Ulna
Long bone of the forearm, medial to the radius.
The ulna is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the radius, the forearm's other long bone. Longer and thinner than the radius, the ulna is considered to be the smaller long bone of the lower arm.
- type
- Bone
- location
- Forearm, medial side
- articulations
- Humerus, radius, triangular articular disk
- processes
- Olecranon, coronoid, styloid
- notches
- Semilunar, radial
Lore & Background
The ulna is a long bone found in the forearm that stretches from the elbow to the wrist, and when in standard anatomical position, is found on the medial side of the forearm. It is broader close to the elbow, and narrows as it approaches the wrist. Close to the elbow, the ulna has a bony process, the olecranon process, a hook-like structure that fits into the olecranon fossa of the humerus, preventing hyperextension and forming a hinge joint with the trochlea of the humerus. There is also a radial notch for the head of the radius, and the ulnar tuberosity to which muscles attach. Close to the wrist, the ulna has a styloid process.
Reader's Guide
The ulna is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the radius, the forearm's other long bone. Longer and thinner than the radius, the ulna is considered to be the smaller long bone of the lower arm. The corresponding bone in the lower leg is the fibula. The ulna's structure includes the olecranon and coronoid processes near the elbow, which articulate with the humerus, and the styloid process near the wrist. Its body has three borders and three surfaces, providing attachment for muscles such as the flexor digitorum profundus, pronator quadratus, and extensor carpi ulnaris. The head of the ulna articulates with the triangular articular disk and the ulnar notch of the radius.
Did You Know?
- The ulna is longer and thinner than the radius.
- The olecranon process prevents hyperextension of the elbow.
- The ulna has a styloid process near the wrist.
- The corresponding bone in the lower leg is the fibula.
Frequently Asked Questions
What is the Ulna?
The ulna is one of the two long bones of the forearm, sitting on the medial (little-finger) side. It stretches from the elbow region down to the wrist, running alongside the radius.
Where exactly is the Ulna positioned in the arm?
It occupies the medial compartment of the lower arm, meaning it lies on the same side as your pinky finger. It runs parallel to the radius, though it is generally longer and slimmer than that companion bone.
What joints does the Ulna participate in?
The ulna articulates with the humerus at the elbow, connects with the radius, and interfaces with the triangular articular disk near the wrist.
What are the Ulna's key bony landmarks?
Its three notable processes are the olecranon (the bony point of the elbow), the coronoid process, and the styloid process at the wrist end. The bone also bears two named notches: the semilunar notch and the radial notch.
How does the Ulna differ from the Radius?
Although the ulna is often described as the smaller forearm bone, it is actually the longer and thinner of the pair. The two bones run parallel to one another, with the ulna on the medial side and the radius on the lateral side.
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