Nerve
Accessory nerve (CN XI)
Trapezius and sternocleidomastoid
High-yield
Purely motor to SCM and trapezius; vulnerable in the posterior triangle of the neck → shoulder droop and weak head turning.
Overview
The eleventh cranial nerve, supplying the sternocleidomastoid and trapezius via its spinal root that ascends into the skull and re-exits.
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Reference facts
- Roots
- Motor (spinal root C1-C5/C6)
- Course
- The spinal root ascends through the foramen magnum, joins the cranial root briefly, exits the jugular foramen, and crosses the posterior triangle of the neck
- Motor
- Sternocleidomastoid and trapezius
- Sensory
- No cutaneous sensory territory - this nerve is purely motor.
Clinical correlation
Iatrogenic injury during lymph node biopsy in the posterior triangle causes trapezius weakness and shoulder droop.
Frequently asked questions
What are the roots of the accessory nerve (CN XI)?
The accessory nerve (CN XI) arises from motor (spinal root C1-C5/C6).
What muscles does the accessory nerve (CN XI) supply?
The accessory nerve (CN XI) supplies the sternocleidomastoid and trapezius.
What is the sensory distribution of the accessory nerve (CN XI)?
No cutaneous sensory territory - this nerve is purely motor.
What is the course of the accessory nerve (CN XI)?
The spinal root ascends through the foramen magnum, joins the cranial root briefly, exits the jugular foramen, and crosses the posterior triangle of the neck.