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Semispinalis capitis muscle

The semispinalis capitis is a deep, powerful muscle located in the upper back and posterior neck region. It plays a crucial role in movements and stabilization of the head and cervical spine. As part of the transversospinalis group, the semispinalis capitis spans several vertebrae and is instrumental in extending, rotating, and laterally flexing the head. Its anatomical importance also extends to clinical imaging, particularly in the context of neck pain, trauma, or neurological disorders.

Function

  • Extends the head and neck (bilateral contraction)

  • Rotates the head to the opposite side (unilateral contraction)

  • Assists with lateral flexion of the cervical spine

Origin

  • Transverse processes of C7–T6 vertebrae

  • Articular processes of C4–C6 vertebrae

Insertion

  • Between the superior and inferior nuchal lines of the occipital bone (posterior skull)

Nerve Supply

  • Dorsal rami of the cervical spinal nerves (primarily C2—greater occipital nerve, and C3)

Artery Supply

  • Deep cervical artery (branch of the costocervical trunk)

  • Descending branch of the occipital artery

Vein Supply

  • Corresponding veins to the deep cervical and occipital arteries (drain into the vertebral and external jugular veins)

MRI Appearance

  • T1-weighted: Muscle appears isointense to slightly hypointense compared to surrounding soft tissue; clear muscle striations

  • T2-weighted: Normal muscle demonstrates relatively low signal intensity, but increased signal may indicate edema or pathology.

  • STIR (Short Tau Inversion Recovery): Muscle is dark (hypointense) under normal conditions, but pathology (e.g., strain, myositis) causes high signal (bright) areas

CT Appearance

  • Muscle appears as a soft tissue density posterior to the cervical vertebrae

  • Well-defined from adjacent subcutaneous fat; may be less distinguishable in presence of atrophy or significant edema

MRI images

Semispinalis capitis muscle mri axial image