1. Notes: Sliding Filament Theory [Muscle Contraction Physiology]

2. (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)

3. (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

4. (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)

5. (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

6. (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!

7. (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

8. (7) Why is it called the Sliding Filament Theory? Movement of myofilaments causes contraction Myosin grabs actin & SLIDES them towards the center

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