May 21, 2011

Anatomy Basics: Muscles of the upper arm

Now that I am finding the format I like to follow for the anatomy basics posts I want to revisit the anatomy of the arm to present it a little more clearly. I am looking to for ways approach the anatomy of the human form that assist us in our drawing. Looking at the shapes and location of the muscles is a good place to start.

Today, we will look at a few of the muscles found in the upper arm, including the biceps, triceps, brachialis, and coracobrachialis. We will look at the attachment points of the muscles and how these muscles move the arm. 

Let's begin.

First, let me explain the images. These charts are designed to allow us to see the general shape, placement, and attachment points of individual muscles. The muscles are represented in flat simple shapes with distinct colors to highlight each muscle.  I am not making any distinctions between muscle fiber and tendons right now. They are being lumped together for simplification. 


The biceps brachii is the muscle on the front of the upper arm. This muscle gets the name bicep because it is composed of two heads (bodies of muscle). The biceps brachii is responsible for bending the arm at the elbow bringing the forearm up towards the upper arm (flexion).

The biceps brachii attaches to the scapula, span across the bone of the upper arm (humerus), and end by attaching to the radius (one of the bones in the forearm)   

Origin: The scapula, at the coracoid process and the supraglenoid tubercle
Insertion: Radius at the radial tuberosity and into fascia found on the medial part of the forearm
Action: Flexes of the arm at the elbow

The coracobrachialis is a muscle that is tucked in between the larger biceps and triceps. Though it is not completely obscured by the two.  This muscle moves the arm at the shoulder, bringing the arm up and in towards the body.

The coracobrachialis starts at the scapula on a protrusion of bone called the coracoid process. This band of muscle continues down the upper arm and attaches to the inside of the humerus.

Origin: The scapula at the coracoid process 
Insertion: The middle of the shaft of the humerus on the medial side.
Action: Flexes and adducts the arm at the shoulder 

The brachialis sits on the lower half of the humerus in the upper arm and under the biceps brachii. Working with the biceps this muscle bends the arm at the elbow, bringing the forearm closer to the shoulder.

Origin: The humerus at the middle of the shaft  
Insertion: The upper portion of the ulna, at the coronoid process and ulnar tuberosity 
Action:  Flexes of the arm at the elbow

This last one is a large muscle on the back (posterior side) of the upper arm. The name of this muscle also gives a clue as to how many heads are contained within. The triceps perform the opposite task of the biceps. This muscle extends the arm at the elbow, straightening it out.

The triceps attaches the scapula and to a couple of spots on the back of the humerus. It spans across the back of the humerus down to the elbow and attaches to the top of the ulna.

Origin: The scapula at the infraglenoid tubercle and the posterior of the humerus
Insertion: The ulna at the olecranon process
Action: Extends the arm at the elbow


Reference and Sources

Richer, Paul and Hale, Robert Beverly, Artistic AnatomyWatson-Guptill publications, New York, 1971