Nucleus of accessory nerve

Nucleus of accessory nerve (a.k.a. spinal accessory nucleus or accessory nucleus proper) is an example of the central group of nuclei found within the anterior horns of cervical segments of the spinal cord. The rootlets of nucleus of accessory nerve ascend as the spinal accessory nerve, which passes through the foramen magnum to enter the cranial cavity. Here, it coalesces with the cranial accessory nerve that originates from the nucleus ambiguous in the medulla oblongata. The combined accessory nerve exits the cranial cavity via the foramen magnum, following which the efferent neurons of the nucleus of accessory nerve (spinal accessory nucleus) innervate two important muscles, namely the trapezius and the sternocleidomastoid.

The nucleus of accessory nerve–along with the nucleus of phrenic nerve–is sandwiched between the medial and lateral group of cells in the cervical anterior horn, which innervate the neck and upper limb musculature, respectively.