Sternocleidomastoid

• O (origin):

  • Sternal head: upper surface manubrium
  • Clavicular head: upper surface medial 1/3 clavicle

  A) sternocleidomastoid

  
• R (direction):

  • Upwards

  A) sternocleidomastoid

  
• I (insertions):

  • Mastoid process of skull

  A) sternocleidomastoid

  
• A (actions):

  • Assists with respiration
  • Bilateral action: neck flexion (posterior fibres may also extend head on neck at atlantooccipital joint)
  • Unilateral action: ipsilateral lateral flexion and contralateral rotation

  A) sternocleidomastoid

  
• NS (nerve supply):

  • Motor: Spinal part of accessory nerve (cranial nerve 11)
  • Sensory: Ventral rami C2, C3

  A) sternocleidomastoid