Triceps Brachii
The triceps brachii is a three-headed muscle located on the posterior compartment of the upper arm. It is the only muscle in the posterior arm and is the primary extensor of the elbow joint.
Origin, Insertion, Action, Innervation
OOrigin
Long head: Infraglenoid tubercle of scapula. Lateral head: Posterior humerus (above radial groove). Medial head: Posterior humerus (below radial groove).
IInsertion
Olecranon process of ulna
AAction
- • Extension of the elbow joint (all three heads)
- • Extension of the shoulder joint (long head only)
- • Adduction of the arm (long head assists)
NInnervation
Radial nerve (C6, C7, C8)
Blood Supply
Deep brachial artery (profunda brachii)
Clinical Relevance
The radial nerve runs in the radial groove between the lateral and medial heads, making it vulnerable in humeral shaft fractures. Triceps reflex tests C7 nerve root. Complete radial nerve palsy causes 'wrist drop' and weak elbow extension.
Palpation
Palpate on the posterior arm. Have the patient extend the elbow against resistance to make the muscle prominent. The long head can be felt near the axilla.
Study Tips
- ✓Three heads = three origins, one insertion (olecranon)
- ✓Only the long head crosses the shoulder joint
- ✓Radial nerve runs through radial groove - vulnerable in humerus fractures
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Common questions about the triceps brachii
All three heads of the triceps brachii converge to insert on the olecranon process of the ulna via a common tendon.
The triceps brachii is innervated by the radial nerve, carrying fibers from the C6, C7, and C8 nerve roots.
Only the long head of the triceps crosses the shoulder joint, originating from the infraglenoid tubercle of the scapula. This allows it to assist in shoulder extension and adduction.
The radial nerve runs in the radial groove of the humerus between the lateral and medial heads of the triceps. Humeral shaft fractures can damage this nerve, causing weakness in wrist and finger extension ('wrist drop').