1. ANATOMY Unit 3 Notes: Sliding Filament Theory

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 to Muscle Cause:
Conscious decision to move
Homeostatic response
Nervous System Sends a Message to the Effector Organ:
Neurotransmitter released (ACh, acetylcholine)
ACh binds to sarcolemma of muscle fiber
ACh initiates opening of sodium-potassium channels

4. (3) Depolarization of the Muscle
Cause:
Binding of ACh to sodium-potassium channels
Opening of channels + Movement of Na-K+ across sarcolemma
Involves the Movement of Charges:
More Na+ moves in, Than K+ moves out
Imbalance of charges  electrical current (action potential)

5. (4) The Release of Calcium
Cause: Depolarization
Action Potential across the Sarcoplasmic Reticulum causes the release of Calcium:
Ca+ released from membrane of sarcoplasmic reticulum.
Ca+ binds with troponin:
Troponin-Tropomyosion conformation changes
Troponin & Tropomyosin no longer cover Actin
Actin is exposed

6. (5) Myosin interacts with 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
(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