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MUSCULAR SYSTEM

Explore the structure, functions, and characteristics of the muscular system. Learn about skeletal, cardiac, and smooth muscle tissues, as well as muscle fiber anatomy and neuromuscular junctions. Understand muscle contraction and energy metabolism in skeletal muscles.

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MUSCULAR SYSTEM

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  1. MUSCULAR SYSTEM

  2. I. Overview • Muscles – 40-50% of body mass • Functions • skeletal movement • control of organ and vessel size • maintain posture and position • support soft tissue • guard entrances and exits • maintain body temperature (85%)

  3. 3 Kinds of Muscle Tissue • Skeletal • Striated • Voluntary • AKA: Somatic Tissue

  4. C. 3 Kinds of Muscle Tissue 2. Cardiac • Heart muscle • Branched cells • Multinucleiated • Thick striations • Intercalated discs • Increase speed of impulses • Involuntary • AKA Visceral Tissue

  5. 3 Kinds of Muscle Tissue • Smooth • Spindle shaped • Nonstriated • Involuntary • Found around hollow organs such as arteries, esophagus, stomach

  6. D. Muscle Characteristics • Contractility Ability to shorten and exert tension • Excitability Ability to respond • Extensibility Ability to contract after being stretched • Elasticity Ability to regain initial length after contraction

  7. I. Overview E. Each muscle is an organ comprised of • Muscle tissue • Connective tissues • Nervous tissue • Blood

  8. II. Anatomy of Skeletal Muscle • Connective Tissue • Superficial Fascia Surround and separate each muscle

  9. A.Connective Tissue 2. Deep • Epimysium - whole muscle • Perimysium - bundles of fibers (fascicles) • Endomysium- single muscle fiber

  10. A.Connective Tissue 3. Tendons • Formed from the union of all three deep fascia • Connect muscle to bone

  11. A.Connective Tissue 4. Aponeurosis – flat sheet

  12. B. Muscle Fibers • Each muscle fiber • is a single, long, cylindrical muscle cell. • Sarcolemma (cell membrane) • Sarcoplasm (cytoplasm) • Many mitochondria • Nuclei • Sarcoplasmic reticulum

  13. B. Muscle Fibers 1. Each muscle fiber • is wrapped in endomysium

  14. 1. Each muscle fiber c. is a bundle of myofibrils which is made of a budle of myofilaments

  15. B. Muscle Fibers 2.Fascicles: • a bundle of muscle fibers • wrapped in perimysium

  16. B. Muscle Fibers 3. Myofibrils • made of thin and thick filaments

  17. B. Muscle Fibers 3. Myofibrils • Thick filaments made up of the protein myosin. c. Thin filaments are made up of the protein actin.

  18. Thick filaments

  19. Thin filaments Tropomyosin and troponin are regulatory proteins Actin and myosin are contractile proteins.

  20. B. Muscle Fibers 3. Myofibril d. Together, the thick and thin filaments make up the striations

  21. B. Muscle Fibers 4. Sarcomeres • Contractile unit of a muscle • Consists of overlapping thick and thin filaments Sarcomere

  22. B. Muscle Fibers 4. Sarcomere c. Muscle contraction • results from thick and thin filaments sliding past one another.

  23. C. Neuromuscular Junction 1. Where the neuron and muscle fiber meet • The neuron and muscle fibers it controls make up a motor unit (2-2000 fibers/unit)

  24. MOTOR UNIT

  25. C. Neuromuscular Junction 3.When stimulated, all of the muscle fibers of a motor unit contract all at once.

  26. C. Neuromuscular Junction 4. Anatomy Axon terminal – nerve end • Produces a neurotransmitter - acetycholine (Ach)

  27. C. Neuromuscular Junction 4. Anatomy Motor end plate – site on muscle with Motor end plate acetycholine receptors Synaptic cleft - space between the nerve & motor end plate

  28. III. Skeletal Muscle Contraction • nerve impulse • ACh released • Ach binds to receptor on muscle • Enzyme (Acetylcholine esterase removes ACh A. Initiation events

  29. III. Skeletal Muscle Contraction • ACh causes to Na+ to diffuse into cell • If threshold is reached, action potential occurs • - impulse travels along membrane resulting in contraction B. Action Potential

  30. III. Skeletal Muscle Contraction C. Sliding Filament Theory • Action potential causes Ca++ release from S.R • Ca++ binds to thin filament • Thin filament rotates exposing binding site for myosin • Myosin binds actin • uses ATP to "rachet" once • releases, "and binds to next actin

  31. Calcium is the "switch" that turns muscle "on and off" (contracting and relaxing).

  32. III. Skeletal Muscle Contraction D. How Neurotoxins Work • cobra toxin and curare • block Ach receptors • cause flaccid paralysis, potentially fatal respiratory arrest • nerve gas and insecticides • inhibit AchE • cause potentially fatal paralytic convulsions

  33. How a Nerve Gas Works Normal Nerve Gas

  34. Effect of Atropine on the Transmission of Acetylcholine in the presence of a nerve agent

  35. III. Skeletal Muscle Contraction D. How Neurotoxins Work • Botulism toxin and curare • block Ach release • cause flaccid paralysis, potentially fatal respiratory arrest • Tetanus toxin • cause excessive Ach release from motor neurons • causes potentially fatal paralytic convulsions (“lock jaw”)

  36. III. Skeletal Muscle Contraction E. Rigor Mortis • Ca++ pumps run out of ATP • Ca++ cannot be removed • continuous contraction • eventually tissues break down

  37. A. Aerobic Respiration IV. Energy Metabolism in Sk.Ms. • Most efficient use of glucose Sources of glucose include blood glucose and stored glycogen • 36ATP/glucose • requires oxygen • occurs in mitochondria • Muscle cells have more mitochondria than any other cell • Require a steady supply of O2

  38. B. Creatine-phosphagen system • During rest, muscles store energy as creatine phosphokinase (CPK or CK) • During intense exercise, ATP is depleted first, then CK is used to convert ADP back to ATP

  39. C. Lactic Acid Pathway • Anaerobic use of glucose • 2 ATP/ glucose • Lactic acid produced as waste product – Oxygen Debt • Is toxic to tissue • Can be recycled in liver

  40. V. Muscle Twitch-cycle of contraction and relaxation

  41. V. Muscle Twitch-cycle of contraction and relaxation A. Reasons for varying degrees 1. The number of muscle fibers innervated by a single neuron varies 2. Some motor units have lower thresholds than others 3. Muscle fibers differ functionally: fast twitch – slow twitch fibers

  42. V. Muscle Twitch B. Fast vs Slow Twitch Fibers 1. Differ in • How they make ATP • Speed of ATP break down • Mitochondria content • How fast they fatigue

  43. B. Fast vs Slow Twitch Fibers 2. Slow Twitch Fibers • Smallest fibers • Fatigue resistant • Aerobic ATP production • Many mitochondria • Slow contractions • Example: uroanal muscles

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