As
mentioned earlier, the myofi
is a columnlike array of
filaments. Figure 7is a diagram of a longitudinal section
through a group of myofi
s. In the centre of the I band
(the light band, of low density) there is a prominent denseline
called the Z line, though in reality, considering the three-dimensional
structure of the myofi
, it is more appropriate to speak
of Z disks. The area between two Z lines, a sarcomere, can
be considered to be the primary structural and functional
unit directly responsible for muscle contraction. The myofi
can thus be thought of as a stack of sarcomeres. The A band,
which contains thick filaments partly overlapped with thin
filaments, appearsdark.
