Identify the structure at the end of the arrow.

Identify the structure at the end of the arrow.

• A. Myofibril
• B. Myofiber
• C. Fascicle
• D. Perineurium

Answer: (A)

Inside skeletal muscle, the slender, rod-like structures that run the length of each fiber are the myofibrils. This arrow is pointing to one of those elongated contractile units located inside the muscle cell, which collectively give the fiber its characteristic striations. A myofiber is the whole muscle cell, a fascicle is a bundle of these fibers, and the perineurium is a protective sheath around a nerve fascicle—neither matches the tiny rod-like structure shown inside the muscle fiber.

Inside skeletal muscle, the slender, rod-like structures that run the length of each fiber are the myofibrils. This arrow is pointing to one of those elongated contractile units located inside the muscle cell, which collectively give the fiber its characteristic striations. A myofiber is the whole muscle cell, a fascicle is a bundle of these fibers, and the perineurium is a protective sheath around a nerve fascicle—neither matches the tiny rod-like structure shown inside the muscle fiber.