Muscle Anatomy: Pectoral Region Overview

Pectoral Region Overview

• The pectoral region contains several important muscles contributing to shoulder movement and stabilization.

Pectoralis Major Muscle

• Origin: Two heads
  • Clavicular head: Front of medial half of the clavicle
  • Sternocostal head: Front of the sternum and upper 6 ribs
• Insertion: Lateral lip of bicipital groove via U-shaped bilaminar tendon
• Nerve Supply: Medial and lateral pectoral nerves
• Action:
  • Whole muscle: Adduction and medial rotation of the arm
  • Clavicular head: Flexes arm anteromedially
  • Sternocostal head: Returns fully flexed or extended arm to resting position; assists latissimus dorsi in raising trunk when arm is fixed

Pectoralis Minor Muscle

• Origin: 3rd to 5th ribs near costal cartilages
• Insertion: Medial border and superior surface of coracoid process of scapula
• Action: Stabilizes scapula by drawing it inferiorly and anteriorly against the thoracic wall (protraction of the scapula)
• Innervation: Medial pectoral nerves
• Pectoralis Minor Syndrome: Compression of the brachial plexus over coracoid process, causing pain and numbness

Subclavius Muscle

• Origin: Junction of 1st rib and its costal cartilage (1st costochondral junction)
• Insertion: Groove of subclavius on the inferior surface of the middle third of the clavicle
• Action: Steadies the clavicle during shoulder girdle movements
• Nerve Supply: Nerve to subclavius

Serratus Anterior Muscle

• Origin: Eight digitations from the upper 8 ribs and fascia covering intercostal muscles
• Insertion: Ventral aspect of medial border of the scapula
  • 1st digitation to superior angle of scapula
  • 2nd & 3rd digitations to medial border
  • Lower 5 digitations to inferior angle
• Nerve Supply: Long thoracic nerve (C5,6,7 from brachial plexus)
• Action:
  • Protraction and depression of the scapula
  • Collaborates with trapezius for upward rotation of scapula during arm elevation
  • Can elevate ribs during forced inspiration
• Applied Anatomy: Long thoracic nerve injury leads to serratus anterior paralysis, causing winging of scapula (prominence of medial border not contacting thoracic wall)

Pectoral Fascia

• A thin membrane that invests the pectoralis major muscle
• Attachments:
  • Superiorly to the clavicle

This quiz covers the anatomy and functions of the pectoral region, focusing on the pectoralis major and minor muscles. You will explore their origins, insertions, nerve supply, and actions in relation to shoulder movement and stabilization. Test your knowledge on the crucial roles these muscles play in upper limb dynamics.