Answer
The movements possible at synovial joints are divided into fourlarge groups:
1. Gliding
2. Angular movements
3. Rotation
4. Special movements
Work Step by Step
Movement at synovial joints
1. Gliding movements
In this kind of movement, relatively flat bones in a joint move back and forth or from side to side with respect to each other. Examples are movements between carpal bones and between ankle bones.
2. Angular movements. This is the best known class. In this class of movements the essential criterion is that during movement, the angle between the two bones of the joint increases or decreases. Some of these well known movements are flexion , extension, adduction and abduction. In a adduction the angle decreases and the body part ( eg upper limb) is drawn towards the anatomical midline. In abduction the angle between the bones involved increases as the body part( e.g. lower limb) is moved away from the anatomical midline. Other angular movements are flexion, extension and circumduction.
3. Rotation. In this class of movement a bone rotates around its longitudinal axis. An example of the type of this type of joint is the atlanto-axial joint . We do this rotation when we shake our heads in the nonverbal gesture for "No." Limbs may be rotated laterally (away from), or medially ( toward) with respect to the anatomical midline.
4. Special movements comprise the largest and most diverse category. It includes elevation, depression, protraction, retraction, inversion, eversion, pronation, supination, dorsiflexion, plantar flexion, and opposition. An example of dorsiflexion of the foot is standing on one's heels. Plantar flexion is standing on tip toes.
