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Humerus

life science Maturity 11-13 Next article →

The humerus is a long bone located in the upper arm.

Humerus ant (mirroed)
Humerus ant (mirroed)

It spans the distance from the shoulder to the elbow. This bone serves as a vital bridge in the arm's structure. It connects the scapula, which is the shoulder blade, to the two lower arm bones. These lower bones are the radius and the ulna.

Humerus-Head
Humerus-Head

The humerus is essential for movement and stability. It provides many attachment points for the muscles that move the arm. Understanding its complex shape helps us see how the human arm functions.

The bone is divided into three distinct sections. The first is the proximal extremity, or the upper end.

Neck-of-Humerus
Neck-of-Humerus

The second section is the shaft, which forms the long middle part of the bone. The third section is the distal extremity, located at the bottom near the elbow.

Capitulum-and-trochlea
Capitulum-and-trochlea

Each section has specific shapes and features. These features allow the bone to interact with muscles, nerves, and other bones. The way these parts fit together determines how we can swing or lift our arms.

At the top, the proximal extremity begins with a large, rounded head. This head is nearly hemispherical in shape. It directs upward and inward to meet the glenoid cavity of the scapula. This connection creates the glenohumeral joint, or the shoulder joint.

Humerus-Head
Humerus-Head

Below the head is the anatomical neck. This is a narrow groove that separates the head from the tubercles. The anatomical neck provides an attachment site for the articular capsule. It also contains many small holes called vascular foramens for blood vessels. Fractures at the anatomical neck are quite rare.

Just below the tubercles lies the surgical neck. This area is a narrow constriction of the bone. It is called the surgical neck because it is a frequent site for fractures.

Neck-of-Humerus
Neck-of-Humerus

This part of the bone is very important for surgeons to study. The surgical neck makes contact with the axillary nerve. It also sits near the posterior humeral circumflex artery. Because of its location and shape, it is more vulnerable to injury than the anatomical neck.

The upper end also features two bony projections called tubercles. The greater tubercle is a large projection located on the outer side.

Greater-Tubercle-of-Right-Humerus
Greater-Tubercle-of-Right-Humerus

It serves as an attachment point for three muscles: the supraspinatus, infraspinatus, and teres minor. The lesser tubercle is a smaller projection located toward the front.

Lesser-Tubercle-of-Right-Humerus
Lesser-Tubercle-of-Right-Humerus

It provides an insertion point for the subscapularis muscle. Between these two tubercles is the bicipital groove.

Bicipital-groove
Bicipital-groove

This deep groove holds the long tendon of the biceps brachii muscle. It also carries a branch of the anterior humeral circumflex artery.

The shaft of the humerus is the long, middle portion. It is shaped like a cylinder or a triangle. The shaft has three main surfaces: the anterolateral, the anteromedial, and the posterior surface.

Anterior-view-of-the-humerus-showing-borders-and-surfaces
Anterior-view-of-the-humerus-showing-borders-and-surfaces

On the lateral side, a rough bump called the deltoid tuberosity exists. This is where the deltoid muscle attaches.

Deltoid-Tuberosity
Deltoid-Tuberosity

On the back of the shaft is the radial sulcus, or spiral groove.

Radial-groove-continuing-as-lateral-border-of-shaft
Radial-groove-continuing-as-lateral-border-of-shaft

This groove allows the radial nerve and deep vessels to pass through. Additionally, a small hole called the nutrient foramen allows nutrient arteries to enter the bone.

The distal extremity is the lower end of the bone near the elbow. This section is somewhat flattened and curves slightly forward.

It features two bony bumps called the medial and lateral epicondyles. The articular surface here is split into two parts. One part is the capitulum, which is a smooth, rounded knob.

Capitulum-and-trochlea
Capitulum-and-trochlea

The other part is the trochlea.

Capitulum-and-trochlea
Capitulum-and-trochlea

The bone also contains three hollow spaces called fossae. These include the radial fossa, the coronoid fossa, and the olecranon fossa.

Olecranon-fossa
Olecranon-fossa

These depressions allow the bones of the forearm to fit into the humerus during movement.

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🖼️ Images & Media (28)
File:Humerus-Head.gif
Humerus-Head.gif
File:Neck-of-Humerus.jpg
Neck-of-Humerus.jpg
File:Greater-Tubercle-of-Right-Humerus.jpg
Greater-Tubercle-of-Right-Humerus.jpg
File:Attachments-of-greater-tubercle.jpg
Attachments-of-greater-tubercle.jpg
File:Lesser-Tubercle-of-Right-Humerus.jpg
Lesser-Tubercle-of-Right-Humerus.jpg
File:Insertion-of-subscapularis-muscle.jpg
Insertion-of-subscapularis-muscle.jpg
File:Bicipital-groove.jpg
Bicipital-groove.jpg
File:Anterior-view-of-the-humerus-showing-borders-and-surfaces.jpg
Anterior-view-of-the-humerus-showing-borde...
File:Posterior-view-of-the-humerus-showing-borders-and-surfaces.jpg
Posterior-view-of-the-humerus-showing-bord...
File:Deltoid-Tuberosity.jpg
Deltoid-Tuberosity.jpg
File:Radial-groove-continuing-as-lateral-border-of-shaft.jpg
Radial-groove-continuing-as-lateral-border...
File:Nutrient-Foramen.jpg
Nutrient-Foramen.jpg

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