Pectoral Muscles Anatomy Quiz

Pectoral Muscles

• Pectoralis Major:

  • Origin (Sternocostal head): Anterior surface of sternum, front of upper 6 costal cartilages, aponeurosis of external abdominal oblique muscle.
  • Origin (Clavicular head): Anterior surface of medial half of clavicle.
  • Insertion: Lateral lip of bicipital groove.
  • Action: Adduction, medial rotation, flexion (clavicular head), extension of flexed arm (sternocostal head).
  • Nerve Supply: Lateral and medial pectoral nerves.

• Pectoralis Minor:

  • Origin: Outer surfaces of 3rd, 4th, and 5th ribs.
  • Insertion: Anterior surface of medial border of coracoid process.
  • Action: Protraction of shoulder girdle, depression of shoulder, forced inspiration (scapula fixed).
  • Nerve Supply: Medial pectoral nerve.

• Subclavius:

  • Origin: Upper surface of 1st costochondral junction.
  • Insertion: A groove on the inferior surface of middle third of clavicle.
  • Action: Steadies the clavicle.
  • Nerve Supply: Nerve to subclavius (C5).

• Serratus Anterior:

  • Origin: Missing from the document.
  • Insertion: Missing from the document.
  • Action: Missing from the document.
  • Nerve Supply: Missing from the document.

Muscles of the Back

• Trapezius:

  • Origin: Back of the skull (external occipital protuberance, medial third of superior nuchal line), back of neck (ligamentum nuchae and spinous processes of 7th cervical and upper thoracic vertebrae), back of thorax (spines of all thoracic vertebrae and supraspinous ligaments).
  • Insertion: V-shaped insertion (upper fibers: posterior border of lateral third of clavicle; middle fibers: medial border of acromion process, upper lip of crest of spine of scapula; lower fibers: rough tubercle on the crest of spine of scapula).
  • Action: As a whole: maintain shoulder level, upper fibers: elevation, upper and lower fibers: upward rotation of scapula; middle fibers: retraction of scapula (bring the shoulder backward).
  • Nerve Supply: Motor: spinal root of accessory nerve; sensory: C3, C4.

• Latissimus Dorsi:

  • Origin: Lower 6 thoracic vertebrae, thoracolumbar fascia, posterior part of outer lip of iliac crest, outer surface of lower 4 ribs, dorsal aspect of inferior angle of scapula.
  • Insertion: Floor of bicipital groove.
  • Action: Adduction, extension, medial rotation; accessory muscle of forced expiration.
  • Nerve Supply: Nerve to latissimus dorsi (thoracodorsal nerve).

• Levator Scapulae:

  • Origin: Transverse processes of upper 4 cervical vertebrae.
  • Insertion: Dorsal surface of medial border of scapula, above root of spine
  • Action: Elevation, retraction, downward rotation of scapula.
  • Nerve Supply: Motor: Nerve to rhomboids (C5); Dorsal Scapular nerve, sensory C3, C4

• Rhomboideus Minor:

  • Origin: Nuchal ligament, C7, T1 spines.
  • Insertion: Dorsal surface of medial border scapula.
  • Action: Retraction, downward rotation of scapula.
  • Nerve Supply: Nerve to rhomboids.

• Rhomboideus Major:

  • Origin: T2, T3, T4, T5 and their supraspinous ligaments.
  • Insertion: Dorsal surface of medial border of scapula, below root of spine
  • Action: Retraction, downward rotation of scapula.
  • Nerve Supply: Nerve to rhomboids.

Clinical Importance

• Trapezius: Paralysis leads to shoulder drop.

Sports and Muscles

• Latissimus Dorsi: Swimming, rowing, climbing.