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The Muscular System

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  1. The Muscular System Chapter 6

  2. Skeletal Muscle • Bundles of striped muscle cells • Attaches to bone • Often works in opposition biceps triceps

  3. Tendons Attach Muscle to Bone muscle tendon bursae synovial cavity

  4. TRICEPS BRACHII Human Skeletal Muscles BICEPS BRACHII PECTORALIS MAJOR DELTOID TRAPEZIUS SERRATUS ANTERIOR EXTERNAL OBLIQUE LATISSIMUS DORSI RECTUS ABDOMINUS GLUTEUS MAXIMUS ADDUCTOR LONGUS BICEPS FEMORIS SARTORIUS QUADRICEPS FEMORIS GASTROCNEMIUS TIBIALIS ANTERIOR

  5. Skeletal Muscle Structure • A muscle is made up of muscle cells • A muscle fiber is a single muscle cell • Each fiber contains many myofibrils myofibril

  6. Sarcomere A myofibril is made up of thick and thin filaments arranged in sarcomeres sarcomere sarcomere sarcomere sarcomere Z band Z band Z band

  7. Muscle Microfilaments Thin filaments • Like two strands of pearls twisted together • Pearls are actin • Other proteins in grooves in filament Thick filaments • Composed of myosin • Each myosin molecule has tail and a double head

  8. Sliding-Filament Model • Myosin heads attach to actin filaments • Myosin heads tilt toward the sarcomere center, pulling actin with them

  9. Sliding-Filament Model Sarcomere shortens because the actin filaments are pulled inward, toward the sarcomere center

  10. Contraction Requires Energy • Muscle cells require huge amounts of ATP energy to power contraction • The cells have only a very small store of ATP • Three pathways supply ATP to power muscle contraction

  11. ATP for Contraction ADP + Pi Pathway 1 DEPHOSPHORYLATION CREATINE PHOSPHATE Relaxation Contraction creatine Pathway 2 AEROBIC RESPIRATION Pathway 3 GLYCOLYSIS ALONE glucose from bloodstream and from glycogen break down in cells oxygen

  12. Nervous System Controls Contraction • Signals from nervous system travel along spinal cord, down a motor neuron • Endings of motor neuron synapse on a muscle cell at a neuromuscular junction

  13. Role of Calcium in Contraction • T tubules in the sarcoplasmic reticulum relay signal • Calcium ions are released

  14. Troponin and Tropomyosin • Lie in groove in actin filament • When muscle is relaxed, tropomyosin blocks myosin binding site • When troponin binds calcium ions, it changes shape and moves tropomyosin • Cross-bridge formation and contraction can now proceed

  15. Muscle Tension • Is mechanical force a contracting muscle exerts on an object • For a muscle to shorten, muscle tension must exceed the load that opposes it • The load may be the weight of an object or gravity’s pull on the muscle

  16. Two Main Types of Contraction • Isotonic contraction • Muscle visibly shortens; moves a load • Tension remains constant as the muscle changes length • Isometric contraction • Muscle does not change length • Tension is insufficient to move load

  17. Motor Unit • One neuron and all the muscle cells that form junctions with its endings • When a motor neuron is stimulated, all the muscle cells it supplies are activated to contract simultaneously • Each muscle consists of many motor units

  18. peak relaxation Twitches and Tetanus stimulus contraction starts time number of stimuli per second number of stimuli per second tetanic contraction twitch repeated stimulation

  19. Two Types of Skeletal Muscle • Slow, or red, muscle • Many capillaries, high myoglobin • Contracts fairly slowly • Can sustain contraction • Fast, or white, muscle • Fewer capillaries, less myoglobin • Contracts quickly • Cannot sustain contraction

  20. Muscle Fatigue • An inability to maintain muscle tension • Occurs after a period of tetanic contraction • Different types of muscle show different fatigue patterns