- Divided into three parts: descending (superior), ascending (inferior), and middle
- Origin
- Medial third of the superior nuchal line of the occipital bone
- External occipital protuberance
- Nuchal ligament
- Spinous processes of C7–T12 vertebrae - Insertion
- Lateral third of the clavicle
- Acromion
- Spine of the scapula - Innervation
- Motor: Spinal accessory nerve (CN XI) - Blood Supply
- Transverse cervical artery (branch of thyrocervical trunk)
- Contributions from dorsal scapular and occipital arteries - Actions
- Upper fibres:
- Elevate scapula
- Assist in upward rotation of the scapula
- Middle fibres:
- Retract scapula
- Lower fibres:
- Depress scapula
- Also assist with upward rotation
