Cranial Nerves Nestor T. Hilvano, M.D., M.P.H.

Learning Objectives Locate cranial nerves and describe its pathway, innervations and functions. Identify common injuries associated with cranial nerves. Discuss the following cranial reflexes. a. corneal reflex b. light reflex

Cranial Nerves 12 pair of nerves arise from brain exit through foramina leading to muscles, glands and sense organs in head and neck Which cranial nerves are purely sensory? Purely Motor? Mixed?

Cranial Nerves Olfactory Nerve (CN I)- arises at telencephalon; special sensory for smell; damage results to anosmia Optic Nerve (CN II)- arises at diencephalon; special sensory for vision; damage results to anopsia Oculomotor Nerve (CN III)- arises at ventral surface of midbrain; Motor- somatic motor to extrinsic muscles for eyes (except superior oblique and lateral rectus), and visceral motor (autonomic) via ciliary ganglion to intrinsic muscles of eyes and ciliary muscles for accommodation; damage results to external strabismus, dilated pupils (mydriasis) and loss of eye accommodation

Cranial Nerves Trochlear Nerve (CN IV)- arises at dorsal (posterior) surface of midbrain; Motor- innervates the superior oblique muscle; damage results to extortion of eye Abducens Nerve (CN VI)- arises at pons; Motor- innervates lateral rectus muscle; damage results to internal strabismus Trigeminal Nerve (CN V)- largest C.N.; Mixed, 3 branches - Opthalmic (sensory), Maxillary (sensory), Mandibular (sensory & motor); damage results to loss of sensation on the face, paralysis of muscles of mastication

Facial Nerve Facial Nerve (CN VII):- Arises at pons Mixed (motor and sensory) Motor: Somatic motor – muscles of facial expression, and Visceral motor - tear, nasal and palatine glands, and salivary glands Sensory: taste on anterior 2/3’s of tongue Damage: Bell’s palsy, dryness of eyes, dryness of mouth, loss of taste at anterior 2/3’s of tongue Vestibulocochlear Nerve (CN VIII)- arises at pons special sensory, a) vestibular branch for vestibular sense, and b) cochlear branch for audition Damage: vestibular dysfunction (loss of balance, nystagmus, tinnitus, dizziness, etc.), deafness

Vagus Nerve Glossopharyngeal Nerve (CN IX)- arises at medulla oblongata; Mixed – motor (swallowing, salivation); sensory (from posterior 1/3 of tongue, pharynx and palate, carotid arteries); damage results to dysphagia (paralysis of pharyngeal muscles), loss of taste from posterior 1/3 of tongue Vagus Nerve (CN X)- arises at medulla oblongata; Mixed, widely distributed in thorax and abdomen (swallowing, speech, regulation of viscera); damage results to dysphagia, speech problem, and dysfunction of viscera)

Accessory Nerve Spinal Accessory Nerve (CN XI)- arises at medulla oblongata; Motor - swallowing, head, neck and shoulder movement; damage results dysphagia, paralysis of sternocleidomastoid muscle and trapezius muscle Hypoglossal Nerve (CN XII)- arises at medulla oblongata; Motor - Tongue movements for speech, food manipulation; damage results to deviation of tongue to affected side (ipsilateral)

Cranial Reflexes Involve sensory and motor fibers of cranial nerves Clinically useful to check cranial nerve or brain damage Pupillary (light) reflex- sensory nerve (II C.N.), motor nerve (III C.N.) Corneal (blink) reflex- sensory nerve (V C.N.), motor nerve (VII C.N.)

Homework (Self Review) List the cranial nerves that are sensory, motor, and mixed nerves. Identify the cranial nerves involved in the following: tongue movement, smiling, balance and equilibrium, increase heart beat, contraction of sternocleidomastoid, parotid gland secretion, lacrimation (tearing), contraction of lateral rectus, smell of perfume, pinprick on the cheek, movement of eye upward, medial and downward, hoarseness of voice and vomiting, pupilloconstriction, vision, and hearing. Match the clinical condition as to cranial nerve injured. ___ anopsia a. VII C.N. ___ anosmia b. II C.N. ___ external strabismus c. XII C.N. ___ internal strabismus d. V C.N. ___ bell’s palsy e. VI C.N. ___ deviation of tongue to side of lesion f. I C.N. ___ pain and paralysis of muscles of mastication g. III C.N.