Anatomical terms of motion
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 body parts involved. Anatomists and others use a unified set of terms to describe most of the movements, although other, more specialized terms are necessary for describing unique 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", describe movement above or below the horizontal plane. Many anatomical terms derive from Latin terms with the same meaning. Classification. 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 study of movement in the human body is known as kinesiology. A categoric list of movements and the muscles involved can be found at list of movements of the human body. Abnormal motion. 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. Or it may be used as a pain compliance method to force a person to take a certain action, such as allowing a police officer to take him into custody. General motion. 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 and extension. Flexion and extension describe movements that affect the angle between two parts of the body. These terms come from the Latin words with the same meaning. Flexion describes a bending movement that "decreases" the angle between a segment and its proximal segment. For example, bending the elbow, or clenching a hand into a fist, are examples of flexion. When a person is sitting down, the knees are flexed. When a joint can move forward and backward , such as the neck and trunk, flexion is movement in the anterior direction. When the chin is against the chest, the neck is flexed, and the trunk is flexed when a person leans forward. Flexion of the shoulder or hip is movement of the arm or leg forward. Extension is the opposite of flexion, describing a straightening movement that "increases" the angle between body parts. For example, when standing up, the knees are extended. When a joint can move forward and backward, such as the neck and trunk, extension is movement in the posterior direction. Extension of the hip or  shoulder moves the arm or leg backward. Even for other upper extremity joints - elbow and wrist, movement behind results in extension. Except for knee, ankle, and wrist, where the distal end has to move in the anterior direction for it to be called extension. With regard to the toes, flexion means curling them downward whereas extension means uncurling them or raising them upward. Abduction and adduction. Abduction is the motion of a structure away from the midline while adduction refers to motion towards the center of the body. The center of the body is defined as the midsagittal or longitudinal  plane. These terms come from Latin words with similar meanings, "ab-" being the Latin prefix indicating "away," "ad-" indicating "toward," and "ducere" meaning "to draw or pull". Abduction is a motion that pulls a structure or part "away from" the midline of the body, carried out by one or more abductor muscles. In the case of fingers and toes, it is spreading the digits apart, away from the centerline of the hand or foot. 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 when doing a star jump or doing a split, the legs are abducted at the hip. Adduction is a motion that pulls a structure or part "towards" the midline of the body, or towards the midline of a limb, carried out by one or more adductor muscles. In the case of fingers and toes, it is bringing the digits together, towards the centerline of the hand or foot. Dropping the arms to the sides, and bringing the knees together, are examples of adduction. Adduction of the wrist is also known as ulnar deviation which moves the hand  towards the ulnar styloid (or, towards the little finger). Abduction of the wrist is also called radial deviation which moves the hand moving towards the radial styloid (or, towards the thumb). Elevation and depression. The terms elevation and depression refer to movement above and below the horizontal. They derive from the Latin terms with similar meanings Elevation is movement in a superior direction. For example, shrugging is an example of elevation of the scapula. Depression is movement in an inferior direction, the opposite of elevation. Rotation. 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 ("medial rotation" or "intorsion") is rotation towards the axis of the body, carried out by internal rotators. External rotation ("lateral rotation" or "extorsion") is rotation away from the center of the body, carried out by external rotators. Internal and external rotators make up the rotator cuff, a group of muscles that help to stabilize the shoulder joint. Special motion. Hands and feet. Flexion and extension of the foot. "Dorsiflexion" and "plantar flexion" refer to extension or flexion of the foot at the ankle. These terms refer to flexion in  direction of the "back" of the foot, which is the upper surface of the foot when standing, and flexion in direction of the sole of the foot. These terms are used to resolve confusion, as technically "extension" of the joint is dorsiflexion, which could be considered counter-intuitive as the motion reduces the angle between the foot and the leg. Dorsiflexion is 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 being in dorsiflexion. Plantar  flexion or plantarflexion 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 tiptoes. Flexion and extension of the hand. 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 in anatomical position is considered the back of the arm; and flexion between the hand and the body's "palmar" 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. "Palmarflexion" is flexion of the wrist towards the palm and ventral side of forearm. "Dorsiflexion" is hyperextension of the wrist joint, towards the dorsal side of forearm. Pronation and supination. Pronation and supination refer generally to the prone (facing down) or supine (facing up) positions. In the extremities, they refer to rotation of the forearm or foot so that in the standard anatomical position the palm or sole is facing anteriorly  when in supination and posteriorly when in pronation. As an example, when a person is typing on a computer keyboard, their hands are pronated; when washing their face, they are supinated. "Pronation" at the forearm is a rotational movement where the hand and upper arm are turned so the thumbs point towards the body. When the forearm and hand are supinated, the thumbs point away from the body. Pronation of the foot is turning of the sole outwards, so that weight is borne on the medial part of the foot. "Supination" of the forearm occurs when the forearm or palm  are rotated outwards. Supination of the foot is turning of the sole of the foot inwards, shifting weight to the lateral edge. Inversion and eversion. 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. Eyes. Unique terminology is also used to describe the eye. For example: Other. Other  terms include: