The human skeletal system is highly complex. It contains over 200 bones, almost all of which are vital to the ability to move about. Without a skeleton, you would mostly resemble a shapeless blob – which could be somewhat annoying. There are several important bones in the arm. In the forearm, there are two major bones – the radius and the ulna. This article will look at the anatomy of the ulna.
The ulna is located in the forearm. It is on the medial side of the forearm when the arm is in the anatomical position. To the lateral side of the ulna is the radius, which is the other long bone in the forearm. The radius and ulna run parallel to each other along their entire lengths.
The proximal end of the ulna articulates with the humerous to form the elbow joint. It articulates with the radius near the elbow joint as well. This connection with the radius helps the two bones move in unison properly when the forearm is twisted (like what happens when you work a screwdriver).
The part of the ulna that attaches to the humerus to form the elbow joint is called the olecranon process. Also on the proximal end is a coronoid notch and the radial notch.
On the wrist end of the forearm, the ulna attaches to the radius again, this time at a location called the ulnar notch. Although the radius and ulna to not make direct contact other than at the ends, there is a membrane (called the interosseous membrane) that runs between the two bones along the entire length of the forearm. This membrane provides support for the forearm.
There are numerous muscles that attach to the ulna at various points. In order for a muscle to move a joint, it must cross that joint. That means the muscle that move the ulna (and forearm) are not actually located in the forearm. The muscles in the forearm itself are mostly used to move the wrist and fingers. For more information on the muscles that attach to the ulna, read THIS ARTICLE.
The far wrist end (called the distal end) of the ulna is referred to as the styloid process. This end has attachments with a tendon from a muscle called the extensor carpi ulnaris – which is responsible for extending the wrist (bending it back). The ulnar collateral ligament also attaches here.
The ulna is a bone that is commonly fractured. Because of it’s location and vulnerability, it is clinically a very important bone. The ulnar nerve runs the length of the ulna. As this nerve crosses the elbow joint, it runs very near the surface. It’s the nerve that is irritated when you hit your elbow on the “funny bone”. There is no actual “funny bone”, it’s the ulnar nerve you’ve wacked. This isn’t directly related to the ulna, but it’s an interesting bit of party trivia.
