Afferent fibers of cranial nerves enter the central nervous system (CNS) and terminate in relation to aggregates of neurons in sensory nuclei. Motor or efferent components of cranial nerves arise from motor nuclei. All motor and sensory nuclei that contribute fibers to cranial nerves are organized in a series of discontinuous columns according to the functional component that they contain. Motor nuclei are situated medially, closest to the midline, and sensory nuclei are situated lateral to the motor nuclei. A cranial nerve nucleus or nerve will be found at virtually every transverse sectional level of the brain stem (Figure III-5-4).
| CN | Name | Type | Function | Results of Lesions |
|---|---|---|---|---|
| I | Olfactory | Sensory | Smells | Anosmia |
| II | Optic | Sensory | Sees | Visual field deficits (anopsia) Loss of light reflex with III Only nerve to be affected by MS |
| III | Oculomotor | Motor | Innervates SR, IR, MR, IO extraocular muscles: adduction (MR) most important action Raises eyelid (levator palpebrae superioris) Constricts pupil (sphincter pupillae) Accommodates (ciliary muscle) | Diplopia, external strabismus Loss of parallel gaze Ptosis Dilated pupil, loss of light reflex with II Loss of near response |
| IV | Trochlear | Motor | Superior oblique—depresses and abducts eyeball (makes eyeball look down and out) Intorts | Weakness looking down with adducted eye Trouble going down stairs Head tilts away from lesioned side |
| V | Trigeminal
| Mixed | General sensation (touch, pain, temperature) of forehead/scalp/cornea General sensation of palate, nasal cavity, maxillary face, maxillary teeth General sensation of anterior two-thirds of tongue, mandibular face, mandibular teeth Motor to muscles of mastication (temporalis, masseter, medial and lateral pterygoids) and anterior belly of digastric, mylohyoid, tensor tympani, tensor palati | V1—loss of general sensation in skin of forehead/scalp Loss of blink reflex with VII V2—loss of general sensation in skin over maxilla, maxillary teeth V3—loss of general sensation in skin over mandible, mandibular teeth, tongue, weakness in chewing Jaw deviation toward weak side Trigeminal neuralgia—intractable pain in V2 or V3 territory |
| VI | Abducens | Motor | Lateral rectus—abducts eyeball | Diplopia, internal strabismus Loss of parallel gaze, “pseudoptosis” |
| VII | Facial | Mixed | To muscles of facial expression, posterior belly of digastric, stylohyoid, stapedius Salivation (submandibular, sublingual glands) Skin behind ear Taste in anterior
Tears (lacrimal gland) | Corner of mouth droops, cannot close eye, cannot wrinkle forehead, loss of blink reflex, hyperacusis; Bell palsy—lesion of nerve in facial canal Pain behind ear Alteration or loss of taste (ageusia) Eye dry and red |
| VIII | Vestibulocochlear | Sensory | Hearing Angular acceleration (head turning) Linear acceleration (gravity) | Sensorineural hearing loss Loss of balance, nystagmus |
| IX | Glossopharyngeal | Mixed | Oropharynx sensation, carotid sinus/body Salivation (parotid gland) All sensation of posterior one-third of tongue Motor to one muscle—stylopharyngeus | Loss of gag reflex with X |
| X | Vagus | Mixed | To muscles of palate and pharynx for swallowing except tensor palati (V) and stylopharyngeus (IX) To all muscles of larynx (phonates) Sensory of larynx and laryngopharynx Sensory of GI tract To GI tract smooth muscle and glands in foregut and midgut | Nasal speech, nasal regurgitation Dysphagia, palate droop Uvula pointing away from affected side Hoarseness/fixed vocal cord Loss of gag reflex with IX Loss of cough reflex |
| XI | Accessory | Motor | Head rotation to opposite side (sternocleidomastoid) Elevates and rotates scapula (trapezius) | Weakness turning chin to opposite side Shoulder droop |
| XII | Hypoglossal | Motor | Tongue movement (styloglossus, hyoglossus, genioglossus, and intrinsic tongue muscles—palatoglossus is by X) | Tongue pointing toward same (affected) side on protrusion |
| Abbreviations: CN, cranial nerve; IO, inferior oblique; IR, inferior rectus; MR, medial rectus; MS, multiple sclerosis; SR, superior rectus | ||||
of tongue/palate 
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