16 Steps of Muscle Contraction

13th step

ATP is hydrolyzed to ADP and Pi ("recocking" the myosin head)

4th step

An action potential travels along membrane of the muscle cells and moves deep into the muscle cell by the T tubules

1st step

An impulse arrives at the synapse between the motor neuron (presynaptic terminal) and the muscle fiber (postsynaptic terminal)

7th step

Calcium ions bind to the troponin

6th step

Calcium ions diffuse into the sarcoplasm

16th step

Calcium ions return to the sarcoplasmic reticulum (returning the troponin-tropomyosin complex over the active sites on the G-actin) and the muscle relaxes

12th step

Cross bridges are released from the actin

9th step

Myosin cross bridges (that have hydrolyzed ATP prior to this event) bind to the actin

11th step

New ATP binds to the myosin head

3rd step

Permeability of the muscle plasma membrane is altered, sodium channels open, causing an action potential

14th step

Steps 9-13 continue

10th step

The power stroke occurs and ADP and Pi are released (mysosin and actin are still attached)

15th step

The sarcomere shortens

5th step

The sarcoplasmic reticulum becomes more permeable to calcium ions (calcium ions are released)

2nd step

The transmitter substance (usually acetylcholine in muscles) diffuses across synaptic cleft at the neuromuscular junction

8th step

The troponin-tropomyson complx moves away from the active sites on the G-actin