Essay on the topic muscle contraction

Mechanism of muscle contraction
 Muscle is a contractile tissue helps in locomotion, maintenance of
posture.
 They serve as the biological system for converting chemical energy to
mechanical energy
 Muscle contraction is the shortening of myofibrils in response to
nervous stimulation.
 During this the actin filaments slide over myosin filaments and link with
them forming actomyosin complexes
 During muscular relaxation they delink and move away from each other

 Mechanism of Muscle contraction
o Ultrastructural changes:
o It include the regular and cyclic attachment and detachment
between the myosin cross-bridges and the actin filaments .
o It is best explained by the Sliding-Filament theory proposed by
Huxley and J.Hanson
o According to this theory, muscle fibres become short and thick
during contraction by the shortening of their sarcomeres due to
sliding of myofilaments
o Actin filaments slide inward from adjacent Z-zones to the H zone
o In the H zone they completely overlap the myosin filaments and
link with them, forming actomyosin chains
o This inward movement of actin filaments brings Z zone closer
together
o So the length of I- band and that of sarcomere(region between
two adjacent Z-zones) becomes shorter.
 Cross-bridge cycle
o The attachment- detachment cycle of the myosin head
o During muscular contraction, the head of the myosin filament
functions as a hook. It attaches to a binding site of F-actin, forming
a cross-bridge.