Essay On Muscle Contraction

Almost half of a human 's body weight is composed of muscle. There are three distinct types of muscle tissue: cardiac muscle, skeletal muscle, and smooth muscle. Each of the muscle tissues have different structures, properties, characteristics, and roles in our body. Properties of muscle tissues include excitability, contractility, extensibility, and elasticity. Contractility is the ability to shorten, which causes movement of the structures to which the muscles are attached. Excitability is the ability to respond or contract in response to chemical and/or electrical signals. Extensibility is the capacity to stretch to the normal resting length after contracting. Elasticity is the ability to return to the original resting length after a muscle

There are four steps in the muscle contraction cycle. At the beginning of contraction, the sarcoplasmic reticulum releases ca2+ into the sarcoplasm where they will bind to troponin.Troponin then moves tropomyosin away from the myosin binding sites on actin. Once binding sites are free the contraction cycle will begin. Step one of the contraction cycle is ATP Hydrolysis. During ATP hydrolysis the enzyme ATPase uses water to cleave a phosphate from ATP producing ADP and a free phosphate which remains attached to the myosin head. The energy that was released from breaking the chemical bond is used to move the myosin head into position for attachment to the actin molecule. Step two of the contraction cycle is Cross-Bridge formation. During cross bridge formation the myosin head attaches to the revealed myosin-binding site on actin forming a cross bridge between the two protein molecules. Step three of the contraction cycle is the power stroke. During stage three the release of ADP and P from the myosin head triggers the power stroke, the rocking of the myosin head pulls actin towards the M-line. The fourth stage of the contraction cycle is the detachment of myosin from actin.The end result is a shortening of the sarcomere,the distance between the Z discs shortens, the H zone disappears,the dark A band increases because the actin and the myosin overlap more, and the light I band