Organized Thick and Thin Filaments in Skeletal Muscle Slide Past One Another During Contraction

Muscle cells have evolved to carry out one highly specialized function—contraction. Muscle contractions must occur quickly and repetitively, and they must occur through long distances and with enough force to move large loads. A typical skeletal muscle cell, called a myofiber, is cylindrical, large (1-40 mm in length and 10-50 ^m in width), and multinucleated (containing as many as 100 nuclei). The cy-

(a) Myosin filaments

Actin filaments Actin filaments

Actin filaments Actin filaments

AI zone H zone AI zone — I band—-A band->k-I band —

Sarcomere

I_1 [im toplasm is packed with a regular repeating array of filament bundles organized into a specialized structure called a sar-comere. A chain of sarcomeres, each about 2 ^m long in resting muscle, constitutes a myofibril. The sarcomere is both the structural and the functional unit of skeletal muscle. During contraction, the sarcomeres are shortened to about 70 percent of their uncontracted, resting length. Electron microscopy and biochemical analysis have shown that each sarcomere contains two types of filaments: thick filaments, composed of myosin II, and thin filaments, containing actin (Figure 19-22).

(b) Myosin filaments

Actin filaments Actin filaments
10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

Get My Free Ebook


Post a comment