Hypoglossal Nerve Flashcards

Study the hypoglossal nerve's medullary origin, skull exit, cervical course, tongue muscle innervation, motor functions, and clinical lesions.

Card 1 of 30Question

What is the numerical designation of the hypoglossal nerve?

Cranial nerve XII (CN XII).

In This Section

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

Cranial nerve XII (CN XII).

2. What is the functional classification of the hypoglossal nerve?

General somatic efferent (GSE), carrying somatic motor fibers.

3. What is the primary function of the hypoglossal nerve?

Motor innervation of the intrinsic and most extrinsic muscles of the tongue.

4. Where is the hypoglossal nucleus located?

In the dorsomedial medulla oblongata, near the midline beneath the floor of the fourth ventricle.

5. Which surface landmark of the fourth ventricle overlies the hypoglossal nucleus?

The hypoglossal trigone.

6. From which sulcus of the medulla do hypoglossal nerve rootlets emerge?

The preolivary sulcus, between the pyramid and olive.

7. Through which skull opening does the hypoglossal nerve leave the cranial cavity?

The hypoglossal canal of the occipital bone.

8. What is the relationship of the hypoglossal nerve to the internal carotid artery and internal jugular vein near the skull base?

It descends in the interval between these vessels after leaving the hypoglossal canal.

9. Which major artery does the hypoglossal nerve cross as it curves forward in the neck?

The external carotid artery.

10. Which muscle does the hypoglossal nerve pass deep to as it approaches the tongue?

The posterior belly of the digastric muscle.

11. What is the relationship of the hypoglossal nerve to the hyoglossus muscle?

It courses superficial to the hyoglossus muscle as it enters the tongue.

12. Which extrinsic tongue muscles are directly innervated by the hypoglossal nerve?

The genioglossus, hyoglossus, and styloglossus muscles.

13. Which extrinsic tongue muscle is not innervated by the hypoglossal nerve?

The palatoglossus muscle, supplied by the vagus nerve through the pharyngeal plexus.

14. Which intrinsic tongue muscles receive hypoglossal motor innervation?

The superior longitudinal, inferior longitudinal, transverse, and vertical tongue muscles.

15. What is the main action of the genioglossus muscle?

Protrusion of the tongue, with unilateral contraction deviating it toward the opposite side.

16. What is the primary action of the hyoglossus muscle?

Depression of the tongue.

17. What is the primary action of the styloglossus muscle?

Retraction and elevation of the tongue.

18. What is the main function of the intrinsic tongue muscles?

Changing the shape of the tongue by shortening, lengthening, curling, and flattening it.

19. Which cervical spinal nerve fibers briefly travel with the hypoglossal nerve?

Primarily fibers from the first cervical spinal nerve (C1).

20. Which two muscles receive C1 motor fibers carried temporarily by the hypoglossal nerve?

The geniohyoid and thyrohyoid muscles.

21. Which root of the ansa cervicalis is formed mainly by C1 fibers traveling briefly with the hypoglossal nerve?

The superior root of the ansa cervicalis.

22. Do C1 fibers traveling with the hypoglossal nerve originate from the hypoglossal nucleus?

No. They originate from cervical spinal motor neurons and temporarily accompany cranial nerve XII.

23. What happens to tongue position during protrusion after a unilateral lower motor neuron hypoglossal lesion?

The tongue deviates toward the affected side.

24. Why does the tongue deviate toward the affected side in unilateral hypoglossal nerve palsy?

The intact contralateral genioglossus pushes the tongue toward the weakened side.

25. What happens to tongue muscle bulk after a chronic lower motor neuron hypoglossal lesion?

The ipsilateral tongue muscles develop atrophy, often accompanied by fasciculations.

26. How does a unilateral supranuclear lesion typically affect tongue protrusion?

The tongue usually deviates away from the side of the cerebral lesion, without marked denervation atrophy.

27. Which medullary vascular syndrome can cause ipsilateral hypoglossal weakness with contralateral limb weakness?

Medial medullary syndrome, also called Dejerine syndrome.

28. Which skull base region may compress the hypoglossal nerve and cause tongue weakness?

The hypoglossal canal, where tumors or other lesions can affect the nerve.

29. How is hypoglossal nerve motor function commonly examined?

By observing the tongue at rest and during protrusion, lateral movement, and movement against cheek resistance.

30. Which functions may be impaired by bilateral hypoglossal nerve paralysis?

Tongue movement during speech, chewing, swallowing, and maintenance of upper airway patency.