Locomotion and Movement
Locomotion and Movement tests the sliding filament mechanism, muscle types, skeleton, joints and disorders. You must link calcium, ATP and sarcomere bands to contraction.
Core rules
- Sarcomere: Z line at each end; A band contains thick myosin; I band contains thin actin; H zone is the central light region.
- Contraction: calcium binds troponin, tropomyosin moves, myosin heads bind actin, the power stroke pulls actin, and ATP detaches myosin.
- During contraction the A band stays constant while the I band and H zone shorten.
- Skeletal muscle is voluntary; smooth muscle is involuntary; cardiac muscle is involuntary and striated.
- Skeleton: axial and appendicular; joints are fibrous, cartilaginous or synovial.
- Disorders include myasthenia gravis, muscular dystrophy, gout and osteoporosis.
Worked example
In a contracted sarcomere, the A band remains the same length while the I band and H zone become narrower. Explain.
Reasoning: myosin thick filaments do not shorten. Actin thin filaments slide toward the M line, reducing the light I band and the central H zone. Answer: sliding filament theory.
Traps that cost marks
- Actin is thin; myosin is thick.
- Calcium binds troponin, not myosin.
- ATP is needed for myosin detachment and calcium reuptake.
- Rigor mortis follows ATP depletion.
- Red fibres are slow oxidative; white fibres are fast glycolytic.