An assessment of the cranial nerves will provide information regarding the central nervous system and serves as a triage for identifying lesions or dysfunction at the level of the CNS.
- 1. CN 1: The olfactory nerve can be tested using products with specific spices, so the patient recognizes the differences; however, usually just asking the patient: “Do you recognize different aromas?” is enough.
- 2. CN 2: Has several elements that can be tested. In this abbreviated exam, we will test only reflex response for the direct and concentric reflex to bright light. This is done by shining a pen torch into one eye and checking that the pupils on both sides constrict. This should be tested on both sides.
- 3. CN 3, 4, and 6: These 3 nerves (oculomotor, trochlear, and abducens) are tested together as the control movement of the eye. This is done by asking the patient to keep their head perfectly still directly in front of you; you should draw two large joining H’s in front of them using your finger and ask them to follow your finger with their eyes.
- 4. CN 5 (trigeminal – motor) to test the motor supply of this nerve ask the patient to clench their teeth together, observing and feeling the bulk of the masseter and temporalis muscles. Ask the patient to open against resistance.
- 5. CN 5 (trigeminal nerve – sensory) provides sensory supply to the face and mouth. It has three sensory branches (ophthalmic, maxillary, and mandibular) and it is tested by lightly touching the face with a piece of cotton wool followed by a blunt pin in each division on each side of the face. The corneal or blink reflex should also be examined as the sensory supply to the cornea is from this nerve. Do this by lightly touching the cornea with cotton wool, which causes the patient to shut both eyelids.
- 6. CN 7: Facial motor nerve supplies motor branches to the muscles of facial expression. This nerve is therefore tested by asking the patient to crease up their forehead (raise their eyebrows), close their eyes and keep them closed against resistance, puff out their cheeks and reveal their teeth.
- 7. CN 8: the vestibulocochlear nerve provides innervation to the hearing apparatus of the ear and can be used to differentiate conductive and sensory-neural hearing loss using the Rinne and Weber tests.
- a. WEBER: place the tuning fork base down in the center of the patient’s forehead and ask if it is louder in either ear. Normally it should be heard equally in both ears.
- b. RINNE: place a sounding tuning fork on the mastoid process and then next to their ear and ask which is louder (normally the second is louder).
- 8. CN 9: Glossopharyngeal nerve provides sensory supply to the palate. It can be tested with the gag reflex or by touching the arches of the pharynx.
- 9. CN 10: Vagus nerve provides motor supply to the pharynx. The test is done by asking the patient to say “AH” which causes it to elevate. Observe the position of the uvula, as it is centrally located and does not deviate on movement.
- 10. CN 11: The accessory nerve gives motor supply to the SCM and trapezius muscles. Ask the patient to shrug their shoulders and turn their head against resistance.
- 11. CN 12: The hypoglossal nerve provides motor supply to the muscles of the tongue. Check for fasciculation at rest and ask the patient to stick their tongue out. If the tongue deviates to either side, it suggests a weakening of the muscles on that side.
- 12. Once the examination is concluded, dispose of the sharps and gloves accordingly with the standard biosecurity measurements. Explain to the patient any inconsistent or irregular findings and refer if appropriate.
Some of the possible findings or conditions this test might identify are:
- CN 1: The olfactory is a sensory nerve; damage in the nasal epithelium or the basal ganglia might impair the ability to discriminate different smells.
- CN 2: Optic is also a sensory nerve. The POSSIBLE FINDINGS include neuritis (related to loss of myelin), glaucoma, and autoimmune conditions.
- CN 3, 4 & 6: When the patient cannot track motion this means neurologic damage involving cranial nerves 3, 4, or 6. The POSSIBLE FINDINGS [e.g. brain tumor, hemorrhagic brain disease, stroke, local eye disease damaging the muscles of ocular motion].
- CN 5 (Tactile testing): Tactile stimulation is a test of trigeminal nerve function (A-beta fibers) and POSSIBLE FINDINGS [multiple sclerosis, toxic neuropathy, diabetes, nerve trauma, neural invasion carcinoma]
- CN 5 (Motor function testing): The eight muscles, which the trigeminal motor nerve innervates: masseter, temporalis, medial pterygoid, lateral pterygoid, mylohyoid, tensor tympani, tensor veli palatine, and anterior belly of digastric.
- CN 5 (Corneal Reflex Testing): The corneal or blink reflex has two parts, the ophthalmic branch of the trigeminal nerve mediates the sensory or afferent part of the reflex and the motor or efferent part of the reflex is mediated by the facial nerve.
- CN 5 (Dermatome of V1, V2 & V3): The sensory nerve distributions of the trigeminal nerve on the face which are: (a) Ophthalmic division: the forehead, upper eyelid, cornea, conjunctiva, and dorsum of the nose; (b) Maxillary division: the upper lip, lateral portions of nose, upper cheek, anterior temple, mucosa of the nose, upper jaw, upper teeth, and roof of the mouth; (c) Mandibular division: the lower lip, chin, posterior cheek, temple, external ear, mucosa of the lower part of the mouth, and anterior two-thirds of the tongue and it does not include the angle of mandible!!
a.uth.tmc.edu/neuroscience/m/s3/chapter07.html