Must Know
- All intrinsic back muscles are supplied segmentally by posterior rami of spinal nerves.
- Layers from deep to superficial are interspinales and intertransversarii, transversospinalis, then erector spinae.
- Transversospinalis is rotatores, multifidus and semispinalis, running from transverse processes to spines.
- Erector spinae is iliocostalis laterally, longissimus in the middle and spinalis medially.
- Erector spinae arises from the back of the sacrum and inner iliac crest, deep to the thoracolumbar fascia.
- Semispinalis capitis is the chief extensor of the head.
- Splenius binds down the deep neck extensors, deep to trapezius and sternocleidomastoid.
- The suboccipital triangle lies above the large spine of C2.
Extensor Muscles
| Muscle | Attachments | Exam point |
|---|---|---|
| Rotatores | Transverse process to root of spine above | Found only in the thoracic spine |
| Multifidus | Sacrum, lumbar mamillary processes, thoracic transverse and cervical articular processes to spines 2 or 3 levels up | Sacrum to upper neck |
| Semispinalis capitis | Upper six thoracic transverse and lower four cervical articular processes to occiput between nuchal lines | Chief head extensor. Pierced by greater occipital nerve |
| Semispinalis cervicis | Upper thoracic transverse processes to cervical spines | Highest fibres insert into the bifid C2 spine |
| Iliocostalis | Sacrum and iliac crest to rib angles and lower cervical transverse processes | Most lateral column |
| Longissimus capitis | Lower cervical transverse processes to mastoid | Deep to splenius capitis |
| Splenius capitis | Ligamentum nuchae and upper thoracic spines to mastoid and lateral superior nuchal line | Rotates and laterally flexes head |
- The ligamentum nuchae runs from external occipital crest to the C7 spine and separates the two sides.
- Thoracolumbar fascia posterior layer attaches to median and lateral sacral crests over erector spinae.
Suboccipital Triangle
| Part | Structures |
|---|---|
| Superomedial boundary | Rectus capitis posterior major |
| Superolateral boundary | Obliquus capitis superior |
| Inferior boundary | Obliquus capitis inferior |
| Floor | Posterior arch of atlas and posterior atlanto-occipital membrane |
| Crossing the floor | Third part of vertebral artery. C1 posterior ramus emerging |
| Crossing the roof | Greater occipital nerve (C2) and occipital artery |
- Both recti and both obliques are supplied by the C1 posterior ramus.
- The C1 rami have no cutaneous branch.
- Inferior oblique runs from the C2 spine to the atlas transverse process and turns the head to its own side.
- Superior oblique runs from the atlas transverse process to the occiput and laterally flexes the head.
- Rectus capitis posterior minor is the only muscle attached to the posterior arch of the atlas.
- The greater occipital nerve hooks under inferior oblique, pierces semispinalis capitis and supplies scalp to the vertex.
Vertebral Artery in the Neck
- The second part climbs through the transverse foramina of C6 to C1, in front of the emerging nerves.
- It gives a spinal branch into each intervertebral foramen.
- Its course is vertical from C6 to C2, then swings laterally between axis and atlas.
- The C2 transverse foramen points upwards and outwards, giving the artery its lateral bend.
- The lateral loop takes up slack during atlantoaxial rotation.
- The third part curves behind the atlas lateral mass and grooves the upper surface of the posterior arch.
- It pierces the lateral posterior atlanto-occipital membrane and enters the foramen magnum.
- The lateral membrane edge can ossify, roofing the groove into a foramen.
- The C1 posterior ramus lies between artery and bone in that groove.
- A venous plexus around the second and third parts forms the vertebral veins.
- Vertebral veins leave through C6 with the artery and alone through C7 to the brachiocephalic vein.
More on the back of the neck
- Beneath trapezius and sternocleidomastoid lies splenius, then longissimus capitis and semispinalis capitis.
- The occipital artery runs deep to digastric and longissimus capitis along the occipitomastoid suture.
- Semispinalis capitis carries a rich venous plexus around and within it.
Numbers to Remember
- Rotatores span one level. Multifidus spans 2 or 3. Semispinalis thoracis spans 6 or more.
- Vertebral artery enters at C6 in most people.
- Iliocostalis inserts on the lower six rib angles.
Memory Aids
- I Love Spines. Iliocostalis, longissimus, spinalis from lateral to medial.
- Major, Superior, Inferior. The three borders of the suboccipital triangle.
Exam Traps
- The vertebral artery does not pass through the C7 transverse foramen.
- The greater occipital nerve is a C2 posterior ramus, not C1.
- Rotatores exist only in the thoracic spine.
- Suboccipital muscles take C1, not the greater occipital nerve.
Source
Sinnatamby CS. Head and neck and spine. In. Last’s Anatomy. Regional and Applied. 12th ed. Edinburgh, Churchill Livingstone Elsevier, 2011.
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 17 October 2026.