Anatomy study note · Head and neck

Accessory nerve

The eleventh cranial nerve (motor). Its spinal root supplies sternocleidomastoid and trapezius; its cranial root joins the vagus.

Key points

• CN XI: spinal root C1–5 → up through the foramen magnum → out the jugular foramen.
• Supplies sternocleidomastoid + trapezius.
• Superficial in the posterior triangle → dropped shoulder.
• Motor nuclei: basal lamina. Sensory nuclei: alar lamina.
• Nerve: epineurium → perineurium (blood–nerve barrier) → endoneurium.
• Cut nerve: Wallerian degeneration; regrows 0.5–3 mm/day.

The full note in the atlas also covers

Course · Histology · Development · Clinical notes

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Written from

• Snell’s Clinical Anatomy by Regions, 10th ed., ch. 12, PDF pp. 1680–1682, 1687; ch. 3, PDF p. 327
• Inderbir Singh’s Human Embryology, ch. 17, PDF pp. 312, 318
• BRS Cell Biology & Histology, 7th ed., ch. 9, PDF pp. 163–166, 166, 171–172

More from the head and neck

• Anterior cerebral artery
• Aqueous humour
• Arteries of the face
• Arytenoid cartilage
• Arytenoid muscles
• Cerebellum
• Cerebrum
• Cervical plexus
• Ciliary body
• Common carotid artery
• Common tendinous ring
• Cornea

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