Nerve signals from the motor neuron arrive at synaptic knob of the motor neuron
The motor neuron’s voltage-gated calcium channels open and calcium rushes in
Calcium causes the motor neuron to release a neurotransmitter called acetylcholine
Acetylcholine travels across the gap that is between the motor neuron and the muscle fiber called the synaptic gap
Acetylcholine binds to the muscle fiber’s ligand-gated ion channels
Sodium rushes into the muscle fiber and potassium leaves the muscle fiber. This causes a voltage change inside the muscle fiber.
An action potential occurs and it travels down the muscle fiber causing calcium to be released from an organelle within the muscle fiber
Calcium binds to a thin filament/protein called troponin.
Troponin changes shape and causes a thin filament/protein called tropomyosin to shift position
This shift cause binding sites on a thin filament/protein called actin to be exposed
A thick filament/protein called myosin binds to actin’s exposed binding sites
Myosin performs a power stroke that pulls actin towards the center of myosin. In other words, the power stroke increases the degree to which myosin and actin overlap. This power stroke shortens the contractile unit of the myofibril called the sarcomere. ADP, phosphate, and energy are released during the power stroke.
ATP binds to myosin and this causes myosin to release actin.
The ATP molecule on myosin is hydrolyzed (broken down) into ADP, phosphate, and energy; however they are not released from myosin. As a result, myosin performs a recovery stroke.
Steps 11 through 14 repeat until calcium is pumped back into the muscle fiber’s organelle that released it
Source: Saladin, Kenneth S. Anatomy and Physiology : The Unity of Form and Function. 4th ed. New York: McGraw-Hill Education, 2006. 415-419.
