How do muscles contracts?

Answer 1

Muscles are mainly composed of alternating rows of myosine protein filaments and actin protein filaments. When the muscle is relaxed those rows are least overlapped. When the nervous impulse commands the muscle to contract these rows overlap making the muscle shorter in length and causing a mechanical function.

The muscle contraction process first happens by a motor neuron being activated. This produces an action potential that passes outward in a ventral root of the spinal cord where it is conveyed to a motor end plate on each muscle fiber. The action potential causes the release of packets of acetylcholine into the synaptic clefts on the surface of the muscle fiber. The acetylcholine causes the electrical resting potential under the motor end plate to change, and this then initiates an action potential which passes in both directions along the surface of the muscle fiber. At the opening of each transverse tubule onto the muscle fiber surface, the action potential spreads inside the muscle fiber. At each point where a transverse tubule touches part of the sarcoplasmic reticulum, it causes the sarcoplasmic reticulum to release Ca+2 ions. The calcium ions result in movement of troponin and tropomyosin on their thin filaments, and this enables the myosin molecule heads to "grab and swivel" their way along the thin filament. This is the driving force of muscle contraction.

in order for a muscle fiber to contract there are several steps before getting a response. (obviously they happen at an unbelievable 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 synaps, and Acetylcholine (ACh) is released into the synaps, and goes onto the sarcolema (but never touches) and binds to the ACh receptor cites, then the sarcoplasmic reticulum realeases calcium, and the calcium binds to troponin (top of actin) and troponin begins to change shape and tropomyosin slides off of the active cites and the cites 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.

Read more: [[Q/How does muscle contract#ixzz161moMP5D|How_does_muscle_contract]]

Answer 2

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