Computational Intelligence in Analysis of Electromyography Signals - Computational Intelligence in Biomedical Engineering - page 211

Perimysium

Bone

Blood
vessels

Endomysium

Muscle
fiber
(cell)

Epimysium

Fascicle

Tendon

Endomysium

FIGURE 5.2
Cross-section of skeletal muscle and connection to the bone via tendons.
(Courtesy of http://people.eku.edu/ritchisong/301notes3.htm.)

iodine. On closer inspection, we find that skeletal muscles have a striated or
striped appearance, which is a unique characteristic of this type of muscle. The
appearance is caused by numerous sarcomere filaments. Skeletal muscles are
attached to bones by tendons, connective tissue ensheathed in a layer known as
the epimysium . The muscles groups are composed of fascicles , which are fiber
bundles surrounded by a layer called the perimysium as seen in Figure 5.2.
The cell membrane of each muscle fiber is known as the sarcolemma , which
acts as a conductor for impulses, much like neurons do for nerve impulses. The
muscle cells (see Figure 5.3) are composed of myofibrils that are bundles of
sarcomeres. Sarcomeres are multiprotein complexes composed of three types
of myofilaments called actin, myosin, and titin. Actin is a protein monomer
that forms thin filaments in the sarcomere whereas myosin forms thick fila-
ments. Each thick myofilament is surrounded by six thin myofilaments. The
elastic system of the muscle is composed of the large protein structure titin
(or connectin). The sarcomere is defined as the segment in between two
Z-lines that are actually formed by overlapping myofilaments and appear
as dark and distinct bands in electron micrographs. The region around the
Z-lines is known as the isotropic band (I-band) and the region in between the
Z-lines is the anisotropic band (A-band). Within the A-band itself is a paler
H-band composed of M-lines. The I-band is mainly composed of actin fila-
ments whereas the A-band contains myosin filaments. The interaction between
actin and myosin filaments together with calcium ions provides the contrac-
tion properties of muscle. The interaction between these components is com-
monly referred to as the sliding cross-bridge system, which will be described
in greater detail later.