Accessory Nerve Flashcards

Explore the accessory nerve's spinal origin, cranial connections, skull passage, muscular innervation, neck relationships, and clinical lesions.

Card 1 of 30Question

What is the numerical designation of the accessory nerve?

Cranial nerve XI (CN XI).

In This Section

1. What is the numerical designation of the accessory nerve?

Cranial nerve XI (CN XI).

2. What is the primary function of the spinal accessory nerve?

Motor innervation of the sternocleidomastoid and trapezius muscles.

3. Where is the spinal accessory nucleus located?

In the ventral horn region of the upper cervical spinal cord, approximately at segments C1 to C5.

4. From which region do the spinal rootlets of the accessory nerve emerge?

The lateral surface of the upper cervical spinal cord, between the dorsal and ventral spinal roots.

5. Through which opening do the spinal accessory nerve rootlets enter the cranial cavity?

The foramen magnum.

6. Through which skull opening does the accessory nerve exit the cranial cavity?

The jugular foramen.

7. Which other cranial nerves exit the skull through the jugular foramen?

The glossopharyngeal nerve (IX) and vagus nerve (X).

8. Which medullary nucleus is traditionally associated with the cranial root of the accessory nerve?

The nucleus ambiguus.

9. How is the traditional cranial root of the accessory nerve classified in modern anatomical descriptions?

It is generally considered part of the vagus nerve rather than the accessory nerve proper.

10. Which muscles receive fibers traditionally attributed to the cranial accessory root?

Muscles of the pharynx and larynx through branches of the vagus nerve.

11. Which two muscles receive direct motor innervation from the spinal accessory nerve?

The sternocleidomastoid and trapezius muscles.

12. What is the relationship of the accessory nerve to the sternocleidomastoid muscle?

It typically enters the deep surface of the muscle and passes through or beneath it.

13. Which anatomical triangle does the accessory nerve cross after emerging from the sternocleidomastoid?

The posterior triangle of the neck.

14. What is the relationship of the accessory nerve to the investing layer of deep cervical fascia in the posterior triangle?

It courses through the posterior triangle deep to the investing layer of deep cervical fascia.

15. Which muscle does the accessory nerve enter after crossing the posterior triangle?

The trapezius muscle, usually through its deep surface.

16. Why is the accessory nerve vulnerable during surgery in the posterior triangle of the neck?

Its relatively superficial course makes it susceptible to injury during lymph node biopsy or neck dissection.

17. Which cervical spinal nerves contribute proprioceptive fibers associated with the sternocleidomastoid?

Primarily the second and third cervical spinal nerves (C2 and C3).

18. Which cervical spinal nerves contribute sensory and proprioceptive fibers associated with the trapezius?

Primarily the third and fourth cervical spinal nerves (C3 and C4).

19. What is the principal action of one sternocleidomastoid muscle during unilateral contraction?

Rotation of the face toward the opposite side, with ipsilateral lateral flexion of the neck.

20. What movement is produced by bilateral contraction of the sternocleidomastoid muscles?

Flexion of the cervical spine, with effects on head position depending on posture.

21. What are the major actions of the trapezius muscle?

Elevation, retraction, depression, and upward rotation of the scapula, depending on the fibers activated.

22. Which trapezius fibers are primarily responsible for elevating the shoulder?

The superior fibers of the trapezius.

23. How does trapezius weakness affect overhead arm elevation?

It impairs upward rotation of the scapula, making full overhead elevation difficult.

24. What is a characteristic shoulder finding in unilateral accessory nerve palsy?

Drooping of the ipsilateral shoulder due to trapezius weakness.

25. What movement is weakened by injury to the accessory nerve supplying the sternocleidomastoid?

Rotation of the head toward the side opposite the affected muscle.

26. How is the sternocleidomastoid component of accessory nerve function tested?

By asking the patient to turn the head against resistance while palpating the opposite sternocleidomastoid.

27. How is trapezius function assessed during a cranial nerve examination?

By asking the patient to shrug the shoulders against resistance.

28. What scapular abnormality may result from accessory nerve injury?

Lateral scapular winging or abnormal scapular positioning caused by trapezius weakness.

29. How does accessory nerve injury differ from long thoracic nerve injury?

Accessory nerve injury weakens the trapezius, while long thoracic nerve injury weakens the serratus anterior.

30. Which skull base syndrome can affect the accessory nerve together with cranial nerves IX and X?

Jugular foramen syndrome, also called Vernet syndrome.