Lecture on the 11th Cranial Nerve: The Accessory Nerve

Overview

• Part of a cranial nerve series
• 12 pairs of cranial nerves in total
• Focus on the 11th cranial nerve: Accessory Nerve
• Accessory nerve is purely motor
• Innervates sternocleidomastoid and trapezius muscles
• Works alongside vagus nerve to innervate pharynx, larynx, and soft palate muscles

Nuclei and Roots

• Two main nuclei: Nucleus Ambiguus and Spinal Accessory Nucleus
  • Nucleus Ambiguus: Located in medulla oblongata, gives rise to the cranial root
  • Spinal Accessory Nucleus: Located in the upper 6 segments of the spinal cord's lateral anterior horn of the gray matter, gives rise to the spinal root

Pathway of the Accessory Nerve

• Cranial root exits brainstem through retro-olivary groove
• Spinal root ascends, enters cranium through foramen magnum, fuses with cranial root
• Formed trunk exits cranium through jugular foramen
• Trunk divides into internal and external branches

Internal Branch

• Joins vagus nerve at the inferior ganglion
• Contributes motor fibers to the pharyngeal branch of the vagus nerve
• Helps form the pharyngeal plexus
• Innervates muscles of the soft palate (excluding tensor veli palatini)
• Innervates muscles of the pharynx (excluding stylopharyngeus)
• May join recurrent laryngeal nerve to innervate intrinsic laryngeal muscles

External Branch

• Descends along the neck
• Picks up fibers from anterior rami of C2, C3, and C4 from the cervical plexus
• Innervates the sternocleidomastoid (responsible for head rotation to the contralateral side and flexion to the ipsilateral side)
• Innervates the trapezius (responsible for neck extension, scapula elevation, rotation)

Detailed Anatomy

• Spinal Cord Section:
  • Grey matter: anterior and posterior horns
  • White matter: posterior, anterior, and lateral funiculi
  • Spinal accessory nucleus in lateral anterior horn of grey matter
  • Variations in spinal accessory nucleus location: generally C1-C6
  • Fibers ascend through foramen magnum to join cranial root

Visualization and Summary

• Schematic views provided for better understanding
• Summary of nerve pathway, branches, and innervation

Conclusion

• Next lecture will cover the 12th cranial nerve: Hypoglossal Nerve
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• Thanks and farewell