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Skeletal Muscle Contraction

Skeletal Muscle Contraction. Adrian Lui Kinesiology – OTHS Mrs. Coe. About Me. OTHS Graduate University of Waterloo – Kinesiology (BSc.) Brock University – Muscle Physiology (MSc.) University of Canterbury – Secondary Education (Grad. Dip) Ask me anything!. In T wo Periods….

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Skeletal Muscle Contraction

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  1. Skeletal Muscle Contraction Adrian Lui Kinesiology – OTHS Mrs. Coe

  2. About Me • OTHS Graduate • University of Waterloo – Kinesiology (BSc.) • Brock University – Muscle Physiology (MSc.) • University of Canterbury – Secondary Education (Grad. Dip) • Ask me anything!

  3. In Two Periods… • Motor Neurons • Passing the message from brain to muscle • Excitation Coupling • “Interpreting” the signal • Sliding Filament Theory • Physical contraction

  4. Muscle Anatomy

  5. Muscle Anatomy OUTSIDE Muscle Belly Epimyesium - The prefix means “outside” (epi) Fasciculus “Perimyesium” - The prefix means “around” (peri) Muscle Fibre “Epimyesium” - The prefix means “Inside” (endo) SARCOLEMMA

  6. The Motor Unit – Squeeze Game p. 35

  7. The Motor Unit • Sends from the neuron body to the muscle fibres • (AP) depolarizes (travels down) the axon hillock as it hops over the myelinated sheathes

  8. AP’s: All or None • Once an electrical signal fires, ALL muscle fibres associated with the motor neuron WILL contract • A single motor unit may stimulate anywhere between to muscle fibres

  9. Neuromuscular Junction • AP depolarizes to the axon terminal • The electrical signal causes a release of chemicals (neurotransmitters):

  10. Neuromuscular Junction • Acetylcholine (Ach) crosses the and attaches to the Ach receptors on the motor end plate of the muscle fibre • This in turn sends another electrical signal within the muscle fibre

  11. T - Tubules • The electrical signal from the motor end plate travels to the T-Tubules and causes a physical reaction at the

  12. Down the T-Tubules • AP causes the release of calcium from the __________________ (SR) • Calcium (Ca2+) travels from an area of high concentration to low concentration • Ca2+ the major signaling messenger for muscle contraction

  13. Review • Message sent from brain (CNS) to spinal cord and then to the limb (PNS). • Message (action potential) travels from the cell body of a neuron, down its axon to the axon terminal. • Acetylcholine (Ach) is released from the axon terminal where it binds to receptors found on the motor end plate of the muscle fibre. • The receptors initiate another action potential down the T-Tubules and causes the release of calcium from the sarcoplasmic reticulum.

  14. Ca2+ is release …

  15. Ca2+ interacts with Myofibrils (Myosin & Actin)

  16. Sliding Filament Theory

  17. Sliding Filament Theory • Originally, it was thought that myosin would curl up in and physically shorten when muscle is contracted • This was disproved when the width of the A Band (myosin) ___________ change during contraction • It was discovered that Myosin and Actin ___________ over each other during contraction

  18. Myosin • Also known as: _________ • Golf Clubs (Drivers) bundled together with heads facing outward • Has a binding site for: _________ • Does most of the work in the “power stroke”

  19. Actin • Also known as: __________ • Globules arrange like a winding chain • Is associated with Troponin and Tropomyosin • Is the ______________ for the power stroke

  20. ATP Binds… • ATP binds to myosin head • Myosin binds to actin in a “_________” position

  21. ATP = ADP + Pi • ATP is broken down and _________ is released causing a _________________ where myosin slides past actin • ADP and Pi are released from the myosin head

  22. Another ATP binds … • A fresh ATP binds as the myosin dissociates (weakly binds) with Actin • It’s ready to go again!

  23. But where does Ca2+ come in?

  24. Troponin and Tropomysoin • _____________ Ca2+ bound to troponin, Tropomyosin BLOCKS myosin from binding onto actin • Therefore, Ca2+ needs to be present and binds to troponin

  25. Troponin and Tropomysoin • With Ca2+ bound to ___________ , _____________ slides out of the way to allow actin / myosin interaction

  26. How do stop Contraction? • Sarcoplasmic (endo) Recticulum Calcium ATPase (SERCA) • SERCA pumps Ca2+ back into the SR against a concentration gradient • Therefore requires energy

  27. Concentric vs Eccentric • Concentric = shortening WHILE creating force • Eccentric = lengthening WHILE creating force How do we create force then? • The ____________ of actin / myosin interactions (or crossbridges formed)

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