The muscles of the neck and shoulder can be divided into 5 layers from deep to shallow. The deepest layer is the multifidus and piriformis muscles, which have a more restrictive role than the motor role and can play a role in preventing dislocation of individual vertebrae due to excessive bending or rotation when the spine is flexed. The second layer includes the cervical semispinalis, the longest head muscle, the ramus and the scapularis. The cervical semispinalis and the longest head muscle can play the role of extending the head and lateral flexion of the neck, the ramus is the main muscle that makes the cervical vertebrae lateral flexion, and the scapularis can play the role of elevating the scapula. The third layer is the cephalic semispinalis, which acts similarly to the cervical semispinalis and the longest cephalic muscle. The fourth layer is the cephalic gripper and cervical gripper muscles, which serve to extend the neck and rotate the head to the same side. The most superficial muscle is the trapezius, an important muscle in the back of the neck and back of the shoulder that serves to raise the scapula, rotate the scapula upward, retract the scapula, stretch the head and neck bilaterally, and rotate the head and neck unilaterally.