Answer
A sarcomere is a segment of a myofibril from Z-disc to Z-disc. It is the functional contractile unit of the muscle fiber.
A muscle fiber shortens because its individual sarcomeres shorten pulling Z-discs closer together; at the same time dystrophin and linked proteins pull on the extracellular proteins of the muscle fiber.
Work Step by Step
As Z-discs are pulled closer together, they pull on the sarcolemma to achieve overall cell shortening.
