The humerus is the long bone of the upper arm of human beings and other tetrapod vertebrates. This bone originates from the shoulder blade known as the scapula and ends at the elbow.
The anatomy of the humerus
In terms of structure, the humerus serves as a connection between the scapula and the elbow, where it links to the two lower arm bones. The humerus consists of three sections, such as:
The upper extremity of the humerus which contains a rounded head, two necks (the anatomical neack and the surgical neck), and a couple short processes, known as tuberosities (the greater tuberosity and the lesser tuberosity).
The body or the shaft of the humerus
The lower extremity of the humerus which articulates with the two lower arm bones, the radius and the ulna.
Formed slightly less than a sphere, the head of the humerus faces upwards, inwards and backwards, and is covered by hyaline cartilage. It articulates with the glenoid fossa of the scapula. The anatomical neck refers to the slight narrowing just behind the head, while the surgical neck refers to the first constriction on the first shaft below the expanded portion of the head. The lesser tuberosity projects forward from just beyond the anterior portion of the anatomical neck; while the greater tuberosity is the most lateral portion of the proximal section of the humerus, and is responsible for the rounded contour of the shoulder.
The body or the shaft of the humerus is quite cylindrical in its upper portion and becoming a little more triangular in its lower portion. About mid-way down the lateral aspect of the shaft, is the deltoid tuberosity, a slightly roughened surface where the deltoid muscle is inserted.
The lower extremity of the humerus contains the articulations for the two lower arm bones – the radius and the ulna. On its lateral and anterior part lies the capitulum, a small hemisphere which articulates with the head of the radius. On the anterior middle-third portion lies the pulley-shaped trochlea, which articulates with the olecranon process, the trochlear notch of the ulna. The distal end of the humerus also contains the medial and the lateral epicondyles, the structures that provide attachments for the forearm muscles.
The function of the humerus
The humerus links the elbow to the shoulder blade. It provides support to the major muscles of the shoulder, the upper arm, as well as the lower arm. It also provides anchor to three nerves, namely: the axillary, the radial and the ulnar nerves, which are vital in the function of the shoulder, the upper arm, and the forearm. Because of its structure and physiology, the humerus is indeed very important in the proper functioning and movement of the entire arm. Fractures in any section of the humerus can lead to damage or loss of certain essential functions of the shoulder, the arm and the hand.
