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Human Biology, Bios 103 Dr. Harry Schutte

Human Biology, Bios 103 Dr. Harry Schutte. CHAPTER 6 The Muscular System. The Muscular System. Figure 6.2 Slide 6.1. Principle function Contraction: shorten distance between bones Skeletal muscle moves bone Muscle groups

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Human Biology, Bios 103 Dr. Harry Schutte

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  1. Human Biology, Bios 103 Dr. Harry Schutte CHAPTER 6The Muscular System

  2. The Muscular System Figure 6.2 Slide 6.1

  3. Principle function Contraction: shorten distance between bones Skeletal muscle moves bone Muscle groups Synergistic: groups work together (hamstring group contracts together to extend lower leg) Antagonistic: groups oppose each other (biceps and triceps, ex.) Muscle Function:Produce Movement or Generate Tension Slide 6.2

  4. Fascicles: bundles, CT(connective tissue) covering on each one Muscle fibers: muscle cells Muscle Structure Figure 6.3 Slide 6.3

  5. Sarcomere: individual contractile units of the muscle (from one Z Line to the next Z Line) May be 100,000 sarcomeres in one myofibril arranged end-to-end. Myofibrils: bundles of contractile tube-like structures that make up the muscle cell Actin and myosin: the proteins of muscle contraction in the myofibrils Z Lines: attachment points for sarcomeres Skeletal Muscle Contractile Unit Slide 6.4A

  6. Skeletal Muscle Contractile Unit (cont.) Figure 6.5 Slide 6.4B

  7. Acetylcholine released from motor neuron at neuromuscular junction. This same neurotransmitter used at ALL nerve- skeletal muscle junctions in the body. KNOW THIS. Electrical impulse transmitted along T tubules Calcium released from sarcoplasmic reticulum Nerve Activation of Individual Muscle Cells Slide 6.5A

  8. Nerve Activation of Individual Muscle Cells (cont.) Figure 6.6 Slide 6.5B

  9. Thick filaments: myosin – studded with cross bridge “heads” Thin filaments: strands of actin molecules – slide between the myosin filaments Contraction = formation of cross bridges between thin and thick filaments (“sliding filament” mechanism) Calcium Initiates the Sliding Filament Mechanism Slide 6.6A

  10. Calcium Initiates the Sliding Filament Mechanism (cont.) Figure 6.7 Slide 6.6B

  11. Calcium released from sarcoplasmic reticulum Calcium binds to troponin Troponin-tropomysin complex shifts position Myosin binding site exposed Myosin heads form cross-bridges with actin Actin filaments pulled toward center of sarcomere Without calcium – no muscle contraction; too much calcium – muscles in spasm (can’t relax) Mechanism of Muscle Contraction Slide 6.7A

  12. Mechanism of Muscle Contraction (cont.) Figure 6.8 Slide 6.7B

  13. Nerve activation ends, contraction ends Calcium pumped back into sarcoplasmic reticulum Calcium removed from troponin Myosin-binding site covered No calcium = no cross-bridges Too much calcium (or not removed) = spasm Muscle Relaxation Slide 6.8

  14. Principle source of energy: ATP ATP needed to 1) “cock” the myosin heads in the “ready to fire” position 2) allows the cross-bridge to disengage After death, the lack of ATP keeps cross-bridges engaged: this is the cause of rigor mortis (KNOW THIS) ATP replenished by variety of means Creatine phosphate (assists in the bonding of P to ADP) Creatine supplements are not needed or used by the body, all you are doing is making “expensive urine” – the body makes plenty of creatine, it is not stored when a supplement is taken [the textbook is WRONG on this point – page 133] Stored glycogen used for initial 3-5 minutes of exercise Aerobic catabolism of glucose, fatty acids, and other high-energy molecules for long term energy and exercise Energy Required for Muscle Activity Slide 6.9

  15. Isotonic contractions: muscle shortens, movement occurs Isometric contractions: muscle doesn’t shorten, no movement Degree of nerve activation influences force Motor unit: a nerve and all of the muscle cells it innervates Muscle tension: the mechanical force generated by muscles when they contract All-or-none principle: muscle cells never contract on their own and a contraction is never partial – the myofibril bundles ALL contract and ALL perform a complete contraction Twitch: complete cycle of contraction and relaxation Muscle tone: some motor units are contracting and some relaxing at any one time in a whole muscle – creates an intermediate level of “background” force in the muscle Recruitment: increasing tone (or force of contraction) by activating more motor units Activity of Muscles Can Vary Slide 6.10

  16. Latent period: from stimulation to contraction starts Contraction: time during which muscle shortens Relaxation: muscle returns to its original length Muscle Contraction: Myogram Summation: increasing muscle force by increasing rate of motor unit stimulation Tetanus: stimulation rate so frequent that muscle cannot relax and stays in continuous maximum contraction (spasm) Figure 6.10 Slide 6.11

  17. Slow twitch vs. fast twitch fibers Slow twitch: endurance, long duration contraction, contain myoglobin (thigh muscles of a marathon runner, ex.) Jogging, swimming, biking Fast twitch: strength, white muscle, short duration contraction (forearms of baseball slugger, ex.) Sprinting, weight lifting, tennis Muscle Activity Slide 6.12

  18. Strength training Resistance training Short, intense Builds more fast-twitch myofibrils Aerobic training Builds endurance Increases blood supply to muscle cells Target heart rate (65-85% of [220 – your age]) at least 20 minutes, three times a week Exercise Training Slide 6.13

  19. Activation of cardiac and smooth muscles Involuntary Specialized adaptations in each Speed and sustainability of contractions Arrangement of myosin and actin filaments Regular arrangement in cardiac Attachments at various angles in smooth muscle, not regular Features of Cardiac and Smooth Muscles Slide 6.14

  20. Muscular dystrophy: genetic disorders that lack a particular muscle protein (dystrophin), loss of muscle fibers, muscle wasting and weakness Tetanus: “lock jaw”, a common problem before vaccinations, now is very rare, caused by bacteria toxin that over stimulates motor unit nerves Muscle cramps: “charley horse” uncontrolled muscle contractions due to ATP, potassium, muscle fatigue, dehydration or build-up of lactic acid Pulled muscles: a “strain”, muscle fibers are torn with bleeding, swelling, pain Plantar Fasciitis: inflammation of the broad ligament in sole of foot, very painful, treated with steroid injections Diseases and Disorders of the Muscular System Slide 6.15

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