synergists; opposing muscles are called antagonists. Examples:?? Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Muscle Movement

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