Sliding Filament Theory

1130 Words Nov 5th, 2010 5 Pages
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
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sarcomeres are divided to show

how the sections move during a contraction. The Z line is in the middle of the I bands

and notes the separation of each sarcomere. The I band is light colored because it only

contains the thin filaments actin. The A band contains overlapping actin and myosin,

and the H zone only has myosin filaments. The M line is in the middle of the sarcomere

and is where the myosin filament is free of cross bridges.

Sliding Filament Theory

The sliding filament theory was first introduced over 50 years ago. Hugh Huxley

and Allan Huxley conducted two independent studies and published them in May 1954.

The theory has been added to, but remains relatively the same to this day.

Before the sliding filament theory, it was widely accepted by most academics that

the protein myosin contracted with the presence of calcium ions. The actin proteins roll

had not yet been realized. The 1954 theory states that the filaments containing the proteins myosin and

actin “slid” past each other and neither filament changed in length. In 1957 Allan Huxley

added that the myosin has a cross bridge structure that binds, rotates and detaches

from the actin. He also states when energy is released from the conversion of ATP to

ADP it creates a power stroke that moves the filaments past each other. (6)

How the Filaments “Slide”

Movement begins when an action potential (electrical
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