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Understanding the Muscular System: Structure and Function

Explore the anatomy and physiology of skeletal muscles, from muscle fibers to neuromuscular junctions, and understand how they support movement, muscle tone, and other bodily functions.

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Understanding the Muscular System: Structure and Function

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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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