Sarcomere

Sarcomere - A segment of a myofibril (muscle cell) from one Z disk to the next.  This is the smallest functional unit of a muscle cell. A muscle shortens because all of the individual sarcomeres shorten, pulling Z disks closer to one another. Example: A sarcomere is the smallest functional unit of a muscle cell, discussed when teaching contractile proteins, the sliding filament theory and length/tension relationships.

1. Saladin, K. (2014). Anatomy & physiology: The unity of form and function. McGraw-Hill Higher Education, New York. ISBN: 9780073403717