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