Overview
This lecture covers the anatomy, attachments, innervation, and actions of the erector spinae muscle group, highlighting its three main muscles and their subdivisions.
Erector Spinae Muscle Group Overview
- The erector spinae consists of three main muscles: spinalis (medial), longissimus (middle), and iliocostalis (lateral).
- Each muscle is divided into three sections, often named capitis, cervicis, thoracis, or lumborum (for iliocostalis).
Origins and Insertions
- Spinalis:
- Capitis originates from C6-T2 spinous processes and nuchal ligament, inserts on occiput.
- Cervicis originates from C7-T1 spinous processes and nuchal ligament, inserts on C2-C3.
- Thoracis originates from T11-L2 spinous processes, inserts on T2-T8 spinous processes.
- Longissimus:
- Capitis originates from C4-T4 transverse processes, inserts on mastoid process.
- Cervicis originates from T1-T4 transverse processes, inserts on C2-C6 transverse processes.
- Thoracis originates from posterior superior iliac spine, sacrum, L1-L5 transverse processes, inserts on T1-T12 transverse processes and ribs 3-12.
- Iliocostalis:
- Cervicis originates from ribs 3-6, inserts on C4-C6 transverse processes.
- Thoracis originates from ribs 7-12, inserts on ribs 1-6 and C7 transverse process.
- Lumborum originates from iliac crest and lateral sacral crest, inserts on L1-L4 transverse processes, ribs 4-12, and thoracolumbar fascia.
Innervation
- All erector spinae muscles are innervated by the dorsal (posterior) rami of their corresponding spinal nerves.
- Each segment of muscle is innervated by the spinal nerve at its vertebral level.
Actions
- Bilateral contraction of erector spinae extends the trunk and neck.
- Unilateral contraction causes lateral flexion of the trunk and neck.
- Muscle actions are limited to regions where that particular muscle is present.
Key Terms & Definitions
- Erector Spinae — Group of three muscles running along the vertebral column responsible for extending and laterally flexing the spine.
- Spinous Process — Bony projection off the posterior (back) of each vertebra.
- Transverse Process — Lateral projections from the vertebrae.
- Nuchal Ligament — Ligament along the back of the neck serving as muscle attachment.
- Dorsal (Posterior) Ramus — Back branch of a spinal nerve supplying muscles and skin of the back.
- Thoracolumbar Fascia — Large connective tissue structure in the lower back.
Action Items / Next Steps
- Review diagrams or videos focusing on each erector spinae muscle individually for more detail.
- Memorize the origins, insertions, and actions of each section for exam preparation.