Snigdha Goswami

Sliding Filament Theory:  The sliding filament theory explains the mechanism of muscle contraction based on muscle proteins that slide past each other to generate movement. According to the sliding filament theory the myosin filaments of muscle fibres slide past the actin thin filaments during muscle contraction while the two groups of filaments remained at relatively constant at length.  1. I bands are composed of actin filaments and the A Bands principally of myosin filaments. 2. during muscle contraction the actin filaments move into the A bands between the myosin filaments. 3. The backbone of a muscle fibre is actin filaments which extend from z line up to one end of H zone, where they are attached to an elastic component which is named as S filament. 4. Myosin filaments extend from one end of the A band through the H zone up to the other end of the A band. 5. Myosin filaments remain in relatively constant length during muscle stretch or contraction. 6. During stretching only I ban

Molecular basis of sliding filament theory :  The contraction of skeletal muscle generates the force necessary to move the Skeleton. A contraction is triggered by a series of molecular events known as cross Bridge cycle. I n a skeletal muscle fibre the function of unit contraction is called sarcomere.  A sarcomere shortens when myosin head in thick myofilament forms cross bridges with actin molecules. 1. initiation  :  the formation of a cross Bridge is initiated when calcium ions, released from the sarcoplasmic reticulum binds to troponin. This binding causes troponin to change shape. Tropomyosin moves away from the myosin binding site on actin allowing myosin head to bind and form a cross Bridge. 2. activation   of myosin head :  Activation of myosin head occurs when ATP binds to myosin head and is hydrolysed to ADP and inorganic phosphate. The energy liberated activate the myosin head forcing it into the curved position. 3. Cross Bridge formation :  The activated myosin head binds