How does muscle contractions?

Answer 1

It would be impossible for you to do anything without your muscles. Absolutely everything that you conceive of with your brain is expressed as muscular motion. The only ways for you to express an idea are with the muscles of your larynx, mouth and tongue (spoken words), with the muscles of your fingers (written words or "talking with your hands") or with the skeletal muscles (body language, dancing, running, building or fighting, to name a few).

In order for a muscle fiber to contract there are several steps before getting a response. (obviously they happen at a high speed, so we don't notice it) but first the brain has to send a signal to the nerve, then an electrical impulse travels down the axon to the synapse, and acetylcholine (ACh) is released into the synapse, and goes onto the sarcolema and binds to the ACh receptor sites, then the sarcoplasmic reticulum releases calcium, and the calcium binds to troponin (top of actin) and troponin begins to change shape and tropomyosin slides off of the active sites and the sites then become available for myosin to bind on. Myosin then grabs onto actin and ratchets head to slide actin forward, myosin goes all the way down the line and ratchets all of actin until the muscle fiber is completely contracted.