Lesson 3 Cranial Nerves.docx

Know name, number, location, and function (sensory, motor, both), branches, impairment Test 50-65 questions What causes of cranial injuries and what sx are seen - Cranial nerves part of the PNS except CN II which is located in the meninges - Cranial nerves serve the head and neck except...

Know name, number, location, and function (sensory, motor, both), branches, impairment Test 50-65 questions What causes of cranial injuries and what sx are seen - Cranial nerves part of the PNS except CN II which is located in the meninges - Cranial nerves serve the head and neck except CN X (vagus) - Named from superior to inferior according to brain attachments or originations - Attachments - CN I -- Cerebrum - CN II -- Optic Chiasm (Hypothalamus) - CN III-IV -- Mesencephalon - CN V-VIII -- Pons - CN IX-XII -- Medulla - Parasympathetic fibers = CN 3, 7, 9, 10 - Cranial nerve injury causes = head trauma, infections, strokes, tumors, diabetes, high blood pressure, autoimmune disease - Olfactory Nerve (CN I) injury: Loss of smell - Olfactory nerve directly connects to cortex and bypasses thalamus - Olfactory cells continuously regenerate - Anosmia = loss of sense of smell - Anesthetic causes of anosmia = intranasal ketamine, intranasal 4% lido - Hyponosmia = decreased sense in smell - Ageusia = loss of taste functions of tongue - Anesthetic causes of ageusia = LMA over inflation, long use of LMA - Hypogeusia = reduction in one of the taste sensations (sweet, sour, bitter, salty, umami) - Dysgeusia = altered taste perception - Optic Nerve (CN II) injury: Vision loss or changes. - Optic chiasm located at base of brain and where the optic nerve crosses - Optic nerve located 10 mm superior to pituitary gland and anterior floor of 3^rd^ ventricle and circle of Willis very vulnerable to compression - Corneal abrasion is most common postop ocular injury - Most common causes of permanent POVL = CRAO, ION, cerebral vision loss - POVL related to cardiac surgery, spine surgeries - Ischemic optic neuropathy - Painless vision loss in the immediate postop period - Risk factors = diabetic, smoker, HTN, intraoperative hypotension, prolonged surgeries, prone position - Prevention = minimize pt movement, manage BP intraop - CN II nerve blocks - Types of blocks = retrobulbar bloc, sub tenon technique, peribulbar anesthesia - Complications = unintentional injection resulting in partial or total brainstem anesthesia - Oculomotor Nerve (CN III) injury: Double vision, drooping eyelid, pupil dilation. - CN III controls eye movement, eyelid movement, pupil constriction & contractions of most eye muscles - Sx of injury = down & out position of the eye, ptosis, mydriasis (topical local anesthetic and regional block) - Trochlear Nerve (CN IV) injury: Difficulty moving the eye downward or inward. - CN IV is smallest cranial nerve with the longest intracranial course - Sx of injury = head tilt away from affected side, vertical diplopia worsened by looking down and inward - Trigeminal Nerve (CN V) injury: Facial pain, loss of sensation, difficulty chewing. - Opthalmic branch of CN V - Sensory → superior aspect of the face, eyeball, lacrimal gland, conjunctiva, nasal mucosa - Mediates afferent portion of oculocardiac reflex (5 and dime reflex) - Oculocardiac reflex triggers = traction of extraocular muscle or direct pressure on the glob - Manifestations = decreased HR, junctional ehythm, ectopic beats, AV block, v tach, asystole - Prevention and treatment = stop pressure/traction, deepen anesthetic, anticholinergics for HR - Vagus (CN X) nerve mediates efferent portion of oculocardiac reflex - Maxillary branch of CN V - Sensory to bottom of nose, maxilla, maxillary teeth/gums. - Mandibular branch of CN V - Carries motor (efferent) nerves - Sensory to skin of mandable, and mandibular teeth/gums - Trigeminal neuralgia (tic doloroux) - Uncertain cause →can occur d/t nerve compression from blood vessel. - Treated w/ Tegretol (carbamazepine) or surgical decompression - Abducens Nerve (CN VI) injury: Inability to move the eye outward/laterally/abduction - Symptoms = diplopia, strabismus (lazy eye), head rotation to allow for sideways vision - Facial Nerve (CN VII) injury: Facial weakness or paralysis, drooping of the mouth or eyelid, loss of taste on the front two-thirds of the tongue - 5 branches = Two Zebras But My Cookie = Temporal, Zygomatic, Buccal, Marginal Mandibular, Cervical - Facial nerve monitoring is placed at the orbicularis oculi muscle to measure onset of NMB - Orbicularis oculi muscle recovers faster than upper airway function so recovery is best measured in ulnar nerve - Bell's palsy = idiopathic facial palsy - Vestibulocochlear Nerve (CN VIII) injury: Hearing loss, balance issues. - 2 branches (vestibular and cochlear fibers) combine in the pons to form the vestibulococlear nerve - Injury can occur from basilar skull fracture - Vestibular neuritis can result from HSV - Vestibular neuritis treatment = anti-emetics, vestibular suppressants (e.g. meclizine) - Labrinthisitis is inflammation of both branches - Ototoxic drugs - Glossopharyngeal Nerve (CN IX) injury: Difficulty swallowing, loss of taste on the back third of the tongue. - Tympanic- carries parasympathetic fibers- Jacobson - Tonsillar- provides sensory innervation to the palatine tonsils - Stylopharyngeal- provides motor innervation to the stylopharyngeus muscle - Carotid sinus nerve- communicates with the Vagus nerve to carry signals to the baroreceptors (carotid sinus) and chemoreceptors( carotid body) - Hering's nerve = carotid sinus nerve - Hering's nerve innervates the carotid sinus and carotid body -- regulates BP and monitors O2 and CO2 levels in brain - Pharyngeal- joins with the pharyngeal of CN X & sympathetic nerves to form the pharyngeal plexus- innervate the muscles of the pharynx - Lingual branches- supply the vallate papillae, mucous membranes, and follicular glands of the posterior tongue - CN IX dysfunction = Posterior cranial fossa tumor, Styloid fracture, Eagle syndrome, Iatrogenic injury with LMA - CN IX injury sx = dysphagia, loss of carotid sinus reflex, loss of gag reflex - Vagus Nerve (CN X) injury: Voice changes, difficulty swallowing, irregular heart rate. - Vagus nerve provides sensory information from internal organs to solitary nucleus - Parasympathetic motor functions = slow phase 4 depolarization of heart, muscarinic increase in bronchial constriction, stimulates peristalsis and secretion of digestive enzymes - Vagus innervates SLN and RLN -- larynx innervation - RLN provides motor function to all muscles of the larynx except cricothyroid muscle - Hering-Breuer reflex mediated by vagus nerve - Vagus transmits stretch sensations from bronchi to brainstem respiratory groups - Pulmonary stretch receptors - activated d/t excess stretch of bronchi/alveoli - Stretch & afferent signal causes respiratory centers to shut off the inspiratory impulse in neonates/infants - This afferent pathway is the same as the one involved in sinus arrythmia in adults - Pediatric patients are more susceptible to vagal stimulation than adults - Causes of perioperative increased vagal tone = stimulation, hypoxia, manipulation of carotid bodies, peritoneal insufflation, anticholinesterase inhibitors - Spinal Accessory Nerve (CN XI) injury: Weakness in shoulder and neck muscles. - CN XI innervates sternocleidomastoid and trapezius - Spinal and cranial parts of CN XI - Cranial part is considered to be part of the vagus nerve - Accessory nerve palsy is usually iatrogenic - Hypoglossal Nerve (CN XII) injury: Difficulty speaking, swallowing, and moving the tongue - 4 branches = meningeal, descending, thyrohyoid, muscular/lingual branch - Muscular lingual branch is the one that controls most actions of the tongue - Muscular lingual branch only one considered to be part of real hypoglossal nerve originating from hypoglossal nucleus - Can be injured during carotid endarterectomy - Innervates all tongue muscles except the palatoglossus - When damaged, tongue will deviate towards to damaged nerve - In supranuclear hypoglossal nerve lesions cause tongue to protrude away from nerve because of neural crossing for upper motor neurons -