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Muscular System

Muscular System. Muscle Tissue and Organization. Muscle Tissue. Muscle tissue is one of the 4 primary tissue types Three types of muscle tissue Skeletal – moves the body Cardiac – heart muscle Smooth – moves fluid and solids through the digestive tract. Characteristics of Muscle Types.

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Muscular System

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  1. Muscular System Muscle Tissue and Organization

  2. Muscle Tissue • Muscle tissue is one of the 4 primary tissue types • Three types of muscle tissue • Skeletal – moves the body • Cardiac – heart muscle • Smooth – moves fluid and solids through the digestive tract

  3. Characteristics of Muscle Types • SKELETAL • Voluntary • Striated • Multinucleate • CARDIAC • Involuntary • Striated • Single nuclei • Intercalated discs • SMOOTH • Involuntary • Not striated • Single nucleus

  4. Features of Muscle Tissue • Contractility – ability to shorten and pull • Excitability – responds to stimuli • Elasticity – muscle can rebound to its original shape after contraction • Extensibility – ability to contract over a range of resting lengths

  5. Functions of Skeletal Muscle • Movement • Posture • Stabilize joints • Support soft tissue • Generation of heat • Regulate entrances and exits (orifices)

  6. Muscle Attachment • TENDONS attach muscle to bone • Dense regular CT • Each muscle has an ORIGIN and INSERTION, and a specific ACTION • The origin remains stationary while the insertion moves

  7. Connective Tissue of Muscle • Skeletal muscle has three layers of connective tissue • 1. EPIMYSIUM – dense irregular CT that surrounds the entire muscle • 2. PERIMYSIUM – divides muscle into compartments or bundles of muscle fibers called FASCICLES • 3. ENDOMYSIUM – surrounds each muscle fiber (muscle cell)

  8. Muscle Cell Terminology • Muscle cells are very long; muscle fibers • SARCOLEMMA – cell membrane • SARCOPLASM – cytoplasm • Sarcoplasm is filled with thousands of MYOFIBRILS that are responsible for contraction • Myofibrils are composed of MYOFILAMENTS • Myofilaments are composed of the proteins ACTIN and MYOSIN

  9. Sarcomere • Organization of thick(myosin) and thin filaments(actin) in the myofibrils • Movements of these filaments causes muscle contraction • Sliding filament theory • 1954 Sir Andrew Huxley and Rolf Niedeigerke • Myosin heads bind to the actin and pull or “slide” the actin past the myosin to shorten the sarcomere

  10. Sarcomere • Z line = end of sarcomere • I band = thin (actin) filaments • H zone = thick (myosin) filaments • A band = zone of overlap, thick and thin

  11. Thin Filaments • Twisted strands of globular G actin molecules • Each molecule of G actin has an active site that can bind to a myosin molecule • Thin filaments also have two other proteins associated it • Tropomyosin – covers active sites on actin • Troponin - holds tropomyosin in place

  12. Thick filaments • Bundles of myosin molecules • About 500 myosin molecules per bundle • Myosin molecules have heads that can cross bridge to actin active sites • The binding of myosin heads to actin result in muscle contraction

  13. Figure 9.4b Sarcomere Structure

  14. Muscle contraction-Sliding filament theory • Contraction exerts a pull – tension • Interaction between actin and myosin triggered by calcium ions and presence of ATP • Sliding filament theory: • H band and I band get smaller • Zone of overlap gets larger • Z lines move closer together • Width of A band remains constant

  15. Sliding Filament Theory • Myosin heads cross bridge to the actin active sites • Myosin attachment “pulls” the actin toward the center of the sarcomere • Contraction begins with release of Ca2+ from the terminal cisternae of the sarcoplasmic reticulum • The release of ions is the result of electrical stimulation of the muscle fiber

  16. Terminal cisternae and T tubules

  17. T-tubules • The t-tubules distribute the electrical signal for contraction deep into the muscle fiber • As the signal travels the terminal cisternae release calcium ions • Release of calcium cause the troponin molecule to change shape • Change in troponin causes a change in the position of tropomyosin, myosin can bind to action and contraction occurs!

  18. Nervous System Control of Contraction • Skeletal muscle fibers are controlled by a motor neuron • Place where the nerve fiber and muscle meet is called the neuromuscular junction • Synaptic terminal – end of axon • Acetylcholine – neurotransmitter • Motor unit – all the muscle fiber controlled by a single motor neuron

  19. Neuromuscular Junction

  20. Neuromuscular junction

  21. Muscle contraction

  22. Muscle relaxation

  23. Sarcomere contraction

  24. Sliding filaments

  25. Sliding filaments Sarcomere shortens, fiber contracts

  26. Other components of the sarcomere • Sarcoplasmic reticulum – stores Ca+² ions for muscle contraction • Transverse tubules – carry impulse to stimulate and coordinate contraction

  27. Sarcoplasmic reticulum

  28. Types of Skeletal Muscle Fibers • Fast fibers • Short duration, rapid fatigue • Anaerobic metabolism • Few mitochondria • Brief periods of intense exercise • Slow fibers • Longer duration • Aerobic metabolism • Myoglobin present for oxygen binding • Marathon running • Intermediate fibers • Greater resistance to fatigue • Similar to fast fibers but with more mitochondria

  29. Organization of Muscle Fibers • Parallel • Convergent • Unipennate • Bipennate • Multipennate • Circular

  30. Muscles and Leverage • Muscles “work” by leverage, moving at a joint • In the body the bone is the lever, the joint is the fulcrum • Three types of levers in the body • First-class • Second-class • Third-class (most common)

  31. Muscle Actions • Prime movers • Muscle mainly responsible for producing a certain action • Biceps brachii is prime mover for elbow flexion • Synergist • Assists the prime mover • Antagonists • Action opposite of prime mover • Triceps brachii is antagonist of biceps brachii

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