Overview
This lecture covers the deep (intrinsic) muscles of the back, their anatomical arrangement, key functions, and related bony landmarks essential for understanding back muscle attachment and movement.
Vertebral Column Anatomy
- The vertebral column consists of 26 bones: cervical (7), thoracic (12), lumbar (5), sacrum (5 fused), and coccyx.
- Key vertebral features: spinous process (central, posterior projection), transverse processes (lateral projections), superior/inferior articular processes, and lamina (connects processes).
- Other important bones: scapulae (shoulder blades), occiput of the skull, pelvis, proximal humerus, and femur.
Deep Layers of Back Muscles
- Deep back muscles are arranged in layers: deepest (transversospinalis group), intermediate (erector spinae), and superficial (spino-transversalis group).
Transversospinalis Group
- Includes rotatores, multifidus, and semispinalis muscles.
- Rotatores: originate from transverse processes and insert into spinous processes above; mainly rotate and stabilize the spine.
- Multifidus: multiple origins from sacrum, lumbar, thoracic, and cervical vertebrae; insert into all spinous processes; stabilizes and extends the vertebral column.
- Semispinalis: runs from transverse processes (c4-t11) to spinous processes (t6-c2) and occiput; extends and rotates head, neck, and trunk.
Erector Spinae Group
- Includes spinalis (medial), longissimus (intermediate), and iliocostalis (lateral).
- All originate from a shared common tendinous origin at lumbar/thoracic vertebrae, sacrum, and pelvic ligaments.
- Spinalis: runs along spinous processes, extends vertebral column.
- Longissimus: runs from transverse to transverse processes and skull, extends/flexes vertebral column.
- Iliocostalis: runs from lower ribs/lumbar vertebrae to cervical vertebrae and ribs, extends and flexes back.
Spino-Transversalis Group
- Splenius capitis: from nuchal ligament and c7-t3 to mastoid process and occipital bone; extends/rotates head.
- Splenius cervicis: from t3-t6 to c1-c3; extends/rotates neck.
Minor Deep Back Muscles
- Interspinales: small muscles between spinous processes, stabilize vertebral column.
- Intertransversarii: between transverse processes, stabilize spine.
- Levatores costarum: from transverse processes (c7-t11) to superior rib borders, lifts ribs for respiration.
Key Terms & Definitions
- Vertebral column — backbone, composed of stacked vertebrae.
- Spinous process — posterior bony projection from a vertebra.
- Transversospinalis — deepest muscle group connecting transverse and spinous processes, rotates/stabilizes spine.
- Erector spinae — primary extensor muscles of the vertebral column.
- Spino-transversalis — group includes splenius muscles; extends/rotates head and neck.
- Interspinales/Intertransversarii — small stabilizing muscles between vertebrae.
Action Items / Next Steps
- Review bony landmarks and muscle attachments discussed.
- Watch the next video for intermediate and superficial back muscles (latissimus dorsi, trapezius).