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The Muscular System

6 THE MUSCULAR SYSTEM

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Overview

T he muscular system is the biological system of humans that allows them to move. The muscular

system, in vertebrates, is controlled through the nervous system, although some muscles, like
cardiac muscle, can be completely autonomous.

Muscle is contractile tissue and is derived from the mesodermal layer of embryonic germ cells. Its
function is to produce force and cause motion, either locomotion or movement within internal organs.
Much of muscle contraction occurs without conscious thought and is necessary for survival, like the
contraction of the heart or peristalsis, which pushes food through the digestive system. Voluntary
muscle contraction is used to move the body and can be finely controlled, such as movements of the
finger or gross movements that of the biceps and triceps.

Muscle is composed of muscle cells (sometimes known as "muscle fibers"). Within the cells are
myofibrils; myofibrils contain sarcomeres which are composed of actin and myosin. Individual muscle
cells are lined with endomysium. Muscle cells are bound together by perimysium into bundles called
fascicles. These bundles are then grouped together to form muscle, and is lined by epimysium. Muscle
spindles are distributed throughout the muscles, and provide sensory feedback information to the
central nervous system.

Skeletal muscle, which involves muscles from the skeletal tissue, is arranged in discrete groups.
An example of which includes the biceps brachii. It is connected by tendons to processes of the
skeleton. In contrast, smooth muscle occurs at various scales in almost every organ, from the skin (in
which it controls erection of body hair) to the blood vessels and digestive tract (in which it controls the
caliber of a lumen and peristalsis).

There are approximately 650 skeletal muscles in the human body (see list of muscles of the human

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