A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a
muscle fiber generates tension through the action of
actin and
myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten or remain the same. Though the term 'contraction' implies a shortening or reduction, when used as a scientific term referring to the muscular system contraction refers to the generation of tension by muscle fibers.
Locomotion in most higher animals is possible only through the repeated contraction of many
muscles at the correct times. Contraction is controlled by the central nervous system, which comprises the
brain and
spinal cord. Voluntary muscle contractions are initiated in the brain, while the spinal cord initiates involuntary
reflexes.
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