Cranial Nerve I Olfactory Nerve Nerve fiber modality: Special sensory afferent Cranial Nerves 1, 5, 7-12 Function: Olfaction Remarkable features: – Peripheral processes act as sensory receptors (the other special sensory nerves have separate Warren L Felton III, MD receptors) Professor and Associate Chair of Clinical – Primary afferent neurons undergo continuous Activities, Department of Neurology replacement throughout life Associate Professor of Ophthalmology – Primary afferent neurons synapse with secondary neurons in the olfactory bulb without synapsing Chair, Division of Neuro-Ophthalmology first in the thalamus (as do all other sensory VCU School of Medicine neurons) – Pathways to cortical areas are entirely ipsilateral 1 2 Crania Nerve I Cranial Nerve I Clinical Testing Pathology Anosmia, hyposmia: loss of or impaired Frequently overlooked in neurologic olfaction examination – 1% of population, 50% of population >60 years Aromatic stimulus placed under each – Note: patients with bilateral anosmia often report nostril with the other nostril occluded, eg impaired taste (ageusia, hypogeusia), though coffee, cloves, or soap taste is normal when tested Note that noxious stimuli such as Dysosmia: disordered olfaction ammonia are not used due to concomitant – Parosmia: distorted olfaction stimulation of CN V – Olfactory hallucination: presence of perceived odor in the absence of odor Quantitative clinical tests are available: • Aura preceding complex partial seizures of eg, University of Pennsylvania Smell temporal lobe origin Identification Test (UPSIT) • Schizophrenia 3 4 Cranial Nerve I Cranial Nerve I Pathology Pathology Nasal passages, Olfactory epithelium, Central Pathways – Nasal: stimuli do not reach olfactory receptors Central pathways: olfactory bulb, •Smoking olfactory tract, central projections • Nasal and paranasal sinus disease: infection (influenza, herpes simplex, hepatitis), allergy, antihistamine – Intracranial tumor: olfactory groove overuse, cocaine – Olfactory epithelium: impairment of receptors or axons meningioma, frontal lobe glioma • Trauma: tearing of epithelium at cribiform plate – 5-10% of head trauma patients have impaired – Aneurysm: anterior cerebral artery olfaction – Degenerative disease: Alzheimer’s, – Note: head trauma causing dural tear may result in CSF rhinorrhea Parkinson’s, Huntington’s • Intranasal tumor: papilloma • Toxic: certain antibiotics (aminoglycosides, tetracycline), • Note: olfaction diminishes with age corticosteroids, opiates, organic solvents 5 6 1 Cranial Nerve V Cranial Nerve V Trigeminal Nerve Three Divisions Nerve Fiber Modalities Ophthalmic branch (V1): superior orbital foramen – Forehead, nose, and anterior scalp to the lateral epicanthus of the eye – Cornea, eye, orbit General sensory afferent – Nasal and frontal sinus mucosa – Function: All general sensory modalities from the: – Dura mater of the falx Maxillary branch (V2): foramen rotundum • Face and anterior scalp – Cheek to the corner of the mouth, sparing the angle of the jaw • Conjunctiva and eye – Upper lip, teeth and gums, and palate – Floor of middle cranial fossa • Paranasal sinuses and nasal cavities Mandibular branch (V3): foramen ovale • Oral cavities, anterior 2/3 of the tongue, and teeth – Sensory •Chin • Part of the external tympanic membrane • Lower lip, teeth, and gums • Meninges of the anterior and middle crania fossae • Anterior 2/3 of tongue • Dura mater above the tentorium Branchial motor efferent –Motor – Function: Innervation of the muscles of mastication Note: brainstem lesions may produce an ‘onion skin’ pattern if sensory loss centering on the nose and lips 7 8 Cranial Nerve V Cranial Nerve V Sensory Clinical Testing Motor Clinical Testing Palpatation of masseter and temporalis Pain (pinprick), touch (cotton swab, light muscles as the patient clenches the teeth finger touch), and temperature (cool tuning Forced jaw opening, closure, and lateral fork) are tested in each of the three divisions movement Note that vibration (tuning fork) is – Note: unilateral CN V motor weakness results in jaw transmitted through the skull and is normally deviation to the ipsilateral side with mouth open appreciated approximately equally on each Jaw (mandibular) jerk: tapping the side of the forehead when unilaterally examiner’s finger placed on the patient’s stimulated chin normally elicits a brisk but slight contraction – Significant asymmetry of vibration is usually – An exaggerated response is a sign of upper motor interpreted as a nonphysiologic response, so called neuron pathology above the foramen magnum ‘splitting’ of vibratory sensation at the forehead – An unelicitable response has little clinical significance 9 10 Cranial Nerve V (and VII) Cranial Nerve V Clinical Testing Pathology Corneal Reflex Supranuclear, Brainstem, – CN V (V1): afferent Preganglionic/Ganglion, Peripheral branches – CN VII: efferent – Supranuclear: ischemia, hemorrhage, neoplasia, – Cotton wisp touched to the cornea unilaterally demyelinating disease, trauma produces a bilateral blink response • Contralateral facial and body sensory loss • A unilateral CN V lesion results in absent – Brainstem: as above, synrinx blink bilaterally with stimulation ipsilateral to • Ipsilateral facial sensory loss the lesion – Preganglionic and gasserion ganglion: • A unilateral CN VII lesion results in absent • tumor (meningioma, schwannoma) blink ipsilateral to the lesion with stimulation • inflammation (sarcoid) of either cornea • infection (bacterial, fungal, mycobacterial) 11 12 2 Cranial Nerve V Cranial Nerve V Pathology Pathology Peripheral branches Trigeminal Neuralgia (Tic deloureux) – Infection: – The most common neuralgia • Herpes zoster • Approximately 4 per 100,000; women to men 3:2 – Symptoms: – Usually V1: acute herpetic eruption and pain • Paroxysms of extremely severe pain in one or more of the divisions of the trigeminal nerve, usually V2 or V3 – May result in post-herpetic neuralgia: burning, • Pain is typically lancinating, lasting a few seconds aching, or lancinating; mild sensory loss; • Pain may occur spontaneously or be triggered by touch, eating, aggravated by touch or talking • Sensory testing of CN V is usually normal – May result in corneal damage and visual loss –Pathology • Other: bacterial, fungal • Usually of unknown etiology • May be due to compression by a tortuous blood vessel – Inflammation: sarcoid, Sjogren’s syndrome, SLE • May be a symptom of multiple sclerosis – Tumor: sinus tumor, lymphoma, skin cancer, metastasis – Treatment • Medication: anticonvulsants (eg carbamazepine, gabapentin) –Trauma • Less commonly, surgery 13 14 Cranial Nerve VII Cranial Nerve VII Facial Nerve Clinical Testing Nerve Fiber Modalities Muscles of Facial Expression Branchial motor efferent Observation of the patient’s facial expression – Function: Innervate the muscles of facial expression, plus when relaxed and when speaking stapedius, stylohyoid, and posterior belly of digastric Observation when the patient is asked to Visceral motor (parasympathetic) efferents wrinkle the forehead, smile, forcibly close the – Function: Stimulation of the lacrimal, submandibular, and eyes, puff the cheeks, and contract the sublingual glands, and mucous membranes of the nose and hard and soft palates platysma General sensory afferent Weakness is demonstrated by facial – Function: General sensation from the concha of the auricle, asymmetry, diminished nasolabial fold, possibly the external auditory meatus, and part of the external widened palpebral fissure, reduced forehead tympanic membrane wrinkling, impaired smile, and inability to Special sensory afferent puff out the cheeks – Function: Taste sensation from the anterior 2/3 of the tongue Corneal reflex (see CN V) 15 16 Cranial Nerve VII Cranial Nerve VII Upper and Lower Motor Neuron Clinical Testing Lesions Taste Upper motor neuron lesions: contralateral deficit – Frontalis and obicularis oculi muscles are spared due to bilateral motor cortex input to the part of the facial nucleus supplying Tested using a moist cotton swab these muscles dipped into sweet, sour, or salty – Loss of lower facial motor voluntary expression contralateral to the CNS lesion due to unilateral input to the part of the facial preparations nucleus supplying these muscles – Note: Facial motor emotional expression is sometimes The patient protrudes the tongue, the preserved as the corresponding neuronal input follows a different pathway cotton swab is applied unilaterally, and Lower motor neuron lesions: ipsilateral deficit the patient is asked to identify the taste – Both upper and lower muscles of facial expression are affected ipsilateral to the lesion without retracting the tongue – Note: Taste is affected if the lesion is proximal to the chorda tympani and spared if the lesion is distal to this nerve 17 18 3 Cranial Nerve VII Cranial Nerve VII Pathology Pathology – Peripheral Nerve Upper Motor Neuron, Brainstem, • Facial canal: facial weakness, loss of taste (if lesion proximal to chorda tympani), variably hyperacusis (if Peripheral Nerve lesion proximal to nerve to stapedius), and decreased – Upper motor neuron/central facial palsy: lacrimation and salivation (if lesion proximal to greater superficial petrosal nerve) ischemia, hemorrhage, tumor, trauma, – Bell’s palsy infection, demyelination – Tumor: cholesteatoma, hemangioma • Contralateral lower facial and extremity –Trauma weakness • Stylomastoid foramen: facial weakness in isolation –Trauma – Brainstem: ischemia, hemorrhage,