The 5th cranial nerve, also known as the trigeminal nerve, is responsible for sensation in the face and certain motor functions like chewing. Testing the integrity and function of this nerve is an important part of the neurological exam. There are several quick clinical tests that can be done to assess the 5th cranial nerve.
Anatomy and Function
The trigeminal nerve is the largest cranial nerve. It has three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3).
- V1 provides sensation to the forehead, eye, nose and upper cheek.
- V2 provides sensation to the midface including the upper lip, upper teeth, lower eyelid, side of nose and cheek.
- V3 provides sensation to the lower lip, chin, lower teeth and side of the mouth. It also controls the muscles used for chewing.
Testing the three branches of the trigeminal nerve allows assessment of both sensory and motor function.
Equipment Needed
Testing the trigeminal nerve requires minimal equipment:
- Cotton wisp or cotton tip applicator
- Tongue depressor
- Alcohol swab
- Tuning fork (128Hz)
- Pin, paperclip or safety pin
Sensory Testing
The main sensory modalities to test for each branch are:
- Light touch – using a cotton wisp or cotton tip applicator
- Pinprick/pain – using a safety pin, pin or paperclip
- Temperature – using a cool alcohol swab
- Vibration – using a 128Hz tuning fork
For light touch, stroke the cotton wisp across the skin in each division of the trigeminal nerve. Compare side to side, assessing if the patient can feel the light touch equally on both sides of the face.
For pinprick/pain, lightly poke the skin in each division, comparing side to side. Make sure not to break the skin.
For temperature, touch the cool alcohol swab to the skin and ask if it feels cooler compared to the other side of the face without the swab.
For vibration sense, place the tuning fork on the facial bones such as the brow or cheek bone. The patient should feel the buzzing/vibrating sensation equally on both sides.
Ophthalmic Nerve (V1)
Test sensation on the forehead, eyebrow, eyelid, and side of the nose.
Maxillary Nerve (V2)
Test sensation on the cheek, upper lip, gums, teeth, side of the nose and lower eyelid.
Mandibular Nerve (V3)
Test sensation on the jaw, lower lip, chin, tongue, teeth and side of the mouth.
Motor Testing
Motor function of the trigeminal nerve involves the muscles of mastication (chewing). This is supplied by V3, the mandibular branch.
Have the patient clench their teeth and palpate the masseter muscle on each side. It should contract equally on both sides. Test jaw strength by having the patient gently bite down on a tongue depressor as you try to remove it from their mouth. Strength should be equal on both sides.
Corneal Reflex
Another quick test of the trigeminal nerve is the corneal reflex. This tests the afferent and efferent pathways of the ophthalmic branch (V1).
Lightly touch the cornea with a wisp of cotton. There should be an immediate bilateral blink response. If absent or decreased on one side, it can indicate dysfunction of V1.
Summary of Clinical Testing
| Nerve Branch | Sensory Modalities | Motor Function |
|---|---|---|
| Ophthalmic (V1) | Light touch, pinprick, temperature | Corneal reflex |
| Maxillary (V2) | Light touch, pinprick, temperature | – |
| Mandibular (V3) | Light touch, pinprick, temperature, vibration sense | Jaw clenching, biting strength |
Interpreting Abnormal Findings
If any abnormalities are found on testing the trigeminal nerve, it can indicate various pathologies depending on the location.
- Forehead/Eye (V1) – May indicate an intracranial mass compressing the nerve, stroke, Multiple Sclerosis
- Cheek/Nose (V2) – May indicate infraorbital nerve damage, sinus pathology
- Jaw (V3) – May indicate mandibular nerve pathology, temporomandibular joint dysfunction
- Multiple Branches – May indicate nerve damage from trauma, infections like shingles, tumors, neuropathy (e.g. diabetes)
Careful testing of the trigeminal nerve during a neurological exam can pick up subtle findings that give clues towards a diagnosis.
Conclusion
Testing the 5th cranial nerve or trigeminal nerve evaluates both sensory and motor function of the face. Quick clinical tests include assessing light touch, pinprick, vibration sense and the corneal reflex. Abnormal findings can indicate issues with the nerve itself or point towards underlying neurologic conditions.
Careful examination of the three branches of the trigeminal nerve – ophthalmic, maxillary and mandibular – is an essential component of the neurological exam and can provide valuable diagnostic information.
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