The "Sliding-Filament
Theory of Muscle Action"
explains how the movement of thick- and thin-filaments
relative
to each other leads to the
contraction
and relaxation
of
whole
muscles - hence ultimately to the movement
of the limbs or tissues attached to those muscles:
As explained on the previous page (Structures
of Muscle Filaments), there are two physical units
that are important for the action of muscles. They are thick
filaments and thin
filaments.
Muscle tissue can be described in terms of units called
sacromeres.
These units are defined in terms of groups of overlapping
filaments (the thin and thick filaments previously
described). Sacromeres are arrangements
of thick and thin filaments.
The length of a sacromere and the zones (H
zone, I
band and A
band) within each sacromere, are determined by the
positions of the thick and thin filaments relative to each
other. This is illustrated in the three diagrams below
- showing the relative length and configuration of two
sacromeres of relaxed muscle (top), partially
contracted muscle (centre) and fully contracted
muscle (bottom diagram).
Note that although the length of the sarcomere changes,
the lengths of the filaments remain the same - the length
of the sarcomere is a consequence of the extent to which
these filaments overlap.
|
