Muscular Movement Of Bones

Generally, skeletal muscles are attached to one end of a bone, stretch across a joint, and are fastened to a point on another bone. Muscles are attached to the outer membrane of bone, the periosteum, either directly or by a tough fibrous cord of connective tissue called a tendon. For example, as shown in Figure 45-13, one end of the large biceps muscle in the arm is connected by tendons to the radius in the forearm, while the other end of the muscle is connected to the scapula in the shoulder. When the biceps muscle contracts, the forearm flexes upward while the scapula remains stationary. The point where the muscle attaches to the stationary bone—in this case, the scapula—is called the origin. The point where the muscle attaches to the moving bone—in this case the radius—is called the insertion.

Most skeletal muscles are arranged in opposing pairs. One muscle in a pair moves a limb in one direction; the other muscle moves it in the opposite direction. Muscles move bones by pulling them, not by pushing them. For example, when the biceps muscle contracts, the elbow bends. The biceps muscle is known as a flexor, a muscle that bends a joint. Contraction of the triceps muscle in the upper arm straightens the limb. The triceps muscle is an example of an extensor, a muscle that straightens a joint. To bring about a smooth movement, one muscle in a pair must contract while the opposing muscle relaxes.

figure 45-13

Skeletal muscles, such as the biceps and triceps muscles in the upper arm, are connected to bones by tendons. (a) When the biceps muscle contracts, the elbow bends. (b) When the triceps muscle contracts, the elbow straightens.

Scapula

Humerus

Ulna

Scapula

Humerus

Ulna

Tendon

Biceps (flexor)

Insertion

Radius

Origin

Tendon

Biceps (flexor)

Insertion

Origin

Triceps (extensor)

Humerus

Origin

Tendon — Insertion

Was this article helpful?

0 0
31 Days To Bigger Arms

31 Days To Bigger Arms

You can have significantly bigger arms in only 31 days. How much bigger? That depends on a lot of factors. You werent able to select your parents so youre stuck with your genetic potential to build muscles. You may have a good potential or you may be like may of the rest of us who have averages Potential. Download this great free ebook and start learns how to build your muscles up.

Get My Free Ebook


Post a comment