Ulna

A long bone located in the forearm, stretching from the elbow to the wrist on the inner side of the arm.

The ulna is one of the two long bones in the forearm, the other being the radius. It is located medially, meaning it is positioned closer to the body’s midline. In adults, the ulna is approximately 25 cm long, contributing to the structure of the arm and allowing for a range of movements at the elbow and wrist.

Terminologia Anatomica

ulna

System

Skeletal system

Function

The main function of the ulna is to provide structural support and stability to the forearm while facilitating movement of the elbow and wrist joints. It serves as a vital point of attachment for muscles that control wrist and finger movements. The ulna, in conjunction with the radius, enables pronation and supination of the forearm, which are essential for various daily tasks such as typing or writing. It also helps protect underlying nerves and blood vessels that run near these bones, ensuring safe and efficient function of the arm.

Location

The ulna is positioned on the inner side of the forearm, running parallel to the radius. It extends from the elbow joint down to the wrist. At the elbow, it articulates with the humerus to form a hinge joint, allowing for flexion and extension of the arm. The distal end of the ulna narrows and articulates with the carpal bones in the wrist, specifically the triangular fibrocartilage complex, providing additional stability to wrist movements. The anatomical site of the ulna makes it crucial for both strength and mobility in the arm.

Did You Know?

The ulna is often referred to as the 'anti-pronator' because it acts in opposition to the radius during forearm rotation.
In many vertebrates, the ulna has evolved uniquely to adapt to their respective modes of locomotion, such as flying in birds or swimming in seals.
The prominent bony projection at the elbow called the 'olecranon' is the proximal end of the ulna, forming its distinctive shape.