Summary Physiology; Skeletal muscle - contraction review

14/03/19

Professor Maurice Elphick

Skeletal Muscle Contraction
Sarcomeres – contractile units

• Have thick and thin filaments
o Cross bridges go from thick to thin filaments
o I band gets smaller, A band doesn’t change

Sliding Filament Theory

• H.E. Huxley and A.F Huxley 1954
• Forge generated is maximal with maximal overlap
o Of thick and thin filaments

Key points:

1) Cross bridges between thick and thin filaments
2) Thick and thin filaments don’t change length, they slide
3) Extent of interaction determines force power

Thin Filaments

• 2 helical strands of filamentous actin (F)
o Troponin and tropomyosin

Thick Filaments

• Myosin complexes
o 2 supercoiled alpha helices
o Amino and carboxyl termini
o Myosin light chains

Ca2+ Release

• From sarcoplasmic reticulum
• Ca2+ binds with troponin, breaking bond with actin and exposing myosin
1) Myosin head bound to actin monomer via cross bridge
a. Myosin head also attached to ADP and phosphate
2) Power stroke – ADP and Pi released, cross bridges bend and filaments slide past each other
3) ATP energy releases myosin head from actin
4) Hydrolysis of ATP returns myosin head to actin
5) Myosin head attaches to new actin monomer now

Other Muscle Proteins

• Titin is the largest protein in humans
o 34,350 amino acid residues
o Located between Z line and thick filament
o Confers elasticity on muscle – springs back after contraction
▪ Template for assembly of contractile machinery in muscle