How Do We Move?

Many of us go through our daily lives and activities without much thought on how

or why we move our bodies. Walking, jogging, lifting weights or even getting ourselves

out of bed in the morning requires an intricate pattern of processes that allow us to

move and access our enviroment. Our bodies move through a lever and pulley system

made up of our muscles bones and tendons acting on each other through muscle

contraction and relaxation. (1,3) To understand how a muscle contracts you must first

look at the anatomy of skeletal muscles.

Anatomy of Skeletal Muscle

Figure 1 shows the components of a cross section of muscle. Each muscle belly

is made up of thousands to tens of thousands of muscle fibers (cells). The fibers are

grouped into bundles of as many as 150 fibers called fasciculi. The bundles have a

connective tissue around them called

perimysium, and the fibers are also

surrounded by connective tissue called

endomysium.

The fibers or cells each have a

membrane called sarcolemma and

contain multi nuclei. Within the

sarcolemma membrane there are hundreds or thousands of myofibrils surrounded by

sarcoplasm. (2,3) The myofibrils are made up of two types of filaments, a thick filament

made of the protein myosin and a thin filament made up of the proteins actin and to a

lesser degree troponin and tropomyosin. The actin and myosin run parallel to each

other along the fiber. Myosin has tiny globular heads throughout the length that create

cross bridges that play an important roll in the contraction process. (4)

A Closer Look at Myofibrils

From an article in Nature

Reviews on molecular cell biology,

(4) you will see the contractile

elements of the muscle are the

myofibril. A closer look shows a

striated pattern running the