Trigeminal Nerve | Cranial Nerve V / CN V Assessment

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Trigeminal Nerve | Cranial Nerve V / CN V Assessment

The trigeminal nerves sensory nucleus has three branches:

the ophthalmic division innervating the skin of the forehead and the cornea and conjunctiva
the maxillary division innervating the skin in the middle of the face
and the mandibular division supplying sensory innervation to the skin of the lower jaw and motor fibers to the muscles of mastication namely the temporalis, masseter and pterygoids

Sensory Function

To test the sensory innervation, a cotton wool ball and blunt pin are used. The patient is asked to close their eyes. Then the cotton ball and pin sequentially touch the forehead, the malar eminence, and the lower face over the mandible. The patient is asked to state when they feel the touch and whether they feel a sharp or dull sensation. Both sides are compared.

Another item to test is the corneal reflex. Stand to the side of the patient and depress the patient’s eyelid. Ask them to gaze into the distance. Then using a wisp of cotton, touch the cornea gently. Ask the patient whether they felt touching of the cornea and observe for a blinking reflex in both eyes.

Motor Function

To test the motor function of the mandibular division ask the patient to clench the jaw while you palpate for muscle tone and muscle bulk. You can also ask the patient to hold the mouth open while you try to force it shut with your hands.

At last examine for an exaggerated jaw reflex. Place one index finger on the chin and tap it with your reflex hammer. Normally you would observe slight closure or no reflex at all.