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|Anatomical terms of motion|
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Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used, describes this motion according to its direction relative to the anatomical position of the joints. Anatomists use a unified set of terms to describe most of the movements, although other, more specialized terms are necessary for describing the uniqueness of the movements such as those of the hands, feet, and eyes.
In general, motion is classified according to the anatomical plane it occurs in. Flexion and extension are examples of angular motions, in which two axes of a joint are brought closer together or moved further apart. Rotational motion may occur at other joints, for example the shoulder, and are described as internal or external. Other terms, such as elevation and depression, refer to movement above or below the horizontal plane. Many anatomical terms derive from Latin terms with the same meaning.
Motions are classified after the anatomical planes they occur in, although movement is more often than not a combination of different motions occurring simultaneously in several planes. Motions can be split into categories relating to the nature of the joints involved:
Apart from this motions can also be divided into:
The prefix hyper- is sometimes added to describe movement beyond the normal limits, such as in hypermobility, hyperflexion or hyperextension. The range of motion describes the total range of motion that a joint is able to do.  For example, if a part of the body such as a joint is overstretched or "bent backwards" because of exaggerated extension motion, then it can be described as hyperextended. Hyperextension increases the stress on the ligaments of a joint, and is not always because of a voluntary movement. It may be a result of accidents, falls, or other causes of trauma. It may also be used in surgery, such as in temporarily dislocating joints for surgical procedures. 
These are general terms that can be used to describe most movements the body makes. Most terms have a clear opposite, and so are treated in pairs.
Flexion describes a bending movement that decreases the angle between two parts. For example, bending the elbow, or clenching a hand into a fist, are examples of flexion. When sitting down, the knees are flexed. When a joint can move forward and backward, such as the neck and trunk, flexion refers to movement in the anterior direction. Flexion of the shoulder or hip refers to movement of the arm or leg forward.
Extension is the opposite of flexion, describing a straightening movement that increases the angle between body parts. When a joint can move forward and backward, such as the neck and trunk, extension refers to movement in the posterior direction. For example, when standing up, the knees are extended. Extension of the hip or shoulder moves the arm or leg backward. When the chin is against the chest, the head is flexed, and the trunk is flexed when a person leans forward. 
Abduction and adduction refer to motions that move a structure away from or towards the centre of the body. The centre of the body is defined as the midsagittal plane. These terms come from the Latin words with the same meaning.[b]
Abduction refers to a motion that pulls a structure or part away from the midline of the body. In the case of fingers and toes, it refers to spreading the digits apart, away from the centerline of the hand or foot. Abduction of the wrist is also called radial deviation. For example, raising the arms up, such as when tightrope-walking, is an example of abduction at the shoulder. When the legs are splayed at the hip, such as a star jump or doing a split, the legs are abducted at the hip.
Adduction refers to a motion that pulls a structure or part toward the midline of the body, or towards the midline of a limb. In the case of fingers and toes, it refers to bringing the digits together, towards the centerline of the hand or foot. Adduction of the wrist is also called ulnar deviation. For example, dropping the arms to the sides, or bringing the knees together, are examples of adduction.
The terms elevation and depression refer to movement above and below the horizontal. They derive from the Latin terms with the same meaning[c]
Rotation of body parts is referred to as internal or external, referring to rotation towards or away from the center of the body.
Internal rotation (or medial rotation) refers to rotation towards the axis of the body. For example, pointing the feet to face each other, or when the arms are turned so that the palms face the back of the body, are examples of internal rotation. 
External rotation (or lateral rotation) refers to rotation away from the center of the body. For example, rotation of the feet or arms in the opposite direction to that above is an example of external rotation. 
The swinging action made during a tennis serve is an example of circumduction
Dorsiflexion and plantar flexion refers to extension or flexion of the foot at the ankle. These terms refer to flexion between the foot and the body's dorsal surface, considered the front of the leg, and flexion between the foot and the body's plantar surface, considered the back of the leg. These terms are used to resolve confusion, as technically extension of the joint refers to dorsiflexion, which could be considered counter-intuitive as the motion reduces the angle between the foot and the leg. 
Dorsiflexion where the toes are brought closer to the shin. This decreases the angle between the dorsum of the foot and the leg. For example, when walking on the heels the ankle is described as dorsiflexion.
Plantar flexion is the movement which decreases the angle between the sole of the foot and the back of the leg. For example, the movement when depressing a car pedal or standing on the tiptoes can be described as plantar flexion.
A ballerina, demonstrating plantar flexion of the feet.
Palmarflexion and dorsiflexion refer to movement of the flexion (palmarflexion) or extension (dorsiflexion) of the hand at the wrist. These terms refer to flexion between the hand and the body's dorsal surface, which is the back of the arm, and flexion between the hand and the body's plantar surface, which in anatomical position is considered the anterior side of the arm. The direction of terms are opposite to those in the foot because of embryological rotation of the limbs in opposite directions.
Pronation at the forearm is a rotational movement where the hand and upper arm are turned inwards. Pronation of the foot refers to turning of the foot outwards, so that weight is borne on the medial part of the foot.
Inversion and eversion refer to movements that tilt the sole of the foot away from (eversion) or towards (inversion) the midline of the body.
Eversion is the movement of the sole of the foot away from the median plane. Inversion is the movement of the sole towards the median plane. For example, inversion describes the motion when an ankle is twisted.
Unique terminology is also used to describe the eye. For example:
Other terms include:
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