Human Anatomy
Back Region
Back region anatomy for MBBS: extrinsic and intrinsic back muscles, suboccipital triangle, vertebral venous plexus and lumbar puncture, mapped to NMC codes AN42.1 to AN42.3.
MedNext Academy | 3 min read
Back Region
Back region anatomy for MBBS: extrinsic and intrinsic back muscles, suboccipital triangle, vertebral venous plexus and lumbar puncture, mapped to NMC codes AN42.1 to AN42.3.
The back region chapter separates the superficial extrinsic muscles that move the limb from the deep intrinsic muscles that support the spine, and covers the suboccipital triangle and the vertebral venous plexus. It underpins the anatomy of lumbar puncture, back pain and metastatic spread to the spine.
High-yield: Back Region
- The muscles of the back are divided into superficial extrinsic muscles and deep intrinsic muscles.
- The extrinsic muscles, such as trapezius and latissimus dorsi, move the upper limb and are supplied by ventral rami.
- The intrinsic muscles maintain posture and move the vertebral column and are supplied by dorsal rami.
- The erector spinae is the large intrinsic muscle running vertically on each side of the spine.
- The suboccipital triangle lies deep in the upper neck and contains the vertebral artery and the suboccipital nerve.
- The boundaries of the suboccipital triangle are rectus capitis posterior major, obliquus capitis superior and obliquus capitis inferior.
- The vertebral artery runs across the floor of the suboccipital triangle before entering the skull.
- The dorsal rami of spinal nerves supply the skin and the intrinsic muscles of the back.
- The vertebral venous plexus around the spine has no valves and can carry tumour or infection to the vertebrae.
- Prostate cancer can spread to the vertebral column through this valveless vertebral venous plexus.
- The ligamentum flavum connects adjacent laminae and is pierced during a lumbar puncture.
- A lumbar puncture is done below the second lumbar vertebra to avoid the spinal cord, which ends at that level in adults.
- The triangle of auscultation, near the medial border of the scapula, is a thin area where breath sounds are heard clearly.
- The thoracolumbar fascia gives origin to several back and abdominal muscles and encloses the deep back muscles.
Extrinsic versus intrinsic back muscles
- **Extrinsic muscles:** Trapezius, latissimus dorsi and rhomboids. Move the upper limb. Supplied by ventral rami.
- **Intrinsic muscles:** Erector spinae and deeper groups. Move and support the spine. Supplied by dorsal rami.
- **Suboccipital triangle:** Contains the vertebral artery and the suboccipital nerve deep in the upper neck.
- **Vertebral venous plexus:** Valveless veins that can carry cancer and infection to the vertebrae.
NMC competencies in this chapter
- **AN42.1:** Superficial and deep muscles of the back and their nerve supply
- **AN42.2:** Suboccipital triangle: boundaries and contents
- **AN42.3:** Applied anatomy of the back including the vertebral venous plexus
Frequently Asked Questions
Why is the suboccipital triangle important?
It contains the third part of the vertebral artery and the suboccipital nerve, and it is a key landmark for the artery as it prepares to enter the skull.
How does prostate cancer reach the spine?
The vertebral venous plexus has no valves and connects with the pelvic veins, so tumour cells and infection can travel through it to the vertebral column.
Why is a lumbar puncture done in the lower back?
The spinal cord ends around the first or second lumbar vertebra in adults, so a needle placed below this level enters the cerebrospinal fluid without harming the cord.
How does this chapter help in NEET-PG?
The vertebral venous plexus, lumbar puncture landmarks and back muscle innervation appear in surgery, oncology and anaesthesia, so this region carries into PG questions.
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