1.10. Muscles, Bones, and Movement http://www.ck12.org
1.10 Muscles, Bones, and Movement
- Describe how skeletal muscles and bones work together to move the body.
Do muscles come in pairs?
This woman is doing a stretch for the muscles on the back of her legs, the hamstrings. She also has a muscles on the
front of her legs, directly opposite the hamstrings. These are the quadriceps. The hamstrings and quadriceps work
together as a pair to move your legs back and forth while you run.
Muscles, Bones, and Movement
Skeletal muscles are attached to the skeleton by tendons. Atendonis a tough band of connective tissue that connects
a muscle to a bone. Tendons are similar to ligaments, except that ligaments join bones to each other.
Muscles move the body by contracting against the skeleton. When muscles contract, they get shorter. By contracting,
muscles pull on bones and allow the body to move.
Muscles can only contract. They cannot actively extend, though they can move back into the non-contracted neutral
position. Therefore, to move bones in opposite directions, pairs of muscles must work in opposition. Each muscle
in the pair works against the other to move bones at the joints of the body. The muscle that contracts to cause a joint
to bend is called theflexor. The muscle that contracts to cause the joint to straighten is called theextensor. When
one muscle is contracted, the other muscle from the pair is always elongated.
For example, the biceps and triceps muscles work together to allow you to bend and straighten your elbow. When
you want to bend your elbow, your biceps muscle contracts (Figure1.19), and, at the same time, the triceps muscle
relaxes. The biceps is the flexor, and the triceps is the extensor of your elbow joint.