Pectoralis Minor: Origin, Insertion, Nerve, Action & Posture

The Pectoralis Minor is a small, triangular muscle located deep to the Pectoralis Major in the anterior chest wall. Despite its size, it is a major culprit in poor posture ("Rounded Shoulders") and can compress vital nerves and arteries supplying the arm.

[Image of External Oblique muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Anterior surfaces of Ribs 3, 4, and 5 (near the costal cartilage).
Insertion (Distal)	Medial border and superior surface of the Coracoid Process of the Scapula.
Nerve Supply	Medial Pectoral Nerve (C8, T1). (Note: It is often pierced by the medial pectoral nerve, and sometimes receives branches from the lateral pectoral nerve via the communicating loop).
Blood Supply	Pectoral branch of the Thoracoacromial Artery.
Primary Actions	Scapular Protraction: Pulls the shoulder blade forward (abduction). Scapular Depression: Pulls the shoulder blade down. Anterior Tilt: Tips the scapula forward (inferior angle lifts off). Inspiration: Elevates ribs when the scapula is fixed (Accessory breathing muscle).

Deep Dive: The Gateway to the Axilla

The Pectoralis Minor acts as an anatomical landmark and a "bridge" for neurovascular structures.

1. The Neurovascular Gatekeeper

The muscle forms a bridge over the axillary artery, vein, and brachial plexus cords.
Anatomists divide the Axillary Artery into three parts based on its relationship to the Pectoralis Minor:
• Part 1: Proximal (medial) to the muscle.
• Part 2: Posterior (deep) to the muscle.
• Part 3: Distal (lateral) to the muscle.

2. The Coracoid Anchor

It anchors the scapula to the front of the rib cage. Because it attaches to the Coracoid Process, when it tightens, it pulls the top of the scapula forward. This creates the "tipped" scapula seen in poor posture, where the bottom of the shoulder blade sticks out (winging) while the top rounds forward.

Physio Corner: Clinical Relevance

💪 Functional Fact: While Pectoralis Major moves the arm, Pectoralis Minor moves the scapula. It is essential for pushing movements (like a push-up or punching) where the scapula must wrap around the rib cage (protraction).

Palpation

To feel the Pectoralis Minor, you must go under the Pectoralis Major.
1. Have the patient lie supine.
2. Locate the Coracoid Process (bony knob below the lateral clavicle).
3. Slide your fingers inferiorly and medially from the coracoid, pressing gently through the Pectoralis Major bulk.
4. Ask the patient to lift their shoulder off the table (anterior tilt) without shrugging. You will feel the resistance of the Pec Minor.

⚠️ Clinical Pathology: Pectoralis Minor Syndrome (TOS)
Tightness in this muscle can compress the neurovascular bundle (Brachial Plexus and Axillary vessels) against the rib cage. This is a form of Thoracic Outlet Syndrome (TOS). Symptoms include numbness in the hand (especially pinky/ring finger) and a weak pulse when the arm is raised.

Manual Muscle Testing (MMT)

We test Scapular Anterior Tilt/Depression to isolate it from the Serratus Anterior.

Testing Tip: Ensure the patient does not use the arm to push. The motion comes purely from the shoulder blade lifting off the table.

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Gravity)	Position: Supine. Arm at side. Action: Patient lifts the shoulder forward off the table (anterior tilt/protraction), essentially thrusting the shoulder toward the ceiling. Resistance: Therapist applies downward pressure on the anterior aspect of the shoulder (coracoid region), pushing it back into the table. Grade 3: Completes range against gravity. Grade 4/5: Holds against resistance.
Grade 0, 1 (Palpation)	Action: Palpate just inferior to the coracoid process. Cue: "Try to lift your shoulder tip off the table." Grade 1: Deep contraction felt. Grade 0: No activity.

Frequently Asked Questions

Does it act on the humerus?

No. It attaches to the Scapula (Coracoid Process). It does not cross the shoulder joint (glenohumeral joint), so it cannot move the humerus directly. It moves the scapula, which indirectly affects shoulder position.

How do I stretch the Pec Minor?

The "Doorway Stretch" with arms high (elbows above shoulders) targets the Pec Minor. If the elbows are low, you stretch the Pec Major (Clavicular head).

Why is it an accessory breathing muscle?

If you stabilize your shoulder blades (e.g., by placing hands on knees after a run), the Pec Minor reverses its action. Instead of pulling the scapula down, it pulls the Ribs (3-5) Up, helping to expand the chest for air.

Test Your Knowledge: Pectoralis Minor Quiz

1. Where does the Pectoralis Minor insert?

2. Which nerve supplies the Pectoralis Minor?

3. What is a primary action of the Pectoralis Minor?

4. The Pectoralis Minor divides which artery into three parts?

5. Tightness of the Pectoralis Minor contributes to which syndrome?

6. Where does the Pectoralis Minor originate?

7. Does the Pectoralis Minor lie superficial or deep to the Pectoralis Major?

8. Which scapular movement creates "Anterior Tilt"?

9. To stretch the Pec Minor specifically, elbows should be placed:

10. Which other muscle attaches to the Coracoid Process?

References

• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2018). Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer.
• Standring, S. (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Elsevier.
• Kendall, F. P. (2005). Muscles: Testing and Function, with Posture and Pain. 5th ed. Lippincott Williams & Wilkins.