The accumulation of alpha and gamma motor neurons forming the accesorius nucleus. The nucleus is located in the lower part of the medulla and then extends down into the first five segments of the cervical spinal cord. The core is located at the site of the lateral horn of the gray spinal cord. The axons penetrate the white matter of the lateral cord and make their way out of the spinal cord at the level of the dental ligaments, forming the spinal part of the nervus accessorius.
The nucleus controls the activity of the nodule muscle (m. sterno-cleido-mastoideus) and the coat muscle (m. trapezius).
Notice that an activation of m. sterno-cleido-mastoideus causes the head to turn to the opposite side: the right m. sterno-cleido-mastoideus thus turns the head to the left and vice versa.