Triceps Brachii Muscle Anatomy

The triceps brachii is a large fusiform muscle in the posterior compartment of the arm. The triceps is the main extensor of the forearm.

Triceps Brachii Muscle Anatomy

As its name indicates, the triceps brachii has three heads: long, lateral, and medial.

Origin

The long head of triceps muscle arises from the infraglenoid tubercle of scapula, the lateral head arises from the posterior surface of humerus, superior to radial groove while the medial head arises from the posterior surface of humerus, inferior to radial groove.

Insertion

The three heads unite altogether forming the triceps muscle tendon that inserts on the proximal end of olecranon process of ulna and fascia of forearm.

See Also: Elbow Anatomy

Innervation

It’s innervated by the radial nerve (C6, C7 and C8) (C6, C7, C8).

Blood Supply

Its blood supply comes from branches of deep brachial artery.

Action

Because its long head crosses the glenohumeral joint, the triceps helps stabilize the adducted glenohumeral joint by serving as a shunt muscle, resisting inferior displacement of the head of the humerus. The long head also aids in extension and adduction of the arm, but it is the least active head.

The medial head is the workhorse of forearm extension, active at all speeds and in the presence or absence of resistance.

The lateral head is the strongest but is it recruited into activity primarily against resistance. Pronation and supination of the forearm do not affect triceps operation. Just proximal to the distal attachment of the triceps is a friction-reducing subtendinous olecranon bursa, between the triceps tendon and the olecranon.

See Also: Forearm Muscles Anatomy & Function

Triceps Muscle Injury

Ruptures of the triceps muscle are rare and typically only occur in anabolic steroid users. Distal triceps ruptures are also relatively uncommon. The injury typically occurs due to either a fall on an outstretched hand or a direct blow to the triceps tendon. Surgical consideration for a partial rupture is controversial, but it is necessary for a complete rupture.

To test the triceps brachii (or to determine the level of a radial nerve lesion), the arm is abducted 90° and then the flexed forearm is extended against resistance provided by the examiner. If acting normally, the triceps can be seen and palpated. Its strength should be comparable with the contralateral muscle, given consideration for lateral dominance (right or left handedness).

The triceps brachii reflex tests spinal nerves C6 and C7, predominately C7. The reflex is tested by abducting the patient’s shoulder and elbow to 90 degrees. Then the triceps tendon is tapped using a reflex hammer just proximal to the olecranon.

References & More

1. Clinically Oriented Anatomy – 8th Edition
2. Tiwana MS, Sinkler MA, Bordoni B. Anatomy, Shoulder and Upper Limb, Triceps Muscle. [Updated 2023 Aug 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK536996/