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Cranial Nerves VII-XII Quiz
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Which finding is most consistent with a unilateral lesion of the hypoglossal nerve?
- A Tongue deviates towards the side of the lesion on protrusion You picked ✓
- B Inability to shrug the shoulders against resistance You picked ✕
- C Hoarse voice with a paralysed vocal cord You picked ✕
- D Loss of gag reflex with preserved tongue movements You picked ✕
- E Loss of taste sensation from the anterior two-thirds of the tongue You picked ✕
Correct!
Incorrect
The answer is A: Tongue deviates towards the side of the lesion on protrusion
Explanation
Why A is correct
See Cranial Nerve X. Vagus. Option A is correct: the hypoglossal nerve (cranial nerve XII) is purely a motor nerve that supplies all the extrinsic and intrinsic muscles of the tongue, apart from the palatoglossus, which is supplied by the vagus nerve. The extrinsic muscles (such as the genioglossus, hyoglossus and styloglossus) move the tongue as a whole, and the intrinsic muscles change its shape. To test the nerve, the patient is asked to stick out the tongue. In a lower motor neurone (peripheral) lesion the muscles on the damaged side are weak, so the tongue deviates towards the damaged side on protrusion, and there may also be wasting and fasciculations (small visible twitches of muscle fibres) on the affected side. A simple memory aid, widely used by students: the tongue licks its wounds, so it points to the side of the lesion.
- Nerve: the hypoglossal nerve (cranial nerve XII) is purely motor.
- Supply: it supplies all the extrinsic and intrinsic muscles of the tongue except the palatoglossus, which the vagus nerve supplies.
- Lesion: in a lower motor neurone lesion the tongue deviates towards the damaged side on protrusion, with possible wasting and fasciculations.
Why the other options are incorrect
- B. Inability to shrug the shoulders against resistance: Shoulder shrugging is powered by the trapezius, which is supplied by the accessory nerve. It would be the answer if the question asked about a lesion of cranial nerve XI. Your answer
- C. Hoarse voice with a paralysed vocal cord: A hoarse voice with a paralysed vocal cord points to the recurrent laryngeal branch of the vagus nerve. The vagus supplies the muscles of the larynx, whereas the hypoglossal supplies the tongue. Your answer
- D. Loss of gag reflex with preserved tongue movements: The sensory limb of the gag reflex depends on the glossopharyngeal nerve, not the hypoglossal nerve. A lesion of the glossopharyngeal nerve would leave the tongue moving normally, which is why this is not the answer. Your answer
- E. Loss of taste sensation from the anterior two-thirds of the tongue: Taste from the front of the tongue travels in the chorda tympani, a branch of the facial nerve. The hypoglossal nerve is purely motor, so it carries no taste or sensation. Your answer
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More questions from this set. Start the quiz to answer them and see each explanation.
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1
Which muscle is innervated by the glossopharyngeal nerve and helps with swallowing?
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2
Which function is mainly carried out by the vestibular part of the vestibulocochlear nerve?
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