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Chapter 8 Muscular System

Chapter 8 Muscular System. 8.1 and 8.2. 8.1. Introduction. Introduction. Muscles = organs composed of specialized cells that use the chemical energy stored in nutrients to contract Purpose All movement Muscle tone Propel body fluids and food Generate the heartbeat Distribute heat. 8.2.

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Chapter 8 Muscular System

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  1. Chapter 8Muscular System 8.1 and 8.2

  2. 8.1 Introduction

  3. Introduction • Muscles = organs composed of specialized cells that use the chemical energy stored in nutrients to contract • Purpose • All movement • Muscle tone • Propel body fluids and food • Generate the heartbeat • Distribute heat

  4. 8.2 Structure of a Skeletal Muscle

  5. Connective Tissue Coverings Fascia Aponeuroses • A sheet of fibrous connective tissue that encloses and muscle • Sheets of connective tissue that attach muscles

  6. Connective Tissue Coverings • 3 layers of connective tissue • Epimysium – closely surrounds the skeletal muscle • Perimysium – extend inward and form compartments containing bundles of muscle fibers called fascicles • Endomysium – thin layer covering each muscle fiber

  7. Connective Tissue Coverings

  8. Skeletal Muscle Fibers • Skeletal muscle fiber = a single cell that contracts in response to stimulation and then relaxes when stimulation ends • Sarcolemma = muscle cell membrane • Sarcoplasm = muscle cell cytoplasm • Muscle cells are multinucleate (have many nuclei)

  9. Skeletal Muscle Fibers • Myofibrils = contractile fibers in muscle cells • Consist of 2 types of protein filaments • Myosin (thick filaments) • Actin (thin filaments) • Alternation of these two filaments produces striations (dark and light bands)

  10. Skeletal Muscle Fibers • Sarcomere = the structural and functional units of a myofibril

  11. Skeletal Muscle Fibers • I band – light bands of thin actin • H zone – only thick myosin filaments • A band – dark bands where actin and myosin overlap • Z line – attaches actin • M line – proteins that hold myosin in place

  12. Skeletal Muscle Fibers • Sarcoplasmic reticulum = membranous network of channels and tubules of a muscle fiber (corresponds to endoplasmic reticulum) • Transverse (T) tubules = membranous channels that extend inward from a muscle fiber membrane (contain extracellular fluid) • Cisternae = enlarged portions of the sarcoplasmic reticulum • A triad is composed of transverse tubules in between two cisternae

  13. Skeletal Muscle Fibers

  14. Neuromuscular Junction • Motor neurons = neurons that control effectors (including skeletal muscle) • Each muscle fiber is functionally, but not physically, connected to a motor neuron • The connection between the motor neuron and the muscle fiber is called a neuromuscular junction.

  15. Neuromuscular Junction • Neurons communicate with muscle cells by releasing chemicals (neurotransmitters) • The functional connection is called a synapse • The motor end plate is the specialized part of a muscle fiber membrane at the neuromuscular junction (abundant nuclei, mitochondria, and folding)

  16. Motor Units • A muscle fiber only has a single motor end plate, but one motor neuron may connect to many muscle fibers • A motor unit is a motor neuron and its associated muscle fibers

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