It is the activation of tension-generating sites within muscle fibers. In physiology, muscle contraction does not mean muscle shortening because muscle tension can be produced without changes in muscle length such as holding a heavy book or a dumbbell at the same position. Muscle contraction is the activation of tension-generating sites within muscle fibers. In physiology, muscle contraction does not mean muscle shortening because muscle tension can be produced without changes in muscle length such as holding a heavy book or a dumbbell at the same position.
Myosin is a motor protein that generates the force in a muscle contraction much like the stroke of an oar. It consists of a head and a tail region. Together, the tails of approximately three hundred myosin molecules form the shaft of the thick filament. In summary, myosin is a motor protein most notably involved in muscle contraction. Actin is a spherical protein that forms filaments, which are involved in muscle contraction and other important cellular processes. Tropomyosin is a long strand that loops around the actin chains in the thin filament. Troponin is a protein that helps hold tropomyosin in place on the actin filament. A muscle contraction consists of a series of repeated events. First, calcium triggers a change in the shape of troponin and reveals the myosin-binding sites of actin beneath tropomyosin Below are two different but similar descriptions of muscle contraction that explain the processes involved in notification, contraction, and relaxation. The following steps are involved in muscle contraction: (2) A motor neuron in the ventral horn of the spinal cord is activated, and an action potential passes outward in a ventral root of the spinal cord. (3) The axon branches to supply a number of muscle fibers called a motor unit, and the action potential is conveyed to a motor end plate on each muscle fiber. Muscle contraction is the activation of tension-generating sites within muscle fibers. In physiology, muscle contraction does not mean muscle shortening because muscle tension can be produced without changes in muscle length such as holding a heavy book or a dumbbell at the same position. The termination of muscle contraction is followed by muscle relaxation, which is a return of the muscle fibers to their low tension-generating state. Muscle contractions can be described based on two variables: length and tension. A muscle contraction is described as isometric if the muscle tension changes but the muscle length remains the same. In contrast, a muscle contraction is isotonic if muscle length changes but the muscle tension remains the same. Furthermore, if the muscle length shortens, the contraction is concentric to contraction in skeletal muscle. The trigger for a muscle contraction is an electrical impulse. The electrical signal sets off a series of events that lead to crossbridge cycling between myosin and actin, which generates force. The series of events is slightly different between skeletal, smooth and cardiac muscle.  (8) 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. (2) A motor neuron in the ventral horn of the spinal cord is activated, and an action potential passes outward in a ventral root of the spinal cord. (3) The axon branches to supply a number of muscle fibers called a motor unit, and the action potential is conveyed to a motor end plate on each muscle fiber. muscle contraction. the process of force-generation in the fibres of any class of muscle, by the interaction of myosin head-groups in the thick filaments with actin molecules in one of the immediately neighbouring thin filaments.  Through the process of muscle contraction, tension is developed within muscle tissue, which may or may not lead to movement of a part of the body. The term contraction often means to shorten; however, during a muscle contraction the tension may cause muscles to stay the same, get longer or become shorter. The physical process of the contraction happens quickly and in only a few steps. The two proteins that are responsible for muscle contractions are actin and myosin. When myosin and actin interact, it results in a change in the shape of the muscle cells. Contractions happen when actin filaments actually slide over myosin filaments. Contracting a Muscle. During contraction, the thin filaments slide past the thick filaments, shortening the sarcomere. The thick and thin filaments do the actual work of a muscle, and the way they do this is pretty cool. Thick filaments are made of a protein called myosin. At the molecular level, a thick filament is a shaft of myosin molecules arranged in a cylinder. Thin filaments are made of another protein called actin.
http://study.com/academy/lesson/muscle-contraction-actin-and-myocin-bonding.html http://meat.tamu.edu/ansc-307-honors/muscle-contraction/ https://en.wikipedia.org/wiki/Muscle_contraction http://health.howstuffworks.com/human-body/systems/musculoskeletal/muscle3.htm http://meat.tamu.edu/ansc-307-honors/muscle-contraction/ http://medical-dictionary.thefreedictionary.com/muscle+contraction http://www.wisegeekhealth.com/what-is-muscle-contraction.htm http://health.howstuffworks.com/human-body/systems/musculoskeletal/muscle2.htm
explain a muscle contraction