Notes: Sliding Filament Theory

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Notes Sliding Filament Theory

• Muscle Contraction Physiology

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(1) Muscle Contraction

• Sliding Filaments Muscle Contraction
• The Basic Steps
• 1- Message sent
• 2- Neurotransmitter
• 3- Depolarization
• 4- Calcium Troponin Actin Exposed
• 5- Actin Myosin (Contraction)

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(2) Neuron ? Muscle (Muscle Fiber)

• Cause
• Conscious decision to move
• Homeostatic response
• Nervous System ? Effector
• Neurotransmitter released (ACh, acetylcholine)
• ACh binds to sarcolemma of muscle fiber
• ACh initiates opening of sodium-potassium
  channels

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(3) Depolarization

• Cause
• Binding of ACh to sodium-potassium channels
• Opening of channels Movement of Na-K across
  sarcolemma
• Movement of Charges
• More Na moves in, Than K moves out
• Imbalance of charges ? electrical current (action
  potential)

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(4) Sarcoplasmic Reticulum ? Calcium

• Cause Depolarization
• Action Potential releases Calcium
• Ca released from membrane of sarcoplasmic
  reticulum to sarcomere
• Ca binds with troponin
• Troponin-Tropomyosion conformation changes
• Troponin Tropomyosin no longer cover Actin
• Actin is exposed

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(5) Myosin ? Actin

• Cause
• Troponin Tropomyosin unveils Actin
• Actin exposed
• Myosin releases Inorganic Phosphate ADP
• Pi ADP ATP
• Myosin changes conformation
• Myosin binds to Actin
• Myosin and Actin slide towards each other
• WE HAVE A CONTRACTION! WOO WOO!

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(6) Relaxation

• ATP binds back with myosin
• Myosin detaches and moves away from Actin
• Troponin Tropomyosin cover up Actin
• Ca moves back into Sarcoplasmic Reticulum
• Repolarization ? Sarcolemma stable again

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(7) Why is it called the Sliding Filament Theory?

• Movement of myofilaments causes contraction
• Myosin grabs actin SLIDES them towards the
  center

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(1-2) Depolarization of Sarcolemma Generation
of Action Potential
(3) Calcium Ions released from Sarcoplasmic
Reticulum
(10) Everything moves back contraction done!
(4-6) Calcium binds to troponin, tropomyosin
moves, actin exposed
(9) Calcium removed by active transport
(7-8) Myosin attaches to actin, Myosin moves
actin, ATP released