Muscles of the Anterior Thorax

Muscles of the Anterior Thorax

• Pectoralis Major: large muscle on the anterior chest, responsible for:

  • Arm flexion at the shoulder joint
  • Arm adduction (pulling arm towards the body) at the shoulder joint
  • Medial rotation of the arm at the shoulder joint
  • Synergists: Coracobrachialis, Latissimus Dorsi, Teres Major, Subscapularis
  • Antagonists: Teres Major, Latissimus Dorsi (for extension), Deltoid, Supraspinatus (for abduction), Infraspinatus, Teres Minor (for lateral rotation)

• External Intercostals: located between ribs, help to:

  • Elevate ribs during inhalation

• Internal Intercostals: located between ribs, help to:

  • Depress ribs during forced exhalation
  • Antagonists: External Intercostals

• Serratus Anterior: located on the side of the chest, responsible for:

  • Protraction of the scapula (moving scapula forward)
  • Synergists: Pectoralis Minor
  • Antagonists: Rhomboids major & minor, Trapezius
  • Also functions in scapular protraction

Deeper Muscles of the Anterior Thorax

• Pectoralis Minor: located underneath Pectoralis Major, responsible for:

  • Protraction of the scapula (moving scapula forward)
  • Synergists: Serratus Anterior

• Subclavius: located beneath the clavicle, responsible for:

  • Depression of the clavicle

Muscles of the Abdominal Wall

• External Oblique: most superficial abdominal muscle, responsible for:

  • Flexion of the vertebral column
  • Compressing abdominal contents to increase intra-abdominal pressure and assist in forced exhalation

• Internal Oblique: located underneath External Oblique, responsible for:

  • Flexion of the vertebral column
  • Compressing abdominal contents to increase intra-abdominal pressure and assist in forced exhalation

• Rectus Abdominis: located between External and Internal obliques, responsible for:

  • Flexion of the vertebral column
  • Compressing abdominal contents to increase intra-abdominal pressure and assist in forced exhalation

• Transversus Abdominis: deepest layer of abdominal wall, responsible for:

  • Compressing abdominal contents to increase intra-abdominal pressure and assist in forced exhalation
  • Does not flex the vertebral column

• Linea Alba: thick band of connective tissue down the center of the abdomen, where some abdominal muscles insert.

• Pyramidalis: small triangular muscle between pubic bone and Linea Alba, functions to tense the Linea Alba.

Muscles of the Posterior Thorax

• Trapezius: large muscle with three portions (descending, transverse, and ascending), responsible for:

  • Elevating the scapula
  • Extending the neck
  • Retracting the scapula

• Infraspinatus: located on the posterior side of the scapula, responsible for:

  • Lateral (external) rotation of the shoulder joint

• Teres Minor: small muscle inferior to the infraspinatus, responsible for:

  • Lateral (external) rotation of the shoulder joint

• Teres Major: Located inferior to the teres minor, responsible for:

  • Extending the arm at the shoulder joint
  • Adducting the shoulder joint
  • Medially rotating the shoulder
  • Origin: Thoracolumbar fascia

• Latissimus Dorsi: large muscle covering the lower back, responsible for:

  • Extending the arm at the shoulder joint
  • Adducting the shoulder joint
  • Medially rotating the shoulder
  • Origin: Thoracolumbar fascia

• Rhomboid Muscles (major & minor): responsible for:

  • Retracting the scapula

• Erector Spinae Muscles (spinalis, longissimus, iliocostalis): responsible for:

  • Extending the vertebral column and neck

• Serratus Posterior Inferior: Located on the lower back, responsible for:

  • Extension of the vertebral column

• Quadratus Lumborum: Located on the lower back, responsible for:

  • Extending the lower back
  • Fixating (stabilizing) the ribs

• Supraspinatus: Located in the supraspinous fossa of the scapula, responsible for:

  • Abduction (movement away from the midline) of the arm at the shoulder joint

• Subscapularis: Located in the subscapular fossa of the scapula, part of the rotator cuff

Rotator Cuff

• Rotator Cuff: comprised of: Supraspinatus, Infraspinatus, Teres minor, Subscapularis
  • Function: Stabilize the shoulder joint

Other

• Thoracolumbar Fascia: Aponeurosis (connective tissue sheet) serving as an origin for the latissimus dorsi muscle

• Splenius Capitis: Extends the neck