Bones of the Arm Diagram and their Features

The bones of the arm are a complex of many bones, each with a unique function. To understand how the bones of the arm and hand function, we first need to understand their structure and location in the human body. The anatomy of the bones in the arm in humans is represented in the labeled diagram below.

Humerus

The humerus is the longest bone of the upper arm that extends from the shoulder to the elbow. The anatomy of humerus is mentioned below:

1. Proximal End: The proximal end of the humerus is divided into a rounded head that articulates with the glenoid cavity of the scapula, forming the ball and socket shoulder joint (glenohumeral joint). It also has two tubercles (bony projections) for muscle attachment and the neck.
2. Shaft: The shaft is the long body of the bone. It has the deltoid tuberosity, a rough, V-shaped area where the deltoid muscle attaches. It also has a radial groove, the site of radial nerve innervation.
3. Distal End: The distal end features the capitulum, a rounded knob-like structure that articulates with the head of the radius (radiocapitellar joint). It also has the trochlea, a spool-shaped structure articulating with the ulna (humeroulnar joint). Together, these two joints make up the elbow joint. Medial and lateral epicondyles (bony projections), fossae (depressions), and ridges are on either side of the distal end. They serve as attachment points for various muscles and ligaments, contributing to the stability and movement of the elbow joint.

Radius and Ulna

The radius and ulna are the forearm bones. The different structures associated with each of these bones are described below.

Radius

This bone is located on the thumb side of the forearm. Radius bone parts are:

• Proximal end: The proximal end has a rounded head that articulates with the humerus capitulum and the ulna’s radial notch.
• Neck: It is located just below the head and is a common fracture site.
• Shaft: The main body of the bone with the radial tuberosity is the site of attachment for the biceps brachii muscle.
• Distal End: The distal end articulates with the wrist bone with the styloid process.

Ulna

The ulna is located on the pinky side of the forearm. It is longer than the radius and runs parallel to it. The ulna bone anatomy is:

• Proximal end: The proximal end of the ulna has many bony projections with unique functions. These include the olecranon process, which forms the prominent point of the elbow, and the coronoid process, along with the olecranon, which articulates with the humerus. It has two notches, namely, the trochlear notch with the humerus’s trochlea, forming the elbow’s hinge joint and the radial notch articulating with the head of the radius.
• Shaft: This is the attachment site for muscles such as the flexor and pronator muscles.
• Distal end: Like the radius, the distal has the styloid process that forms the wrist joint.

The Bones of the Arm are the humerus, radius, and ulna together with the muscles, ligaments, and tendons, these bones allow for mobility and offer structural support. The arm’s three bones are hard, and more than 80% of its bulk is compact bone.

Spongy bone makes up less than 20% of the arm’s mass, particularly at the tips. The bones of the arm and hand are responsible for all the functions we perform with our hands, like writing, lifting, grabbing, throwing, etc. In this article, we will discuss various bones of the arms, their function, and diagram.