Joint Motions

The purpose of joints is to allow motion, and the motion of joints is controlled primarily by the muscles which cross them. For any given motion, the muscle which provides the bulk of the necessary power is called the prime mover. The prime mover is usually assisted by other muscles called synergists. Muscles which resist the motion of the prime mover are called antagonists. The tissue which attaches a muscle to a bone may be called a tendon or an aponeurosis. A tendon is a narrow cord of tough connective tissue, whereas an aponeurosis is a broad sheet of tissue. The tendon or aponeurosis is continuous with the fibrous fascia which wraps around muscles.

Often when a muscle acts on a joint, one end of the muscle remains fixed while the other end moves. In such cases, the end of the muscle which is fixed is called the origin, whereas the end of the muscle which moves is called the insertion.

The motions of joints may be described by specific terminology. For example, a motion which takes a component of the joint away from the midline of the body, such as holding the arms out at ones`s sides, is called abduction. A motion which brings a component of the joint towards the midline of the body is called adduction. A motion which creates a more acute angle (a smaller angle) between the bones of a joint is called flexion. For example, bending the fingers to make a fist requires flexion of the interphalangeal and metacarpophalangeal joints. A motion which creates a more obtuse angle (larger angle) between the bones of a joint is called extension. Opening the hand requires extension of the interphalangeal and metacarpophalangeal joints. By common agreement, however, bringing the arms forward and parallel to the floor is called flexion of the shoulder, whereas bringing the arms behind the back is called extension of the shoulder.

There are two types of circular motion. Swinging a long bone in a large circle around a joint, for example swinging the arms in a circle around the shoulder, is called circumduction. However, rotation refers to motion around the axis which runs along the long bone of a body part. For example, keeping the legs straight but turning the foot inward and outward causes rotation of the hip joint.

Special terms describe motions which are unique to the hands and feet. Supination refers to rotating the arms to bring the palms of the hands upward (superior). Pronation refers to rotating the arms to bring the palms of the hands downward. Turning the soles of the feet inward to face each other is called inversion. Turning the soles of the feet outward so that they face away from each other is called eversion. Flexing the ankle so that the foot rises off of the ground is called dorsiflexion. The opposite motion, straightening the ankle so that the toes point inferiorly, is called plantar flexion (even though it would seem more logical to call this motion extension).

 

English - Japanese Glossary

abduction: 外転 (gaiten); adduction: 内転 (naiten); antagonist: 拮抗筋 (kikkoukin); aponeurosis: 腱膜 (kenmaku); circumduction: 分廻し (funmawashi); dorsiflexion: 背屈 (haikutsu); eversion: 外反 (gaihon); extension: 伸展 (shinten); external (outward) rotation: 外旋 (gaisen); fascia: 筋膜 (kinmaku); flexion: 屈曲 (kukkyoku); insertion: 停止 (teishi); internal (inward) rotation: 内旋 (naisen); inversion: 内反 (naihon); muscle: 筋肉 (kinniku); origin: 起始 (kishi); plantar flexion: 低屈 (teikutsu); prime mover (protagonist): 主動筋 (shudoukin); pronation: 回内 (kainai); rotation: 回転 (kaiten); supination: 回外 (kaigai); synergist: 共力筋 (kyouryokukin); tendon: (ken)

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