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Muscle Contraction and Relaxation

Muscle Contraction and Relaxation. Important Muscle Fibres:. Thin Filaments – Actin Thick Filaments - Myosin. Contraction:. Myosin grabs onto the actin filaments Forms “CROSSBRIDGES ” ATP (energy) and Ca ++ ions are needed for contraction. Actin Fibre. Myosin Fibre. Relaxation:.

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Muscle Contraction and Relaxation

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  1. Muscle Contraction and Relaxation

  2. Important Muscle Fibres: • Thin Filaments – Actin • Thick Filaments - Myosin

  3. Contraction: • Myosin grabs onto the actin filaments • Forms “CROSSBRIDGES” • ATP (energy) and Ca++ ions are needed for contraction Actin Fibre Myosin Fibre

  4. Relaxation: • ATP now pumps Ca++ out of muscle cell • Myosin releases actin filaments

  5. Sliding Filament Theory • https://www.youtube.com/watch?v=0kFmbrRJq4w

  6. Forensics Again!

  7. Rigor Mortis (stiffness of death) • ATP has been used to contract the muscles • Actin and myosin remained linked = WHY? • Relax when the muscles start to decompose

  8. Order of Rigor Facial muscles, eyelids, neck and jaw Trunk and internal organs Extremities (Disappears in the same order from head down) *also starts first in muscles that were exercising

  9. Cadaveric Spasm

  10. Timeline of Rigor • Becomes apparent at 2-4 hours after death. • Complete at 12-18 hours after death. • Begins to go away 18-36 hours after death. • Usually disappeared 48-60 hours after death.

  11. Algor Mortis (coldness of death) • Reduction of body temperature after death • Temperature taken under armpit, in the ear or rectally (most accurate) • First 12 hours bodies lose 1.4⁰C per hour • After 12 hours bodies lose 0.7⁰C per hour • General Formula: • hours dead = (37 ⁰ C – body temp)/1.4 ⁰C • Affected by clothing, body fat, illness, age, etc.

  12. Pallor Mortis (paleness of death) • Occurs 15 – 30 minutes after death • Blood sinks to lower parts of the body • Not much use to determine time of death

  13. Livor Mortis (blueness of death) • AKA Lividity • Blood settles in the body at the lowest point • Doesn’t settle in spots with pressure

  14. Timeline of Livor Mortis • Starts 20 min – 3 hr after death • Maximizes at 6 – 12 hours • Blood is congealed after 12 hours • Can help determine if body has been moved • Can help determine time of death • Press skin – pale – colour returns < 12 h

  15. Other Ways to Estimate Time of Death: • Stomach Contents – calculate the degree of digestion of food • Insect activity – observe lifecycle of flies (including eggs and larvae)

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