Your cart is currently empty!
M01.05.008 Thoracic Cage
The thoracic wall forms the anterior, posterior, and lateral boundaries of the thorax. It consists of five primary muscles that change the volume of the thoracic cavity during respiration. Additionally, accessory muscles of respiration, while not part of the thoracic wall, attach to it and play a supportive role.
Muscles of the Thoracic Wall
Primary Muscles
- External Intercostals
- Internal Intercostals
- Innermost Intercostals
- Subcostals
- Transversus Thoracis
Accessory Muscles of Respiration
- Pectoralis major
- Pectoralis minor
- Serratus anterior
- Scalene muscles
Detailed Anatomy
External Intercostals
- Attachments: Originates at the lower border of each rib, inserting onto the superior border of the rib below.
- Actions: Stabilizes rib position during normal respiration and elevates ribs, increasing thoracic volume during forced inspiration.
- Innervation: Intercostal nerves (T1-T11).
| Feature | Description |
|---|---|
| Fiber Direction | Inferoanteriorly |
| Function | Elevates ribs during inspiration |
| Clinical Relevance | Paralysis may impair deep breathing. |
Internal Intercostals
- Attachments: Originates from the lateral edge of the costal groove, inserted onto the superior surface of the rib below.
- Actions: Stabilizes rib position during respiration and depresses ribs, decreasing thoracic volume during forced expiration.
- Innervation: Intercostal nerves (T1-T11).
| Feature | Description |
|---|---|
| Fiber Direction | Inferoposteriorly |
| Function | Depresses ribs during expiration |
| Clinical Relevance | Overactivity may contribute to dyspnea in conditions like COPD. |
Innermost Intercostals
- Attachments: Originates from the medial edge of the costal groove and inserts onto the superior surface of the rib below.
- Actions: Similar to the internal intercostals, depresses ribs during forced expiration.
- Innervation: Intercostal nerves (T1-T11).
| Feature | Description |
|---|---|
| Location | Deepest layer of intercostal muscles |
| Separation | By intercostal neurovascular bundle |
Subcostals
- Attachments: Originates from the inferior surface of lower ribs, attaching to the superior border of the second or third rib below.
- Actions: Stabilizes rib position and depresses ribs during forced expiration.
- Innervation: Intercostal nerves.
| Feature | Description |
|---|---|
| Location | Inferior thoracic wall |
| Fiber Orientation | Similar to innermost intercostals |
Transversus Thoracic
- Attachments: Arises from the posterior surface of the inferior sternum and lower costal cartilages, ascending to attach to internal surfaces of costal cartilages 2-6.
- Actions: Weakly depresses ribs during expiration.
- Innervation: Intercostal nerves (T2-T6).
| Feature | Description |
|---|---|
| Location | Internal surface of thoracic wall |
| Continuity | With transversus abdominis inferiorly |
Points to Remember
- Intercostal Muscles: Three layers (external, internal, innermost) stabilize ribs and modulate thoracic volume during respiration.
- Accessory Muscles: Provide additional respiratory support, especially during increased respiratory demand.
- Clinical Importance: Dysfunction in thoracic wall muscles can compromise breathing mechanics, as seen in respiratory diseases.
Bibliography
- TeachMeSeries Ltd. “Thoracic Wall Muscles Anatomy.” 2024.
- Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 41st Edition.