182 Anatomy & Physiology Essentials Copyright Goodheart-Willcox Co., Inc. radial deviation, and adduction of the hand toward the little finger is called ulnar deviation. Trunk and neck motions directed away from ana- tomical position in the frontal plane are called lateral flexion and side bending. Movement that returns from a position of lateral flexion to the anatomical position is called lateral extension. Movements in the Transverse Plane Transverse plane movements involve rotation that is directed largely around the long axis of a body segment. When the head or trunk rotates from side to side, the movement is simply called left or right rotation. Rotation of an arm or a leg in the transverse plane is called medial rotation if the rotation is directed medially (inward), or lateral rotation if the movement is directed laterally (outward). The terms used for rotation of the forearm are pronation for medial (palm down) rotation and supination for lateral (palm up) rotation. Movements in Multiple Planes A few movements of body segments do not fall within a single plane. If you have ever purchased running shoes, you may have heard the terms pronation and supination used to describe motions of the foot occurring specifically at the subtalar joint (where the heel and ankle bones meet). Pronation at the subtalar joint is a combination of eversion, abduction, and dorsiflexion. Supination at this joint includes inversion, adduction, and plantar flexion. Moving a finger, arm, or leg in a rotational manner such that the end of the segment traces a circle is called circumduction. Finally, touching any of your four fingers to the thumb is known as opposition. Having an opposable thumb gives humans the all-important ability to grasp objects. Two movements of the foot also occur primarily in the sagittal plane. Bringing the top of the foot toward the lower leg is called dorsiflexion, and moving the foot in the opposite direction, away from the lower leg, is called plantar flexion. Understanding Medical Terminology Planting the ball of the foot is the motion involved in plantar flexion. Movements in the Frontal Plane Common movements in the frontal plane include abduction and adduction. Abduction includes move- ments at the shoulder and hip that take the arm and leg away from the midline of the body. In contrast, adduction refers to movements that bring the arm and leg closer to the midline of the body. Understanding Medical Terminology Just as abduct means “to take away,” abduction takes a body segment away from the body. Just as add means “to bring back,” adduction returns a body segment closer to the body. Movements of the foot known as inversion and eversion occur mainly in the frontal plane. Rolling the sole of the foot inward is inversion, and rolling the sole of the foot outward is eversion. Recall that the forearm has two bones: the radius and the ulna. The radius is on the thumb side of the hand, and the ulna is on the “little finger” side. From the anatomical position, with the palms facing forward, abduction of the hand toward the thumb is called SECTION 6.2 REVIEW Mini-Glossary abduction movement of a body segment away from the body in the frontal plane acetylcholine a neurotransmitter that stimulates muscle action potential the electric charge produced when a nerve or muscle fiber is stimulated adduction movement of a body segment closer to the body in the frontal plane all-or-none law a rule stating that the fibers in a given motor unit always develop maximum tension when stimulated axon a long, thin fiber connected to the cell body of a motor neuron axon terminals offshoots of the axon that branch out to connect with individual muscle fibers circumduction rotational movement of a body segment such that the end of the segment traces a circle (continued)