Muscular Biopolymers - Engineered Biomimicry - page 138

physiological characteristics of human or mam-
malian muscles.
Muscles provide the movement capability
of the human body and form 40-45% of body
weight. They provide a means of direct con-
version of chemical to mechanical (movement,
work, and force) energy. Myology deals with the
scientific study of muscle.
There are three distinct types of muscle tissue
that vary in microscopic anatomy and nervous
controls. These are skeletal, cardiac, and smooth
muscles.
Skeletal muscle tissues are primarily attached
to bones and provide for the movement of the
skeleton. They are striated; alternating light and
dark bands are visible when the tissue is exam-
ined under a microscope. They are also classi-
fied as voluntary muscle tissue since they are
under conscious control.
Cardiac muscle tissue is found in the heart
only. It is also striated but involuntary, that is,
its contraction is usually not under conscious
control and uses a pacemaker included in the
muscle to produce a heartbeat.
Smooth muscle tissue is found in the walls of
hollow internal structures such as blood vessels,
the stomach, the intestines, and most abdominal
organs. It is nonstriated and involuntary.
There are three basic functions of muscle tis-
sue by contraction or alternating contraction
and relaxation: producing motion, providing
stabilization, and generating heat.
There are four functional characteristics of the
muscle as follows:

3. Extensibility , or the ability of the muscle to
be extended (stretched) without damaging
the tissue. Most skeletal muscles are
arranged in opposing or antagonistic pairs
in which one muscle tissue contracts
while the other one is relaxed or even
stretched.
4. Elasticity , or the ability of the muscle tissue
to return to its original shape after
stimulation [1] .

Nerves and blood vessels supply muscle in
abundance. Motor neurons are responsible for
stimulating muscle fibers. In order for muscle
tissue to contract, it uses a good deal of adeno-
sine triphosphate (ATP), an energy-rich mole-
cule, and it has to produce ATP by inflow of
nutrients and oxygen brought about by the
blood capillaries (microscopic blood vessels)
that are found in abundance in muscle tissue.
Each muscle fiber (cell) is in close contact with
one or more capillaries.
Connective tissue surrounds and protects
muscle tissue. Fascia is a sheet of broadband
fibrous connective tissue beneath the skin,
around the muscles and other organs in the
body. Deep fascia, a dense irregular connective
tissue, lines the body wall and extremities, holds
muscles together, and separates them into func-
tional groups. Deep fascia allows free move-
ment of muscles; carries nerves, blood, and
lymphatic vessels; and fills spaces between mus-
cles. Beyond deep fascia are three layers of
dense, irregular connective tissues that further
protect and strengthen skeletal muscle.
The outermost layer encircling the whole
muscle is the epimysium . Perimysium then sur-
rounds bundles ( faciculi or fascicles ) of 10-100 or
more individual muscle fibers. Further penetrat-
ing the interior of each individual fascicle and
separating muscle fibers from one another is the
endomysium . Interested readers are invited to
read Appendix A of Ref. 1 .
A motor neuron delivers the stimulus that
ultimately causes a muscle fiber to contract.

1. Excitability , or the ability to respond to certain
stimuli by producing action potentials or
impulses of electrical signal. The stimuli
triggering action potentials are chemicals
such as neurotransmitters released by neu-
rons or hormones distributed by the blood.
2. Contractility , or the ability to contract and
generate force to do work. Contraction is in
response to one or more muscle action
potentials.