The back muscles are categorized into three major groups based on their location and function:
Classification of Back Muscles
- Superficial Group
- Associated with: Shoulder movements.
- Development: Extrinsic, as they do not develop embryologically in the back.
- Intermediate Group
- Associated with: Movements of the thoracic cage.
- Development: Extrinsic, similar to the superficial group.
- Deep Group
- Associated with: Movements of the vertebral column.
- Development: Intrinsic, as they develop embryologically in the back.
This guide focuses on the intermediate back muscles, including their attachments, innervation, and functions.
Intermediate Back Muscles
The intermediate group comprises two muscles:
- Serratus Posterior Superior
- Serratus Posterior Inferior
These muscles extend from the vertebral column to the rib cage and contribute slightly to respiratory functions by elevating or depressing the ribs.
Serratus Posterior Superior
- Shape: Thin and rectangular.
- Location: Lies deep into the rhomboid muscles in the upper back.
| Feature | Details |
|---|---|
| Attachments | Originates from the lower ligamentum nuchae and cervical/thoracic spines (C7–T3); attaches to ribs 2–5 in an inferolateral direction. |
| Actions | Elevates ribs 2–5. |
| Innervation | Intercostal nerves. |
Serratus Posterior Inferior
- Shape: Broad and strong.
- Location: Lies underneath the latissimus dorsi.
| Feature | Details |
|---|---|
| Attachments | Originates from thoracic and lumbar spines (T11–L3); attaches to ribs 9–12 in a superolateral direction. |
| Actions | Depresses ribs 9–12. |
| Innervation | Intercostal nerves. |
Key Points to Remember
- Intermediate muscles are extrinsic, meaning they develop outside the back and migrate during embryogenesis.
- Function: These muscles primarily assist with thoracic cage movement and may play a minor role in respiration.
- Innervation: Both muscles are innervated by the intercostal nerves.
- Serratus Posterior Superior: Elevates ribs 2–5 for inspiration.
- Serratus Posterior Inferior: Depresses ribs 9–12 for expiration.
