What is the structure and function of the pectoralis muscle including pectoralis major and minor
The anterior chest wall comprises the pectoral regions. It contains four major muscles that exert a force on the upper limb: the pectoralis major muscle, the pectoralis minor muscle, serratus anterior, and subclavius. Pectoral muscles are the muscles that connect the front of the human chest with the bones of the upper arm, shoulder, and the rib cage.
Pectoralis major muscle is a thick fan-shaped muscle, making the bulk of chest muscle. The purpose is to flex, extend, and rotate the humerus, the long bone of the upper arm. Pectoralis minor muscle is a thin, triangular muscle located beneath the pectoralis major muscle which is attached to the ribs and serves to stabilize the scapula - the large bone of the shoulder. The pectoral fascia is a thin layer of tissue over the pectoralis major muscle, that extends towards the latissimus dorsi muscle on the back. Along with pectoralis major and minor, the subclavius muscle forms the axilla or armpit and the serratus anterior is on the front of the chest and moves the scapula forward around the torso for example while throwing a punch. These are the muscles of the pectoral region.
Pectoralis Major and Minor Muscles
Pectoralis Major Muscle
The pectoralis major muscle is the larger and more superficial muscle. Pectoralis major originates from distinct places. It originates at the clavicle or the collarbone, the sternum, the ribs and a tendinous extension of the external oblique abdominal muscle. It extends across the upper part of the chest and is attached to a ridge at the rear of the humerus i.e. the bone of the upper arm. From these origins, the fibres converge to the pectoralis major insertion. The ones arising from the clavicle pass obliquely downward and laterally outward and are separated from the rest by an interval. Those originating from the lower part of the sternum and the cartilages of true ribs run upward and laterally and the middle fibres pass horizontally. The pectoralis major is shown in the given diagram below:
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The pectoralis major muscle ends in a flat tendon which is inserted into the lateral lip of the bicipital groove of the humerus.
The pectoralis major function is to move the shoulder joint. The actions that are facilitated by pectoralis major include, flexion, adduction or depression, and rotation. These functions allow us to do activities such as lifting a child, flapping the arms, and arm-wrestling respectively. These are helpful when the raised arms are fixed for example in climbing where it aids the latissimus dorsi and teres major muscles in pulling. Importantly, the pectoralis major muscle keeps the arm attached to the trunk body.
The pectoralis major muscle can be targeted by various exercises such as plating and bench press, etc. Although these exercises are important for pectoralis major activation, it is necessary to be careful while following the routine of the exercises so that there is no tear and no damage to the muscles.
Pectoralis Minor Muscle
The pectoralis minor muscle lies under the pectoralis major. It starts from the middle of the ribs i.e. the upper and outer surfaces of the third, fourth, and fifth ribs, also from near their cartilages and from the aponeuroses covering the intercostalis and inserts into or attaching to the scapula or the shoulder blade. The given below diagram shows the origins and insertions of pectoralis minor muscle:
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The pectoralis minor helps in moving the shoulder forward and downward which physiologically opposes the trapezius muscle. The pectoralis minor pushes down the point of the shoulder, which draws the scapula superior towards the thorax and throws its inferior angle posteriorly.
Thus, the pectoral region houses important pectoralis muscle - the pectoralis major muscle and the pectoralis minor muscle that not only provide locomotive flexibility to the shoulder and the arms but also keep them attached to the main body and with the ribs. This pectoralis is known as ‘pecs’ or ‘chest muscles’ as well. Most of the chest building exercises are centred around the activation of the pectoral muscles.
FAQs on Pectoralis Muscle Anatomy and Role in the Chest
1. What is the pectoralis muscle?
The pectoralis muscle is a large chest muscle that connects the upper limb to the front of the chest wall and enables shoulder movement. It mainly includes two muscles: pectoralis major and pectoralis minor.
- Pectoralis major: Large, fan-shaped muscle responsible for arm movements.
- Pectoralis minor: Smaller, triangular muscle located beneath pectoralis major.
2. What is the function of the pectoralis major?
The pectoralis major functions to flex, adduct, and medially rotate the arm at the shoulder joint. Its main actions include:
- Flexion: Raising the arm forward.
- Adduction: Bringing the arm toward the body.
- Medial rotation: Rotating the arm inward.
3. What is the function of the pectoralis minor?
The pectoralis minor stabilizes and moves the scapula (shoulder blade). Its key functions are:
- Pulling the scapula forward and downward.
- Stabilizing the scapula against the chest wall.
- Assisting in forced inspiration by elevating the ribs when the scapula is fixed.
4. Where is the pectoralis muscle located?
The pectoralis muscles are located in the anterior (front) part of the chest wall. Specifically:
- Pectoralis major covers the upper chest, extending from the clavicle and sternum to the humerus.
- Pectoralis minor lies beneath pectoralis major, attaching from the ribs to the scapula.
5. What is the difference between pectoralis major and pectoralis minor?
The main difference between pectoralis major and pectoralis minor is their size, location, and function.
- Pectoralis major: Larger, superficial muscle that moves the arm.
- Pectoralis minor: Smaller, deeper muscle that stabilizes the scapula.
6. What type of muscle is the pectoralis muscle?
The pectoralis muscle is a type of skeletal muscle that is under voluntary control. Skeletal muscles:
- Are attached to bones via tendons.
- Contain striated muscle fibers.
- Are controlled by the somatic nervous system.
7. What is the origin and insertion of the pectoralis major?
The pectoralis major originates from the clavicle, sternum, and upper ribs and inserts into the humerus. Specifically:
- Origin: Medial clavicle, sternum, and costal cartilages of ribs 1–6.
- Insertion: Lateral lip of the intertubercular sulcus of the humerus.
8. How is the pectoralis muscle innervated?
The pectoralis muscles are innervated by the medial and lateral pectoral nerves from the brachial plexus.
- Lateral pectoral nerve: Primarily supplies pectoralis major.
- Medial pectoral nerve: Supplies both pectoralis major and minor.
9. What movements use the pectoralis muscles?
The pectoralis muscles are used in pushing, lifting, and hugging movements of the arms. Common actions include:
- Push-ups and bench presses.
- Throwing or punching.
- Bringing the arms across the chest (horizontal adduction).
10. Why are the pectoralis muscles important in respiration?
The pectoralis minor assists in forced inspiration by elevating the ribs when the scapula is fixed. During deep or labored breathing:
- The scapula is stabilized.
- The muscle pulls the ribs upward.
- This increases thoracic cavity volume.
