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Questions and Answers
What is the primary action of the pectoralis major muscle?
Which nerve supplies the pectoralis minor muscle?
What is the origin of the serratus anterior muscle?
What role does the subclavius muscle play during shoulder joint movement?
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What is the insertion point of the pectoralis minor muscle?
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Which artery pierces the clavipectoral fascia?
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What is the action of the serratus anterior muscle?
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Which of the following describes the origin of the pectoralis major?
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Which trunks are formed by the roots of C5, C6, C7, C8, and T1?
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In which region do the roots and trunks of the brachial plexus lie?
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What is the structure formed by the anterior divisions of the upper and middle trunks?
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Which nerve is primarily associated with the medial cord?
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Which of the following is NOT a muscle of the pectoral region?
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What is described as a pyramidal space between the upper arm and the side of the chest?
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What condition is caused by a lesion of the long thoracic nerve?
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Which nerve is categorized as part of the posterior cord?
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What structure connects the axilla to the neck?
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Which muscles form the posterior wall of the axilla?
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What is the base of the axilla primarily formed by?
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Which structure is not a content of the axilla?
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What bones form the apex of the axilla?
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Which of the following is formed by muscles in the medial wall of the axilla?
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What forms the lateral wall of the axilla?
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What is the primary function of the brachial plexus?
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Study Notes
Pectoralis Major
- Originates from two heads: the clavicular head and the sternocostal head.
- The clavicular head originates from the medial half of the anterior clavicle.
- The sternocostal head originates from the sternum, the upper six costal cartilages, and the aponeurosis of the external oblique muscle.
- Inserts into the lateral lip of the bicipital groove.
- Innervated by the medial and lateral pectoral nerves.
- Function: adduction and medial rotation of the arm.
- The clavicular head assists in flexion of the arm (shoulder).
Pectoralis Minor
- Originates from the 3rd, 4th, and 5th ribs close to their costal cartilages.
- Inserts into the coracoid process.
- Innervated by the medial pectoral nerve.
- Function: depression of the shoulder, draws the ribs upward and outwards during deep inspiration.
Subclavius
- Originates from the 1st rib at its costal cartilage.
- Inserts into the subclavian groove in the middle 1/3 of the inferior surface of the clavicle.
- Innervated by the nerve to subclavius from the upper trunk of the brachial plexus.
- Function: fixes the clavicle during movement of the shoulder joint.
Clavipectoral Fascia
- A thickened membrane of deep fascia located between the subclavius and pectoralis minor.
- Pierced by the lateral pectoral nerve, thoracoacromial artery, cephalic vein, and a few lymph vessels.
Serratus Anterior
- Originates from the upper eight ribs.
- Inserts into the anterior aspect of the medial border and inferior angle of the scapula.
- Innervated by the long thoracic nerve (from roots of the brachial plexus, C5, 6, 7).
- Function: draws the scapula forward in boxing (protrusion), rotates the scapula outwards in raising the arm above 90 degrees.
Axilla
- A pyramid-shaped space between the upper part of the arm and the side of the chest.
- Serves as a passage for major neurovascular structures between the neck and thorax and the upper limbs.
- Consists of an apex, a base, and four walls.
Boundaries of the Axilla
-
Apex: directed upwards and medially to the root of the neck, also known as the cervicoaxillary canal.
- Bounded by the clavicle, upper border of the scapula, and outer border of the first rib.
-
Base: formed by skin stretching between the anterior and posterior walls.
- Bounded anteriorly by the anterior axillary fold (formed by the lower border of the pectoralis major).
- Bounded posteriorly by the posterior axillary fold (formed by the tendons of the latissimus dorsi and teres major).
- Bounded medially by upper 4 to 5 ribs and the chest wall.
Walls of the Axilla
- Anterior Wall: formed by the pectoralis major, pectoralis minor, subclavius, and clavipectoral fascia.
- Posterior Wall: formed by the subscapularis, latissimus dorsi, and teres major muscles.
- Medial Wall: wide and formed by the serratus anterior, upper 4-5 ribs, and intercostal muscles.
- Lateral Wall: narrow and formed by the coracobrachialis, biceps brachii, and bicipital groove of the humerus.
Contents of the Axilla
- Brachial Plexus: cords and branches of the brachial plexus.
- Axillary Artery: the axillary artery and its branches.
- Axillary Vein: the axillary vein and its tributaries.
- Axillary Lymph Nodes.
- Axillary Fat.
- Loose Connective Tissue.
- The neurovascular bundle is enclosed in a connective tissue sheath, called the 'axillary sheath'.
Brachial Plexus
- A network of nerves that originates at the root of the neck and enters the upper limb.
- Located in the posterior triangle of the neck and the axilla.
- Formed by the union of the anterior rami of the 5th, 6th, 7th, 8th cervical, and 1st thoracic spinal nerves.
Formation of the Brachial Plexus
- Roots of C5 and C6 unite to form the Upper trunk.
- Root of C7 continues as the Middle trunk.
- Roots of C8 and T1 unite to form the Lower trunk.
Stages of the Brachial Plexus
- Roots: in the posterior triangle.
- Trunks: in the posterior triangle.
- Divisions: behind the clavicle (in the cervicoaxillary canal).
- Cords: in the axilla.
- Branches: in the axilla.
- The first two stages (roots and trunks) lie in the posterior triangle while the last two stages (cords and branches) lie in the axilla.
Brachial Plexus Cords
- The anterior divisions of the upper and middle trunks unite to form the Lateral cord.
- The anterior division of the lower trunk continues as the Medial cord.
- All the posterior divisions of the three trunks join to form the Posterior cord.
Branches of the Brachial Plexus
- Lateral Cord: Lateral Pectoral Nerve, Musculocutaneous Nerve, Median nerve (lateral root).
- Medial Cord: Medial Pectoral Nerve, Ulnar Nerve, Median nerve (medial root), Medial cutaneous nerve of arm and forearm.
- Posterior Cord: Axillary Nerve, Radial Nerve, Upper and Lower Subscapular Nerves, Thoracodorsal or N. to latissimus dorsi.
Summary
- Muscles of the pectoral region connect the upper limb with the anterior and lateral thoracic wall: Pectoralis major, Pectoralis minor, Subclavius, Serratus anterior.
- The axilla is a pyramidal space located between the upper part of the arm and the side of the chest. It has 4 walls (anterior, posterior, medial, and lateral), a base, and an apex.
- The axilla is an important space because it transmits the neurovascular bundle from the neck and thorax to the upper limb.
- It contains: Axillary vessels, cords and branches of the brachial plexus, axillary lymph nodes.
Winging of the Scapula
- Lesion of Long Thoracic Nerve: Paralysis of Serratus anterior muscle can cause winging of the scapula.
- Dislocation of Shoulder Joint: Weakness of muscles on the anterior thoracic wall can lead to winging of the scapula.
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