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The Muscular System

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  1. The Muscular System

  2. Objective: • The student will become familiar with the structure and function of the muscular system

  3. Question of the day: What moves you?

  4. Composition: • The musclar system makes up 40-50% of total body weight • The muscular system is • 75% water • 20% proteins • Actin and Myosin • 5% miscellaneous carbohydrates, fats, and inorganic salts

  5. Terms to know: • Myology: study of muscle • Tendons connect bone to muscle • Fascia • Loose connective tissue • Aponeurosis • Sheet of connective tissue that connects muscle to muscle

  6. Function: • The primary function of muscle is to …. PULL • Muscles work in opposing pairs • While one pulls, the other relaxes

  7. Types of muscle tissue:

  8. Voluntary (skeletal) muscle function: • Movement • Physical movement of the body • Posture • Maintain body position • Heat production • Muscles give of 65% of their energy production as heat • Works to maintain a constant body temperature

  9. Smooth (involuntary) Muscle function: • Movement of substances through body tubes • Ex. Peristalsis in the esophagus • Expulsion of stored substances • Ex. Gallbladder • Regulation of the size of openings • Ex. Iris of the eye • Regulation of the diameter of tubes • Ex. Blood vessels

  10. Characteristics of Muscle Tissue: • Excitability (irritability) • Abilitiy of muscle to be stimulated to evoke response • Contractility • Function of muscle as a contractile unit • Muscle’s ability to contract/shorten • Extensibility • The ability of a muscle to stretch

  11. Characteristics of Muscle Tissue: (cont.) • Elasticity • The ability of the muscles to return to normal shape after being stretched or muscle contraction • Conductivity • The ability to conduct an electric impulse along the entire length of the muscle

  12. Fascia: • Loose connective tissue that “wraps” muscle tissue • Superficial fascia: subcutaneous layer that holds skin to muscles • Deep fascia: more fibrous than superficial hold muscles together

  13. Functions of Fascia: • Storehouse for water • Insulation • Mechanical protection • Houses blood vessels and nerves

  14. Muscle Structure

  15. Epimyseum: tissue that wraps the entire muscle (found deep to the fascia) • Perimyseum: smaller units of muscle • Holds the fascicles together • Fascicle: collections of the smaller unit • Group of individually wrapped fibers • Endomysium: wrapping of the smaller unit • Each muscle fiber (myofiber) is surrounded by a plasma membrane individually wrapped in a sheet of endomysium

  16. Sarcolemma is comparable to the plasma membrane of a muscle fiber • Sarcoplasm • Liquid environment within a muscle cell that contains calcium ions surrounding the myofibrils • Myofibrils are made up of 2 types of filaments (myofilaments) • Actin and Myosin • Adjacent myofilmaments line up with each other so that the Z-line of one sarcomere lines up with the Z-line of an adjacent myofibrils • T-tubules • Are extensions of the sarcoplasmic reticulum that run transversely along muscle fibers • Hold substances needed for muscle contraction


  18. The contractile unit of muscle:

  19. Think about it … • Tendons are continuous with the epimysium surrounding the larger muscle • Tendons connect muscle to bone

  20. Why do we have all of this? • All of these components are necessary to create movement • Muscle generates movement • Muscle is living tissue • Requires blood supply and nerve innervation

  21. How do muscles create movement? • Well actually they don’t … the Brain does.

  22. Movement: • Movement is initiated in the brain which is part of the Central Nervous System (CNS) with the initiation of an action potential • The impulse travels down the spinal cord out to the motor neuron which carries the electrical impulse to the muscle • Between the motor neuron and muscle is a synapse

  23. What is needed to create movement? • Mitochondria • Power house of the cell • Produce energy in the form of ATP with the help of myoglobin • T-tubules • extension of the sarcoplasmic reticulum • Hold substances needed for muscle contraction

  24. Myofilaments • Actin and myosin • Myosin has a hook-like binding site while actin has a bulb shaped binding site • These binding sites are not readily available • The binding sites on actin and myosin are covered by tropomyosin and troponin • This is to keep the binding sites from attaching to one another during a relaxed state

  25. Sliding Filament Mechanism: • Brain says move • Impulse travels down spinal cord • Impulse travels out spinal nerve to periphery (the muscle you want to move) • The impulse travels down the motor neuron • The impulse reaches the presynaptic bulb of the motor neuron where (ACh is stored in vesicles, the sarcolemma is semipermeable and polarized due to Na+ and K+ ions gathering outside the sarcollema)

  26. The impulse crosses the neuromuscular junction (NMJ) with the help of ACh • The junction of the motor neuron and muscle fiber • As soon as the ACh hits the sarcolemma the action potential is stimulated and the permeability of the sarcolemma is changed or depolarized. • The wave of depolarization continues down the length of the muscle fiber.

  27. Wave of depolarization releases Ca+ ions from the sarcoplasmic reticulum • Actin and myosin have on their surface binding sites so that the myofibrils can bind together to create muscle contraction • Binding sites are protected by Troponin/Tropomyosin to prevent the myofibrils from binding to each other when the muscle is at rest • Ca+ ions push Troponin/Tropomyosin away from the binding sites on actin and myosin, making the binding sites readily available for the creation of cross-bridges

  28. ATP (created by the mitochondria by/with myoglobin) allows for a power stroke • Pushes the Z-lines of the sarcomere closer together • AChE (Acetylcholine Esterase) is secreted which destroys ACh which allows the sarcolemma to go back to its resting state (repolarized)

  29. What can interfere with muscle contraction? • Oxygen debt: can’t get enough oxygen into the body so we start to build up lactic acid • Lactic acid is “poison” to the muscles • Slows the reclaiming of Ca+ ions so the muscles won’t fully relax • Muscle Fatigue: is largely the result of the depletion of oxygen and/or glycogen

  30. Rigor Mortis • “when muscles tighten after you die” • When a person dies they no longer posses oxygen so lactic acid builds up and the sarcoplasmic reticulum breaks down releasing Ca+ ions and the muscles contract • Rigor can last for 12-20 hours

  31. 3 Major Energy systems for Muscle contraction: (Anaerobic processes) • Available ATP • Phosphagen system • Glycolysis

  32. Available ATP: • Immediate energy source • Good for the first 5-6 seconds of energy expenditure

  33. Phosphagen system: • Contained in muscles • High energy molecule creatine-phosphate or phospho-creatine • Capable of delivering lots of energy in a short period of time • 15 second energy bursts

  34. Glycolysis: • “glucose splitting” • Breakdown of carbohydrates (glucose = C6H12O6) • The Liver: • Stores glucose in the blood • Converts stored energy into usable energy

  35. Muscles contract to create movement: • The All-or-none principle states that when a stimulus is applied a muscle fiber will contract completely or not at all • No such thing as a partial contraction • Strength of contraction depends on the number of fibers stimulated

  36. How do muscles contact? • EMG (electromyogram) find diseases that damage muscle tissue, nerves, or the neuromuscular junctions (nmj)

  37. EMG output (myogram):

  38. Types of muscle contraction: • Tetanous: continuous contraction/continuous stimulation • Voluntary movement • Single contraction: twitch • Wave summation: staircasing effect

  39. Types of muscle contraction (cont.) • Isotonic: “iso” = same • “tonic” = force • Contraction that remains at the same force throughout • Isometric: “iso” = same • “metric” = length • Contraction, no movement

  40. Types of muscle contraction (cont.): • Concentric: muscles shorten while generating force • “positive” lift • Eccentric: the muscle elongates while under tension due to an opposing force being greater than the force generated by the muscle. • “negative” lift • Rather than working to pull a joint in the direction of the muscle contraction, the muscle acts to decelerate the joint at the end of a movement or otherwise control the repositioning of a load.

  41. Movement: • Most muscles cross at least one joint • Some cross 2 or even 3 joints • When muscles contract they pull with equal force from both ends • One end of the muscle must be stable to create movement

  42. Terminology: • Origin: immovable end of the muscle • Where the muscle “starts” • Insertion: moveable end of the muscle • The end of the muscle that the force is applied to • Belly: “meaty” part of the muscle • Where the actual muscle contraction occurs

  43. Levers: • The body moves through a system of levers • Muscle pull works around these levers • Levers also give the body a mechanical advantage • This means that it takes less force to create movement therefore making the muscles job “easier”

  44. Classes of levers:

  45. Group Actions: • Agonist • “prime mover” • The muscle that initiates the movement • Synergist • Muscles that work together to generate movement • Antagonist • Muscles that work against the prime movers • Fixators/Stabilizers • Muscles that stabilize a joint or bone so that another muscle can work more efficiently

  46. How are muscles named? • 600-700 muscles in the body • Direction of fibers • Location • Size of the muscle • Number of heads of origin • Shape • Origins and insertions • Action

  47. Terminology: • Hypertrophy: muscle growth (size) • Atrophy: muscle shrinking • Myopathy: muscle disease • Myoma: muscle tumor • Myolatia: muscle softening • Myocitis: inflammation of muscle tissue