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Muscles have two types of nerves.
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Motor nerves (nerves related to
movement): Each motor nerve sends impulses from the central nervous
system (CNS) to the termination point on a muscle fiber, called the
motor end plate, resulting in a muscle contraction.
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Sensory nerves: These nerves relay
information about pain and body orientation from the body to the
central nervous system (CNS).
A muscle consists of special fibers,
which range in length from a few inches to over three feet, and extend
over the entire length of the muscle. These fibers are grouped in
bundles called fasciculi, each separately wrapped in a sheath (perimysium)
that holds it together.
Each muscle fiber has thread-like
protein strands called myofibrils, which hold the contractile proteins
myosin (thick filaments) and actin (thin filaments), whose actions are
very important in muscle contraction. The ability of a muscle to
contract and exert force is determined by its design, the
cross-sectional area, the fiber length, and the number of fibers within
the muscle. Genetics determines the number of fibers within the muscles,
and training will not affect this, but training will have an impact on
the other variables. Dedicated training increases the thickness of these
muscle filaments, which increases both muscle size and force of
contraction.
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