Which best describes X and Y?
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Answer:
Muscles at the microscopic level are made of actin (thin filament) and myosin (thick filament) fibers in alternation and parallel to each other. During contraction, the fibres seem to slip against each other in opposite directions. Technically, the myosin head ‘walks’ on the actin – in an engage and release motion – with the help of ATP. Several actin and myosin fibers make up a myofibril. Each contractile unit in the myofibril is called a sarcomere – viewed as Z-discs at the microscopic level.
