Molecular mechanisms 

Muscles

Types of muscle tissues

Striated muscle:

makes up the skeletal muscle, heart muscle and smooth muscle. The name a as a function of the appearance in microscopic viewing.

Levels of organization

a. Muscles - made up of fascicles surrounded by connective tissue.

b. Fascicle - bundles of muscle fibres(cells).

c. Muscle fiber - composed of a bundle of myofibrils.

d. Myofibrile - composed of myofilaments responsible for force generation.

  I.) Sarcomere: smallest functional unit of muscle, made up of thin and thick filament. The titin provides the elastic behaviour of muscles.

  II.) Microfilaments: made up of actin(thin filament) and myosin(thick filament) around the myosin heads.

Motor proteins

 • Myosin II; has a head, neck and tail. The tail provides the structural integrity of the myosin, its energy source is ATP.

  • Actin; composed of actin monomers that assemble by polymerisation into actin filament.

Force generation of Sarcomere

 It is as a result of the cross-bridge cycle. ATP hydrolysis occurs and we have ADP-Pi but in this stage there is low probability of myosin binding so the cross-bridge is weak. Phosphate is then released and the myosin pulls the actin, the ATP dissociates from the myosin head so if there is no ATP in the system then myosin doesn’t detach from the actin filament.

For a normal functioning muscle we need:

DIRECTIONALITY, FORCE TRANSMISSION

REGULATION

Sliding filament theory: Z and M lines for directionality also the tendon for force transmission to bones.

Steric blocking model: Regulation by Ca, troponin and troponyosin.