Humerus

The humerus (ME from Latin humerus, umerus upper arm, shoulder; Gothic ams shoulder, Greek ōmos) is a long bone in the arm or forelimb that runs from the shoulder to the elbow.

Anatomically, it connects the scapula and the radius, and consists of the following three sections:

• Upper extremity of humerus - consisting of a rounded head, a narrow neck, and two short processes, or "tuberosities".
• Body of humerus - cylindrical in its upper portion, and more prismatic below.
• Lower extremity of humerus - consisting of a faceted condyle that articulates with the radius.

[edit] Muscles attached to the humerus

• The deltoid originates on the lateral third of the clavicle, acromion and the spine of the scapula, it is inserted on the deltoid tuberosity of the humerus and has several actions including abduction, extension, and rotation of the shoulder. The supraspinatus also originates on the spine of the scapula, inserts on the greater tubercle of the humerus, and assists in abduction of the shoulder.

• The pectoralis major, teres major, and latissimus dorsi insert at the intertubercular groove of the humerus. They work to adduct and medially, or internally, rotate the humerus.

• The infraspinatus and teres minor insert on the greater tubercle, and subscapularis inserts on the lesser tubercle of the humerus. They all work to laterally, or externally, rotate the humerus. (They are three of the four rotator cuff muscles, the fourth being the supraspinatus, mentioned above).

• The biceps brachii, brachialis, coracobrachialis, and brachioradialis (which attaches distally) act to flex the elbow. The biceps, however, does not attach to the humerus.

• The triceps brachii and anconeus extend the elbow, and attach to the posterior side of the humerus.

[edit] Articulations

• Proximally,the head of the humerus articulates with the glenoid fossa of the scapula.

• Distally, the capitulum of the humerus articulates with the head of the radius, and the trochlea of the humerus articulates with the olecranon process of the ulna.

[edit] Nerves

The most common type of shoulder dislocation is an anterior or inferior dislocation of the humerus of the glenohumeral joint. This dislocation has the potential to injure the axillary nerve or axillary artery. Signs and symptoms of this dislocation include a loss of the normal shoulder contour and a palpable depression under the acromion.

The radial nerve follows the humerus closely. At the midshaft of the humerus, the radial nerve travels from the posterior to the anterior aspect of the bone in the spiral groove. A fracture of the humerus in this region can result in radial nerve injury.

The ulnar nerve at the distal end of the humerus near the elbow is sometimes referred to in popular culture as 'the funny bone'. Striking this nerve can cause a tingling sensation ("funny" feeling), and sometimes a significant amount of pain.

[edit] In other animals

Primitive fossil amphibians had little, if any, shaft connecting the upper and lower extremities, making their limbs very short. In most living vertebrates, however, the humerus has an approximately similar form to that of humans. In many reptiles, and some primitive mammals, the lower extremity includes a large foramen, or opening, into which nerves and blood vessels pass.^[1]

[edit] Additional images

Diagram of the human shoulder joint	Human arm bones diagram	Humerus (right) - anterior view	Humerus (right) - posterior view
Left humerus. Anterior view.	Left humerus. Posterior view.	The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula.	Cross-section through the middle of upper arm.
The Supinator.

[edit] References

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.