Muscles of the Thoracic Wall

Overview

• Focus on muscles attaching to the thoracic cage and intercostal spaces.

Muscles Outside the Ribcage

1. Serratus Anterior

• Location: Lateral and anterior side of the thoracic wall.
• Origin: Upper ribs (1st 8-9 ribs).
• Insertion: Medial border of the scapula (costal surface).
• Innervation: Long thoracic nerve.
• Function: Protracts and stabilizes scapula; pulls scapula forward.

2. Serratus Posterior Superior

• Location: Back of the thoracic wall.
• Origin: Spinous processes of C7 to T3.
• Insertion: Upper borders of the 2nd to 5th ribs.
• Innervation: Corresponding intercostal nerves (T2 to T5).
• Function: Elevates ribs; assists in inspiration.

3. Serratus Posterior Inferior

• Origin: Spinous processes of T11 to L2.
• Insertion: Lower ribs (9th to 12th ribs).
• Innervation: Corresponding intercostal nerves (T9 to T12).
• Function: Depresses lower ribs; aids in forced expiration.

Intercostal Muscles

1. External Intercostal

• Location: Between ribs, superficial layer.
• Fiber Orientation: Inferiorly and medially (hands in pockets).
• Special Feature: Ends anteriorly as an aponeurosis (external intercostal membrane).
• Function: Important for inspiration.

2. Internal Intercostal

• Location: Deep to external intercostals.
• Fiber Orientation: Superiorly and medially (hands on tits).
• Function: Important for expiration.

3. Innermost Intercostal

• Location: Deep to internal intercostals.
• Fiber Orientation: Same as internal intercostals (superiorly and medially).
• Function: Assists in expiration.

Neurovascular Bundle

• Location: Between internal and innermost intercostal muscles.
• Structures: Intercostal vein, artery, and nerve in the subcostal groove.
• Mnemonic: V.A.N. (Vein, Artery, Nerve from superior to inferior).

Additional Muscles

1. Levatores Costarum

• Location: 12 small muscles connecting transverse processes to the rib below.
• Function: Assist in elevation of the thoracic rib cage.

2. Subcostalis

• Location: Attaches from one rib to the rib below, located internally.

3. Transversus Thoracis

• Origin: Body of the sternum, xiphoid process, and costal cartilages.
• Insertion: Internally on ribs 2 to 6.
• Function: Pulls ribs down.

Summary

• The thoracic wall consists of several crucial muscles that assist in respiration and stabilize the thoracic structure.