More specialised components
of Muscle Fibres/cells:
The components of skeletal muscle cells that are specific
to muscle tissue are called myofibrils.
These are cylindrical structures (illustrated above) that extend along
the complete length of the muscle fibre/cell.
Each myofibril consists of two types of
protein filaments called "thick
filaments", and "thin
filaments".
These two types of filament have different structures
- as illustrated on the page about labeled
diagrams of muscle filaments.
Here, it is sufficient to say that the thick filaments and
the thin filaments within myofibrils overlap
in a structured way, forming units called sarcomeres.
Sarcomeres are sections of myofibril
that are separated from each other by areas of
dense material called "Z
discs".
The sarcomeres are also described
in terms of the bands/zones within which one or
both of the two filaments occur.
These bands/zones are illustrated in the diagram below:
The "A
band" is a relatively darker area within
the sarcomere that extends along the total length
of the thick filaments.
The "H
zone" is at the centre of the A
band of each sarcomere.
As shown below, this is the region in which there
are only thick filaments, and no thin filaments.
The "I
band" is the region between adjacent
A bands, in which there are only
thin filaments, and no thick
filaments.
( Each I band extends across two adjacent sarcomeres.)
In the diagram below the Z
discs are represented by the zig-zag
lines that form the boundaries between adjacent sarcomeres. |
