Arm Muscles

The muscles in the upper arms are located between the shoulder and elbow joints and can be categorized into anterior and posterior compartments.

Anterior Compartment

The following muscles can be found in the anterior compartment of the upper arm:

  1. Biceps Brachii - This muscle has two heads and as it’s tendon enters the region of the forearm, the bicipital aponeurosis forms the roof of the cubital fossa and blends with the deep fascia of the anterior forearm.

    • This muscle has different points of origin for its two heads:

      • Long head: this originates from the supraglenoid tubercle of the scapula

      • Short head: this originates from the coracoid process of the scapula

    • Both heads attach to the radial tuberosity (distally) of the humerus and fascia of the forearm.

    • This muscle acts to supinate the forearm and flex the arm at the shoulder and elbow joints.

    • This muscle is innervated by the musculocutaneous nerve.

  2. Coracobrachialis

    • This muscle originates from the coracoid process of the scapula and passes through the axilla to attach to the medial side of the shaft of the humerus.

    • This muscle acts to flex the arms at the shoulder joint and is a weak adductor.

    • This muscle is innervated by the musculocutaneous nerve.

  3. Brachialis - forms the floor of the cubital fossa.

    • This muscle originates from the medial and lateral surfaces of the shaft of the humerus and inserts into the ulnar tuberosity.

    • This muscle acts to flex the arm at the elbow joint.

    • This muscle is innervated by the musculoskeletal nerve.

Posterior Compartment

The following muscle can be found in the posterior compartment of the arm:

  1. Triceps Brachii - This muscle has three heads, the medial of which lies the deepest.

    • This muscle has different points of origin for its three heads:

      • Long head: this originates from the infraglenoid tubercle

      • Lateral head: this originates from the humerus, superior to the radial groove

      • Medial head: this originates from the humerus, inferior to the radial groove

    • All three heads of this muscle converge into one tendon and insert into the olecranon of the ulna.

    • This muscle acts to extend the arm at the elbow joint.

    • The muscle is innervated by the radial nerve.

Clinical Notes:

  1. The musculocutaneous nerve pierces the coracobrachialis muscle.

  2. Shoulder pain or inflammation may be experienced over time due to the position of the tendon of the long head of the biceps brachii as it is located in the intertubercular sulcus between the greater and lesser tuberosities of the humerus.

  3. Biceps brachii tendon reflex can be tested by tapping on the biceps tendon at the cubital fossa to ensure the integrity of the C5 and C6 spinal segments as well as the musculocutaneous nerve.

  4. Triceps brachii tendon reflex can be tested by tapping on the triceps tendon at the olecranon to ensure the integrity of the C6 to C8 spinal segments as well as the radial nerve.