Skeletal Muscle Structure

Structure of Muscle

• 1 muscle = several fibre bundles
• 1 bundle = several muscle fibres
• 1 muscle fibre = several myofibrils
• 1 myofibril has several actin & myosin filaments arranged in end-to-end sarcomeres

Actin

• actin is the thin myofibril. It contains two main divisions:
• G-actin: the orange balls that actually do the binding to the myosin myofilaments.
• Tropomyosin: the rope structure that covers and uncovers the myosin binding sites. It is held in the "covered" position using troponin. If Ca+ is present, it inhibits troponin binding, which leaves the G-actin available for myosin binding.
• REMEMBER: the difference between G-actin and tropomyosin - Trop is a rope.

Myosin

• Myosin is the thick myofibril. It is made up of many myosin molecules.
• myosin molecules have heads that will bind to the actin and then move to contract the muscle.
• ANALOGY: just light flexing your bicep, the myosin head acts the same when doing a power stroke.
• REQUIRES ATP TO FUNCTION