Superficial Muscles of the Thorax Quiz

Superficial Muscles of the Thorax

• Subclavius: Located beneath the clavicle, originates from the 1st rib and inserts on the lower surface of the clavicle. It stabilizes the clavicle by pulling it downwards.
• Serratus Anterior: Large muscle fibers located on the lateral aspect of ribs 1-9. Originates from the external surface of ribs 1-9 and inserts at the medial border of the scapula. Contraction pulls the medial margin of the scapula forward, helping to flex the arm.
• Pectoralis Minor: Located anterior to the serratus anterior, originates from the external surface of ribs 3-5. Inserts at the coracoid process of the scapula. Contraction pulls the shoulder down and medially. Stiffness in this muscle can cause forward shoulder posture.
• Pectoralis Major: Divided into three parts: Clavicular, Sternocostal, and Abdominal. All parts originate from different areas (clavicle, sternum/costal cartilage, abdominal muscles respectively) and insert at the crest of the greater tubercle of the humerus.

Deep Muscles of the Thorax

• Subcostal Muscles: Located on the inside of the thorax. Originate from the lower rib and insert on the upper rib. Contraction pulls the thorax downwards, aiding in expiration.
• Transverse Thoracis Muscle: Originates from the internal surface of the sternum, xiphoid process, and cartilage of ribs 4-7. Inserts at the cartilage of ribs 2-6. Also aids in pulling the chest downwards for expiration.
• Internal Intercostal Muscles: Located between the ribs. Originate from the lower rib and insert into the upper rib. Contraction pulls the chest down for expiration.
• External Intercostal Muscles: Located superficially to the internal intercostal muscles. Originate from the upper rib and insert at the lower rib. Contraction elevates the thorax, aiding in inspiration by expanding the thoracic cavity.
• Levatores Costarum Muscles: Tiny muscles on the back. Divided into two groups:
  • Levatores Costarum Breves: Short levatores costarum, originate from the transverse process of C7 to T11, and insert one rib below.
  • Levatores Costarum Longi: Longer muscles, originate from T8-T11, and insert two ribs below, skipping one rib. Contraction of both groups pulls the thorax up to aid inspiration.