Which of the following is most accurate when discussing the sliding filament theory?
1. Nerve impulse (action potential) arrives at the neuromuscular
junction triggering the release of the neurotransmitter acetycholine
2. Sodium binds to the protein troponin which is located on the actin
myofilament
3. When energy (ATP) is released, troponin slides over actin and the
muscle shortens
4. Actin heads bend (cross bridge) to attached to the exposed binding
sites on the myosin myofilament