General classification of chest muscles
Anatomically, the muscles of the chest wall (mm. thoracis) are divided into two large groups depending on their origin and functions:
- Superficial muscles. These include the pectoralis major and minor, subclavius, and serratus anterior muscles. Evolutionarily, they developed alongside the arms and migrated to the trunk, thus controlling the shoulder girdle.
- Deep (intrinsic) muscles. Include the external, internal, and innermost intercostal, subcostal, transversus thoracis, and levatores costarum muscles. These are the true muscles of the thoracic wall, whose main function is to facilitate breathing.
Pectoralis major muscle
The pectoralis major muscle (m. pectoralis major) is a powerful fan-shaped muscle occupying a significant portion of the anterior thoracic wall.
Depending on its points of origin, it has three parts:
- Pars clavicularis (clavicular part) — originates from the medial half of the clavicle.
- Pars sternocostalis (sternocostal part) — originates from the anterior surface of the sternum and the cartilages of ribs II–VII.
- Pars abdominalis (abdominal part) — originates from the anterior wall of the sheath of the rectus abdominis muscle (m. rectus abdominis).
Insertion: The muscle fascicles converge laterally and attach to the crest of the greater tubercle of the humerus. An interesting feature: the tendon forms a double U-shaped fold, with the upper muscle fascicles inserting more distally than the lower ones.
Function: Provides adduction, internal rotation (pronation), and flexion of the arm. If the arms are fixed, the muscle pulls the ribs upward, assisting in deep inspiration.
Innervation and blood supply: Controlled by the medial and lateral pectoral nerves (nn. pectorales medialis et lateralis, segments C5–Th1). Supplied by the pectoral branch of the thoracoacromial artery, lateral and superior thoracic arteries, and anterior intercostal branches.
Pectoralis minor muscle
The pectoralis minor muscle (m. pectoralis minor) is triangular in shape and lies deep to the pectoralis major muscle.
- Origin: Arises by individual slips from the anterior ends and cartilages of ribs II–V.
- Insertion: The tendon attaches to the coracoid process of the scapula.
- Function: The main action is to pull the scapula inferiorly and anteriorly. Like the pectoralis major, when the scapula is fixed, the muscle elevates the ribs, acting as an accessory respiratory muscle for inspiration.
- Innervation and blood supply: Innervated by the medial pectoral nerve (C7–Th1), with occasional contribution from the lateral pectoral nerve. It receives blood supply from the thoracoacromial and lateral thoracic arteries.
Subclavius muscle
The subclavius muscle (m. subclavius) is a small muscular band located between the clavicle and the first rib.
- Origin: Arises from the bony part of rib I near its cartilage.
- Insertion: Attaches to the inferior surface of the middle third of the clavicle (in the subclavian groove — sulcus m. subclavii).
- Function: Pulls the clavicle inferiorly and medially. The main biomechanical role is stabilization of the sternoclavicular joint during movements of the shoulder girdle.
- Innervation and blood supply: Innervated by the subclavicular nerve (n. subclavius, segments C5–C6). Supplied by branches of the thoracoacromial and superior thoracic arteries.
Briefly: answers to topical questions
Where does the serratus anterior muscle originate and insert?
The serratus anterior muscle (m. serratus anterior) originates from ribs I–IX by 8–9 slips and inserts into the scapula.
- Origin — by 8–9 slips from ribs I–IX (maximum development of the muscle is observed in the region of the inferior angle of the scapula).
- Insertion — medial border and inferior angle of the scapula on the anterior surface.
What function does the serratus anterior muscle perform?
The serratus anterior muscle (m. serratus anterior) provides movements of the scapula and participates in respiration.
- Scapular movement — pulls the scapula forward and laterally, rotates it outwardly and upwardly, which allows raising the arm above the horizontal.
- Fixation — stabilizes and fixes the scapula to the chest wall when raising the arm.
- Respiration — the lower fascicles of the muscle act as a powerful inspiratory stabilizer.
What innervates the serratus anterior muscle?
The serratus anterior muscle (m. serratus anterior) is innervated by the long thoracic nerve (n. thoracicus longus) from segments C5–C7. The nerve runs along the superficial surface of the serratus anterior muscle.
Which arteries supply blood to all superficial chest muscles?
The superficial chest muscles are supplied by the following arteries:
- Pectoralis major muscle (m. pectoralis major) — pectoral branches of a. thoracoacromialis, a. thoracica lateralis, a. thoracica superior, anterior intercostal arteries.
- Pectoralis minor muscle (m. pectoralis minor) — a. thoracoacromialis, a. thoracica lateralis.
- Subclavius muscle (m. subclavius) — a. thoracoacromialis, a. thoracica superior.
- Serratus anterior muscle (m. serratus anterior) — a. thoracodorsalis, a. thoracica lateralis, anterior intercostal arteries.
To easily remember the origin and insertion points of the pectoralis minor muscle, use the association: 'The MINOR pectoral starts with the SMALL number 2 (ribs II-V) and extends to the BEAK of the scapula (coracoid process)'.
Class and exam questions
How do the superficial chest muscles participate in the act of respiration?
When the upper extremity is fixed (e.g., when a person leans hands on a table during shortness of breath), the pectoralis major and minor change their fulcrum and begin to pull the ribs upward, expanding the chest for inspiration.
Where does the abdominal part of the pectoralis major muscle originate?
The abdominal part (pars abdominalis) originates from the anterior wall of the sheath of the rectus abdominis muscle (m. rectus abdominis).
Which muscle stabilizes the sternoclavicular joint?
This function is performed by the subclavius muscle (m. subclavius), which pulls the clavicle inferiorly and medially, pressing it firmly against the sternum.
What else to study on this topic
- Anatomy of the serratus anterior muscle (m. serratus anterior)
- Deep (intrinsic) muscles of the thoracic wall
- External and internal intercostal muscles
- Transversus thoracis and subcostal muscles
- Topography of the thoracoacromial artery
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