58. Accessory nerve, hypoglossal nerve. Nuclei - position, characteristic. The course of the nerves, branches, area of distribution.

ACCESSORY NERVE (C.N. XI)

• The accessory n. is a unique cranial nerve that has both cranial & spinal roots
• It is primarily a motor nerve.
• Function:

1. Supplies muscles involved in movements of the neck & shoulders

• ↳ Sternocleidomastoid m.
• ↳ Trapezius m.

2. Goes together with the Vagus n. to innervate muscles in the pharanx, larynx & soft palate.

Nuclei:

1. Neucleus Ambigus (cranial root)
2. Spinal accessory nucleus:

• ↳ In the lateral finiculus of upper 6 cervical segments of spinal cord).

Course:

• Fibers from the spinal accessory nucleus going to ascend,① all fibers go together through the Foramen Magnum ②,

1. ③ join the cervical root of the vagus n.
2. ④ Cranial & spinal aspects fuse together and form the trunk of the accessory.
3. ⑤ The trunk exit the cranial cavity through jugular foramen & ⑥ Divides into Internal & External branches.
4. ⑦ The internal br. join the vagus n. at the region of inferior ganglion, to provide with extra motor fibers to pharyngeal br. of the vagus n. to form the pharyngeal plexus. to supply muscles of the pharanx, palate & some br. to recurrent laryngeal n.
5. ⑧ The external br. goes down, on it's way it's going to pick up fibers from the cervical plexus specifically from anterior ramus of C₂, C₃ & C₄ spinal cord segments. then goes to innervate the Sternocleidomastoid & Trapezius m.