Lab 4 - Module 1 - Extensor Compartments of the Arm and Forearm: Page 2 of 9
Extensor Arm:
| • The posterior compartment of the arm is also known as the extensor compartment of the arm. There are two muscles that reside in the posterior compartment of the arm. The only one of significance is the triceps brachii muscle which covers the entire posterior aspect of the arm. |
| Begin a posterior view of the bones of the upper extremities. |
| Add the Anconeus muscle. Is the small muscle that is associated with the triceps at the elbow. |
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Origin - the lateral epicondyle of the humerus. Insertion - the lateral side of the olecranon process and an adjacent part of the body of the ulna. Innervation - the Radial nerve. Action - There is much debate over the true function of this small muscle. Some anatomists argue it aids in elbow extension and others say it simply aids in the stability of the lateral aspect of the elbow joint. There is also speculation that it helps control valgus force at the elbow during extension movements. One can also speculate it may help to pull the joint capsule (which is redundant) out of the joint during flexion so as to not pinch the capsule in the joint. Blood supply - the Profunda Brachii artery. |
| • The Triceps Brachii is the muscle that covers the entire posterior aspect of the arm. The triceps, as the name implies, has three heads of origin; lateral head, long head, and medial head. |
| Add the Lateral Head of the Triceps Brachii muscle. |
| Origin of the lateral head - from the posterior surface of the humerus lateral to the radial groove and from the intermuscular septum. The lateral head and the long head merge to form the superficial portion of the triceps brachii muscle. |
| Add the Medial Head of the Triceps Brachii muscle. |
| Origin of the medial head - from the entire posterior surface of the humerus, inferior to the radial groove and from the medial and lateral intermuscular septum, inferior from where the radial nerve passes through the septum. It merges with the deep aspects of the long and lateral heads. |
| Add the Long Head of the Triceps Brachii muscle. |
| Origin of the long head - is a strong tendon on the infraglenoid tubercle of the scapula. It passes downwards between teres minor and teres major and separates the quadrangular space from the triangular space. This is the only part of the triceps to cross the shoulder joint. |
| Add the The entire Triceps Brachii muscle. |
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Insertion - a strong uniformed tendon which inserts on the olecranon process of the ulna.
Innervation - radial nerve. Action - functions as a powerful elbow extensor and may contribute, weakly, to shoulder extension. Blood supply - Profunda Brachii artery |