Xi cranial nerve

Anatomy

1. INTRODUCTION COMPONENTS COURSE OF CRANIAL ROOT COURSE OF SPINAL ROOT DISTRIBUTION OF SPINAL ACCESSORY NERVE CLINICAL FINDINGS LESIONS XI- Cranial Nerve (Accessory )

2. • The Accessory nerve [XI] carries GSE ( General Somatic Efferent) fibers. • Innervates the STERNOCLEIDOMASTIOD and TRAPEZIUS muscles. • Unique cranial nerve - - - roots arise from motor neurons of the UPPER FIVE SEGMENTS [C1-C5] OF THE CERVICAL SPINAL CORD.

3. COMPONENTS: I- Cranial Root. (Nucleus Ambiguous) II- Spinal Root. ( Spinal Nucleus of Ant. Grey columns b/w C1 - C5)

4. CRANIAL ROOT: • Arises from the lower part of N ucleus Ambiguous . • Accessory to the Vagus nerve [X]. • Distributed through the Branches of Vagus nerve .

5. Course of Cranial Root: • Rootlets arising from Caudal part of the Medulla Oblongata on the Anterolateral surface, just inferior to the rootlets arising to form Vagus Nerve. • Leaving the Medulla, Cranial roots course with the “spinal” root of Accessory nerve into the Jugular foramen, and again separates outside the foramen. • Join the Vagus nerve [Inf. Ganglion] after exiting the Jugular foramen, supplying the pharyngeal musculature supplied by Vagus Nerve.

6. Course of the Spinal Root: • Fibers arising from the motor cells in the lateral part of the Anterior column of grey substance of the medulla spinalis as low as fifth cranial nerve[C1-C5]. • Joining together as they ascend. • Enters the Cranial Cavity through Foramen Magnum. • Continues through the Posterior Cranial Fossa, laterally towards Jugular foramen Extra-cranially: • Exits through Jugular foramen. • Descends in the neck, Medial to the Int. Jugular Vein . • B/w the Angle of Mandible and Mastoid process. • Lies under the Stylohyoid and Post. Belly of Digastric muscle.

7. • Crosses the Int. Jugular Vein laterally in 66%, and passes behind in 33.3% of cases. • Disappear either into or beneath the Ant. Border of Sternocleidomastoid muscle. [NO BRANCHES IN ANT. TRIANGLE OF THE NECK] • Continues its descend & Enters the Post. Triangle of the Neck. • Still moving obliquely and downward, within the Investing layer of the Cervical fascia. • Reaches the Ant. Border of Trapezius muscle, terminates by innervating the muscle.

8. Distribution: → Motor Innervation to; • Sternocleidomastoid muscle. • Trapezius muscle.

9. CLINICAL FINDINGS: • Paralysis of Sternocleidomastoid and Trapezius muscle. • Drooping of the Shoulder. • Inability to turn chin to opposite side. • Inability to draw head forward. • Irritation of the nerve during biopsy of enlarged caseous lymph nodes, may produce TORTICOLLIS or WRY NECK. LESIONs: • Penetrating injury to the Posterior Triangle of the Neck. • Superficial location of the nerve in Post. Triangle of the neck makes it susceptible to injury.