Question

Each muscle fiber contains tiny threads called _____, which are made of myosin and actin.

ligaments
myofibrils
myoactin
ATP

Answer 1

Myofibrils are the building blocks or contractile unit of each muscle fiber. The tiniest functional unit of skeletal muscle, the sarcomere, is found in the myofibrils and is made up of protein filaments: actin (thin) and myosin (thick).