Cranial nerve function The cranial nerves have sensory functions, including vision, smell, hearing, taste, and facial sensations. The also contribute to eye movement; head, neck, and shoulder function; and jaw, tongue, and throat functions such as speech, swallowing, and gagging. As such, some of the cranial nerves have motor functions, some have sensory functions, and some have both (Taylor et al., 2021). Testing the cranial nerves The cranial nerves can be tested easily and quickly in the clinic as follows. Smell and hearing Cranial nerve I, olfactory nerve: Ask the patient to close their eyes and one nostril, introduce a familiar smell (a Sharpie marker works well in the clinic), and ask them to identify it. Repeat on the opposite side and note any side-to-side differences. Cranial nerve VIII, vestibulocochlear nerve: Rub your fingers near each of the patient’s ears and note any side-to-side differences. Eyes Cranial nerve II, optic nerve: Ask the patient to cover one eye. Then bring a pen or finger in from four directions diagonally toward the center of the visual field. The patient reports when the pen/finger becomes detectable and any visual field cuts are noted. Cranial nerve III, oculomotor nerve: Ask the patient to outstretch their arm and raise their index finger. Now have them move the finger toward their nose, following it with their eyes (accommodation or convergence). Side-to-side differences should be noted. Cranial nerves III, IV, and VI, oculomotor, trochlear, and abducens nerves: Move a pen in an H pattern 30 to 40 cm in front of the patient. Ask the patient to follow the target without moving their head. Observe the eyes for symmetry of movement, deviations, lag, or nystagmus. Face, jaw, throat, and tongue Cranial nerve V, trigeminal nerve (sensory): Using a cotton ball, stroke the client’s skin along the ophthalmic division (scalp, forehead, upper eyelid) and mandibular division (chin, jaw, lower lip). Note any side-to-side differences. Cranial nerve V, trigeminal nerve (motor): Examine the function of the temporalis, masseteric, and pterygoid muscles by palpating the masseter muscles while the patient clenches their teeth and then asking them to open their mouth against resistance. If the pterygoid is weak, the jaw deviates to the side when the mouth is opened. Differential diagnosis cervical conditions When systemic and viscerogenic sources of neck pain have been ruled out, the task facing the assessing clinician is to determine what cervical structure(s) are causing the client’s presenting symptoms. This is absolutely necessary for determining an effect treatment plan. Facet joint pain Facet (or zygapophyseal) joint dysfunction is a possible source of neck pain. According to Hurley et al. (2022), the facet joints are considered the primary source of pain in 26%–70% of patients with chronic neck pain and 54%–60% of neck pain following whiplash injury. The C2–C3 and C5– C6 joints are most commonly implicated in neck pain, with C2–C3, C3–C4, and C4–C5 being the most radiologically involved (Hurley et al., 2022).
Cranial nerve VII, facial nerve: Ask the patient to smile, frown, raise their eyebrows, and puff out their cheeks while you check for symmetry. Cranial nerve IX, glossopharyngeal nerve: Touching a tongue depressor gently to the back of the throat on one side to test the ipsilateral gage reflex can be used to assess for unilateral lesion in the glossopharyngeal nerve. Cranial nerve X, vagus nerve: Ask the patient to open their mouth and say “aaaaahhhhhh” while you observe for symmetrical elevation of the soft palate and central ascent of the uvula. Cranial nerve XII, hypoglossal nerve: Ask the client to stick out their tongue, and move it side to side. Head, neck, and shoulder Cranial nerve XI, accessory nerve: Ask the client to resist shrugging of the shoulder. When examination reveals side-to-side differences or abnormal responses, this may be an indication to refer the patient to another healthcare provider for further examination or appropriate imaging/testing. The urgency of referral depends on the full clinical picture in terms of the client’s status and symptoms. According to Taylor et al. (2021), the diagnostic accuracy of a complete cranial nerve examination is moderate at best. However, cranial nerve dysfunction may link to a wide variety and combination of potential pathologies, and a thorough medical screening during physical therapy examination for neck pain and headaches should include this element. At present, Mourad et al. (2021) report that physical therapists only rarely or occasionally perform a cranial nerve examination, so this is an area in need of improvement. Self-Assessment Quiz Question #31 Which two cranial nerves are involved in smell and hearing? a. Vagus and hypoglossal nerves. Self-Assessment Quiz Question #32 The cranial nerve that can be tested by resisting the client’s ability to shrug the shoulders is: a. Cranial nerve X, the hypoglossal nerve. b. Cranial nerve XI, the accessory nerve. c. Cranial nerve V, the trigeminal nerve. d. Cranial nerve XII, the hypoglossal nerve. Healthcare consideration: Since research shows that the facet joints are frequently involved in both acute and chronic neck pain, physical therapists must be skilled at differentiating whether the facet joints are involved. Three ways to assess facet joint function are (1) looking at deficits in neck flexion, side bend, and rotation as each of the facet joints contributes their part to overall cervical motion; (2) observing the neck during flexion, rotation, and side bend to see if there is a visible restriction in motion at any particular level; and (3) providing posteroanterior pressure to each level of the cervical spine on both sides to determine if there is stiffness/decreased motion or pain at any level. b. Facial and glossopharyngeal nerves. c. Olfactory and vestibulocochlear nerves. d. Trigeminal and oculomotor nerves.
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