I have just bumped into this great animated infographic which teaches how skeletal muscles function. I think, in order to get results we want from bodybuilding and working out; it is important understand how our body works. Of course, not all the aspects of it, but general knowledge is always useful.
The difference between them is that skeletal muscles are controlled by us while the other two are not. Skeletal ones need the input from neurons to function.
I do not want to go deep into this topic since all the necessary information is included within this infographic. However, I have added some of my ideas to understand the whole thing easier, and I include some links that are related to this topic. These are mainly Wikipedia pages where you can learn more about these things.
Skeletal muscle structure and function / Credit: imgur.com/fgRP0H7
As you see, the trigger is at the neuron synapse. The electrical impulses that are carried along the neurons are responsible for the moves. ACh, a neurotransmitter allows the neurons to signal the muscle cells.
The T-tubules is responsible for propagating the signal in the whole muscle cell. A special calcium ion is used in order to signal the molecules.
Here is a video that may help you to understand the whole process easier. To tell the truth, for me it was a bit hard to understand first, and this video helped a lot.
That is all I hope you now understand who your muscles function. If you have any questions or other sources that should be mentioned here, please take some time to share with us.