Splenius capitis: the strap muscle that extends and turns the head

What it is

A flat bandage-like muscle on the back of the neck.

Location

Originates from the lower half of the ligamentum nuchae and spinous processes of C7 to T3 and inserts onto the mastoid process and lateral superior nuchal line.

Function

Extends the head and neck; acting on one side it rotates and bends the head to the same side.

Body system

Muscular · paired (left and right)

FMA ID

FMA22728 (Foundational Model of Anatomy)

Key facts

• Innervation: dorsal rami of the middle cervical spinal nerves
• It is covered by trapezius and sternocleidomastoid and covers the deep neck muscles like a bandage (splenion is Greek for bandage).
• Its mastoid insertion lies deep to the sternocleidomastoid insertion.

Splenius capitis arises from the lower half of the nuchal ligament (ligamentum nuchae, the fibrous midline ligament of the back of the neck) and from the spinous processes of C7 to T3. Its fibres run upwards and laterally. It inserts into the mastoid process of the temporal bone and onto the outer surface of the occipital bone just below the superior nuchal line. (Kenhub: Splenius capitis muscle.)

Radiopaedia gives a slightly fuller description of the origin: the ligamentum nuchae, the tips of the spinous processes and supraspinous ligaments of C7 and of the upper three to four thoracic vertebrae. It places the occipital insertion on the rough surface below the lateral third of the superior nuchal line. (Radiopaedia: Splenius capitis muscle.)

Sources differ on the lowest vertebra involved. TeachMeAnatomy gives C7 to T3 or T4, and a 2024 study in Biomolecules and Biomedicine describes the origin as the spinous processes of the lower four cervical and upper three thoracic vertebrae. (TeachMeAnatomy: The Intrinsic Back Muscles.)

Splenius capitis lies deep to trapezius, and its upper part is covered by sternocleidomastoid. It lies over (superficial to) semispinalis capitis and longissimus capitis. Between the borders of trapezius and sternocleidomastoid it is not covered by either, and there it forms part of the floor of the posterior triangle of the neck. (Kenhub: Splenius capitis muscle.)

The other muscles in the floor of the posterior triangle are levator scapulae and the anterior, middle and posterior scalenes. The triangle is bounded by sternocleidomastoid in front, trapezius behind and the middle third of the clavicle below, and the accessory nerve (cranial nerve XI) runs across it fairly superficially. (TeachMeAnatomy: The Posterior Triangle of the Neck.)

Deeper still, beneath semispinalis capitis, lies the suboccipital triangle. Semispinalis capitis forms its roof, and its borders are rectus capitis posterior major, obliquus capitis superior and obliquus capitis inferior. It contains the vertebral artery and the suboccipital nerve. Splenius capitis is therefore two muscle layers above this triangle. (TeachMeAnatomy: The Suboccipital Muscles.)

Splenius capitis is an intrinsic (true) back muscle, so it is supplied by posterior (dorsal) rami of spinal nerves. Kenhub names the lateral branches of the posterior rami of C2 and C3. (Kenhub: Splenius capitis muscle.)

Radiopaedia also gives the lateral branches of the second and third cervical dorsal rami. TeachMeAnatomy gives the posterior rami of C3 and C4 instead. The safest summary is that the muscle is supplied by posterior rami of the middle cervical spinal nerves, with C3 common to both descriptions. (Radiopaedia: Splenius capitis muscle.)

Its blood comes mainly from muscular branches of the occipital artery, a branch of the external carotid artery. Radiopaedia also lists the descending branch of the occipital artery and the deep cervical artery. (Kenhub: Splenius capitis muscle.)

The descending branch of the occipital artery arises behind the posterior belly of the digastric muscle and sends muscular branches to the deep muscles at the back of the neck, including semispinalis capitis, splenius capitis and splenius cervicis. (Kenhub: Occipital artery.)

When both splenius capitis muscles contract together, they extend the head on the neck, tipping the face upwards. When one contracts on its own, working with the sternocleidomastoid of the opposite side, it bends the head to its own side (lateral flexion) and rotates it to its own side. (Kenhub: Splenius capitis muscle.)

This is the reverse of sternocleidomastoid. One sternocleidomastoid bends the neck to its own side but turns the head to the opposite side. So when you turn your head to the left, the left splenius capitis and the right sternocleidomastoid work together. (Kenhub: Sternocleidomastoid muscle.)

Splenius capitis also helps hold the head and neck still, for example when lying face down and lifting the head. Its fibre make-up fits this postural role: in muscle from 13 young adult men examined after death, 51.2% of splenius capitis fibres were type 1 (slow, fatigue-resistant) fibres, compared with 39.7% in the vastus lateralis of the thigh, and its fibres were narrower. (Pollak N et al. Fiber-type composition and 3D capillary analysis of the human splenius capitis muscle. Biomol Biomed. 2024.)

The two splenius muscles are deep (intrinsic) back muscles. Both start at the midline and run upwards and outwards. The difference is where they end: splenius capitis ends on the head (capitis means 'of the head') and splenius cervicis ends on the cervical vertebrae (cervicis means 'of the neck'). (OpenStax Anatomy and Physiology 2e, 11.3: Axial Muscles of the Head, Neck, and Back.)

Splenius cervicis arises lower down, from the spinous processes of T3 to T6, and inserts on the tubercles of the transverse processes of C1 to C3. It is supplied by the lateral branches of the posterior rami of the lower cervical spinal nerves. Acting on one side it bends and rotates the neck to the same side; acting together the two muscles help trapezius extend the neck. Like splenius capitis, it lies superficial to semispinalis capitis and longissimus capitis and deep to sternocleidomastoid and trapezius. (Kenhub: Splenius cervicis muscle.)

Altered splenius capitis function has been linked to forward head and rounded shoulder posture. Studies of people with neck pain have reported changed activity, atrophy and fat infiltration in the muscle, and it has also been associated with chronic tension-type headache. (Pollak N et al. Fiber-type composition and 3D capillary analysis of the human splenius capitis muscle. Biomol Biomed. 2024.)

In cervical dystonia, a movement disorder in which neck muscles contract involuntarily, botulinum toxin is injected into the overactive muscles. For torticollis, in which the head is turned to one side, the muscles traditionally injected are the splenius capitis on the side the chin turns towards and the sternocleidomastoid on the opposite side, matching the way these two muscles turn the head together. (Jost WH. Torticaput versus Torticollis: Clinical Effects with Modified Classification and Muscle Selection. Tremor Other Hyperkinet Mov. 2019.)

Jost proposed separating torticollis (rotation of the neck on the trunk) from torticaput (rotation of the head on the neck). In patients reclassified as torticaput, the splenius capitis injection was replaced by injections into the opposite sternocleidomastoid and trapezius and the same-side obliquus capitis inferior, which improved results in that group. (Jost WH. Torticaput versus Torticollis: Clinical Effects with Modified Classification and Muscle Selection. Tremor Other Hyperkinet Mov. 2019.)

The nearest named structures in the 3D model, measured from the centre of each part:

• Levator scapulae · muscular
• Spinalis · muscular
• Cervical rotator · muscular
• Longissimus capitis · muscular
• Seventh cervical vertebra · skeletal
• Sixth cervical vertebra · skeletal
• Deep cervical artery · cardiovascular
• Semispinalis cervicis · muscular
• Interspinales cervicis · muscular
• Fifth cervical vertebra · skeletal