Triceps brachii

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Description

The triceps brachii is a large, thick muscle on the dorsal part of the upper arm. It often appears as the shape of a horseshoe on the posterior aspect of the arm. The main function of the triceps is the extension of the elbow joint.

The Triceps brachii gets its name with tri referring to "three" muscle heads or points of origin (with Brachii referring to the arm). These include the: Medial head; Lateral head; Long head

Image 1: Triceps brachii muscle: Long head red; Lateral head yellow; Medial head green

Triceps brachii -Muscles

Long head

• Origin: infraglenoid tubercle of the scapula
• Insertion: Posterior surface of the olecranon process of the ulna, capsule of the elbow joint and antebrachial fascia.
• Action: Because it attaches to the scapula, the long head not only extends the elbow but will also have a small action on the glenohumeral joint. With the arm adducted, the triceps muscle acts to hold the head of the humerus in the glenoid cavity. This action helps prevent any displacement of the humerus. The long head also assists with the extension and adduction of the arm at the shoulder joint. The lateral head is also active during extension of the forearm at the elbow joint when the forearm is supinated or pronated.
• Innervation: radial nerve

Image 2: Long and Lateral head triceps

Lateral Head

• Origin: posterior aspect of the humerus, superior to the radial groove
• Insertion: Posterior surface of the olecranon process of the ulna, capsule of the elbow joint and antebrachial fascia.
• Action: This head is considered to be the strongest head of the three. It is active during extension of the forearm at the elbow joint when the forearm is supinated or pronated.
• Innervation: radial nerve

Medial head

• Origin: posterior aspect of humerus, inferior to the radial groove
• Insertion: Posterior surface of the olecranon process of the ulna, capsule of the elbow joint and antebrachial fascia.
• Action: As the medial head does not attach to the scapula and therefore has no action on the glenohumeral joint, whether with stabilization or movement. However, the medial head is active during extension of the forearm at the elbow joint when the forearm is supinated or pronated.  
• Innervation: radial nerve

Note: All the three heads of triceps brachii are innervated by the four branches of the radial nerve (C7, C8). However, according to the cadaveric study it is found that the medial head of triceps brachii is innervated by the ulnar nerve.. Some research reveals that the long head of triceps is actually innervated by the axillary nerve.

The muscle is supplied with oxygen and nutrients from the branches of the deep brachial artery.

Muscle Fibre Types

Muscle histology and average innervation ratios estimated from absolute mononeurons (MN) counts shows that the lateral head is used for movements requiring occasional high-intensity force, while the medial head enables more precise, low-force movements.

1. medial head was predominantly formed by small type I muscle fibers and motor units (69 fibers/MN).
2. the lateral head comprised a great quantity of large type IIb fibers and motor units (179 fibers/MN)
3. the long head consisted of a more balanced mixture of fiber types and motor units (99 fibers/MN).

Assessment

Palpation

Palpating the three heads of the triceps includes:

Position of the patient: High sitting position

Position of the therapist: Behind the patient

Palpation of medial head- Firstly, use a landmark to palpate the muscle. In this case, the landmark would be medial epicondyle of the humerus. The examiner will place his/her three fingers just above the medial epicondyle and instruct the patient to extend the elbow pushing downward force on the couch as if to lift himself or herself up. Finally palpate the medial head.

Palpation of long head- Palpate from medial condyle of the humerus up to the axilla posteriorly would be the area for long head of triceps. Just beneath the axilla posteriorly, the examiner will place his/her three fingers & instruct the patient to extend the elbow pushing downward. Finally, palpate the long head of the triceps.

Palpation of lateral head- In order to palpate for the lateral head, place three fingers to the postero-lateral side in the middle of the shaft of the humerus & instruct the patient to extend the elbow.

Anconeus- To palpate the anconeus, the landmark would be lateral condyle of the humerus to the proximal ulna & instruct the patient to extend the elbow.