The forearm contains two long bones, the ulna and the radius, extending from the elbow to the wrist. The ulna runs parallel to the radius and provides the structure and stability necessary for many arm and hand movements. Understanding the ulna’s location relative to the hand is key to grasping its role in the body.
Locating the Ulna: The Pinky Side Connection
The ulna is located on the side of the forearm that aligns with the pinky finger. Anatomically, this is the medial side of the forearm, meaning it is closer to the midline of the body when the arm is in the standard anatomical position. The ulna extends from the elbow, where it is thickest, down to the wrist, where it is narrower.
To physically locate the ulna, trace the bone from the point of your elbow, the prominent bony projection called the olecranon process. You can follow the ulna’s long, straight shaft down toward the wrist. This shaft is relatively superficial along the back of the forearm.
The Radial Counterpart: Understanding the Thumb Side
The radius occupies the opposite side of the arm, situated on the lateral side and aligning directly with the thumb. It runs parallel to the ulna; while the ulna is longer, the radius is thicker at the wrist end, where it plays a larger role in forming the wrist joint.
The radius allows for the twisting motion of the forearm, which changes the position of the hand. The Radius is on the side of the thumb, and the Ulna is on the side of the pinky finger. While the ulna provides a fixed hinge at the elbow, the radius is designed to rotate around the ulna to facilitate movements like turning a doorknob.
Function and Articulation of the Ulna
The ulna’s primary role is to create a stable hinge joint at the elbow. Its upper end features a specialized, wrench-shaped structure called the trochlear notch. This notch fits securely around the trochlea of the humerus, the upper arm bone, providing the stability necessary for bending and straightening the arm.
The olecranon process, the prominent bony point of the elbow, is part of the ulna and prevents the elbow from hyperextending. While the ulna is the dominant bone at the elbow, it contributes less directly to movement at the wrist. It articulates with the radius near the wrist but does not directly join the primary wrist bones, unlike the radius, which bears the majority of the force transmitted from the hand.