What are muscles made up of?

What are muscles made up of?

• A. Nerves
• B. Muscle fibers
• C. Cartilage
• D. Bone marrow

Answer: (B)

Muscles are made up of muscle fibers, which are the long, contractile cells that actually shorten to produce movement. Each muscle fiber contains myofibrils, made of actin and myosin arranged into sarcomeres—the tiny units that drive contraction. These fibers group together into bundles called fascicles, and many fascicles form the whole muscle, all wrapped in connective tissue and supplied by nerves and blood vessels. The other options aren’t the material of muscle: nerves transmit signals to trigger contraction, cartilage cushions joints, and bone marrow lies inside bones and produces blood cells.

Muscles are made up of muscle fibers, which are the long, contractile cells that actually shorten to produce movement. Each muscle fiber contains myofibrils, made of actin and myosin arranged into sarcomeres—the tiny units that drive contraction. These fibers group together into bundles called fascicles, and many fascicles form the whole muscle, all wrapped in connective tissue and supplied by nerves and blood vessels. The other options aren’t the material of muscle: nerves transmit signals to trigger contraction, cartilage cushions joints, and bone marrow lies inside bones and produces blood cells.