Sun28November0333PM 45

A 24-year-old man with severe traumatic brain injury has his gag reflex assessed as part of brain stem death testing.

Which one of the following nerves forms the afferent limb of this reflex arc?

(Please select 1 option)

Vagus nerve

Accessory nerve

Glossopharyngeal nerve Correct

Hypoglossal nerve

Trigeminal nerve

Explanation

The gag reflex prevents the passage of material into the aerodigestive tract except during swallowing. It comprises elevation of the soft palate and contraction of the pharyngeal muscles in response to stimulation of the posterior pharyngeal wall.

As with all reflexes, the gag reflex has afferent (sensory) and efferent (motor) limbs. The glossopharyngeal nerve forms the afferent limb and the vagus nerve the efferent.

Unilateral stimulation of the pharynx ordinarily elicits a consensual (bilateral) motor response. In unilateral glossopharyngeal nerve damage, there will be no gag reflex elicited on touching the affected side. Unilateral injury to the vagus nerve causes the soft palate to elevate and deviate toward the intact side when either side of the pharynx is stimulated.

If both the glossopharyngeal and vagus nerves are damaged on one side, then stimulation of the normal side elicits a unilateral response with deviation of the soft palate toward that side, whereas touching the damaged side produces no response at all.

Answer Statistics

1

17%

2

2%

3

75%

4

7%

5

2%

Times answered: 256