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Anatomy: Cranial Nerve Review

Here's my (new) mnemonic for remembering the cranial nerves:
"On Old Olympic Towering Tops A Feisty Virgin Grows Vines And Hops"

Next week I will be presenting on the nerves and the basics for testing them. I am beginning from a place of total ignorance, so skip or bear with me as I develop my notes. Free free to contribute relevant information, even if you are on my shit list. =-]


I. OLFACTORY
--location: from olfactory bulb through cribriform plate of the ethmoid bone to superior nasal cavity
--function: this nerve is the main one for our sense of smell
--clinical: anosmia can be caused by frontal or occipital head injury
--testing: hard to test because there are lots of things besides damage to this nerve that can cause the loss of smell--(such as sinus infections, old age, dementia, CNS sarcoidosis, zicam?, and more.) TESTING: Have pt close eyes, after some time waft something good smelling (coffee, peppermint, camphor) under the pt's nose and ask them to let you know when they smell something.
--other: if pt smells amonia when it is not there, can't tell the difference between ammonia and tap water when they are consecutively under his nose, probably has 5th cranial nerve issue. The other V tests will be normal.

II. OPTIC
--location: from optic chiasm via optic foramen to retina
--function: main nerve for vision
--clinical: anopia
--TESTING: visual field(s) reveal which portion of the nerve is damaged. One eye sees, the other does not? Or half of each eye's field? Outside halves? Or both left halves. All possible.

III. OCULOMOTOR
--location: two branches from brainstem (ventral midbrain) via superior orbital fissure to eyes
--function: eyelids, eyeball & pupil movement. Controls the inferior oblique = one of two eye elevator muscles. Primary fx: elevation of adducted eye, secondary: outward rotation of abducted eye.
--clinical: ptosis--eyelids droop, stabismus=eyes not fix on same thing, diplopia--double vision. Symptoms can be caused by an assortment of lesions but also by migraine, diabetes (common), hypertension, arteritis, and collagen-vascular disease.
--parasympathetic: fibers go to the pupillary sphincter and ciliary muscle of the eye
--has proprioceptive function
--TESTING: When right inferior oblique is paretic, image separation is greatest when pt looks up with right eye adducted. The false image comes from the right eye, is tilted, and is above the true image.

IV. TROCHLEAR
--from midbrain, smallest nerve from posterior brainstem via superior orbital fissure, this is the ONLY cranial nerve coming off the dorsum of the brain stem. The nerves decussate before they emerge, so the left trochlear nerve supplies the right superior oblique and vice versa.
--innervates superior oblique eye muscle, primary function: depresses the abducted eye, secondary function: inward rotation of the abducted eye. The oblique muscle rises in the apex of the orbit and its tendon runs through the pulley (trochlear) and then posterolaterally to insert in the posterior part of the eye behind the equator.
-- clinical: diplopia and strabismus.
--has proprioceptive function
--TESTING: When right superior oblique is pareitc, pt's chin is down and head is tilted and turned wiht left ear to left shoulder (not reliable). Image separation is greatest when pt is looking down with R eye adducted. One image is above the other, the false image is lower, tilted, and coming from the right eye.

V. TRIGEMINAL
--location: from the pons,
--three branches, the opthalmic (forehead), maxillary (top jaw up to bottom eyelid) and mandibular (temple to anterior bottom jaw)
--function: controls chewing, face & mouth touch & pain. Mostly sensory except madibular branch.
--mandibular branch is numbed dental anesthesia, also is motor to the pterygoids, masseter, temporalis, mylohyoid and anteriaio belly of the digastric muscles.
--clinical: with this nerve impact the ability to chew food. Largest nerve, two roots on pons.
--TESTING: Check pain perception in each region of the face testable using pin pricks, right and left, test touch with gentle touch (not swipe, that stims pain receptors) of tissue or cotton. There's a difference between pain & touch receptors so do both. Knowing which can help you localize the lesion. Also check the corneal reflex by touching the cornea with a tip of rolled up tissue sneaking in from the side while pt looks up & laterally. Correct reflex action is bilateral blink. Don't touch eyelash, sclera or pupil. If motor function of 3rd branch is affected, open mouth will deviate toward paralyzed side. Have pt open and close mouth.

VI. ABDUCENS
--location: from the pons to superior orbital fissure
--function: lateral rectus muscle of the eye turns eye laterally, abducts eye. Mixed nerve, mainly motor.
--clinical: "Wandering eye", the most common extraocular paresis.
--TESTING: Look at head posture. With paresis of the left lateral rectus, the chin is turned towrad the left shoulder as the pt faces you. The eyes are thus out of the area of control of the left lateral rectus. False duplicate images disappear when left eye is covered.


VII. FACIAL
--location: from the pons via stylomastoid foramen to face, scalp, neck.
--function: controls most facial expressions, secretion of tears & saliva, taste. Mixed nerve with motor, sensory and autonomic divisions. Motor function: frontalis to platysma (facial expressions), stapedius muscle in middle ear, stylohyoid and posterior belly of digastic. All muscles will be affected if lesion.
--parasympathetic: fibers to nasal, lacrimal and submandibular glands--Does this nerve make me salivate suddenly before I vomit?) (has proprioceptive function) (S/Sx of damage: can't close eyes, no taste, no saliva) Can be damaged by viruses such as Shingles or bacterial infcections such as Lyme disease. Bell's Palsy can result. TESTING AFFERENT FX: test sense of taste on anterior 2/3 of tongue
--HOW TO TEST: Watch pt while resting, talking, smiling, blinking. Ask pt to wrinkle forehead quickly a few times. Do eyebrows move equally? Ask pt to wrinkle forehead while providing gentle resistance. Ask pt to close eyes gently, then tightly, and try to open them while pt resists. If pt can wrinkle forehead and close eyes, it is not a 7th nerve lesion. More tests: show teeth, whistle, open wide, grimace to test platysma.

VIII. VESTIBULOCOCHLEAR
--from the medulla oblongata/pons to the spiral organ is mainly sensory, two branches, the vestibulo and the cochlear,
--function: controls auditory and equillibrium sensation, hearing and balance.
--clinical: damage to vestibular branch can cause vertigo, ataxia, nystagmus. Damage to the cochlear branch casus tinitis or deafness. Vertigo can also be caused by ateriosclorsis in the elderly, and by tricyclic antidepressants, symptom of temporal lobe seizure or can be benign in fast growing youth. Deafeness may result from acoustic neuroma, presbyacusis, otosclerosis, Meniere's disease, chornic ear infx, industrial abuse, trauma or drugs.
--parasympathetic: fibers to the parotid gland
--TESTING: Cochlear branch: key features of nerve deafness are loss of perception of high pitched sounds, and loss of hearing of bone conducted sound. Whispered speech at 6 feet, plug far ear and say numbers, have pt repeat numbers, normal can repeat 9/10 at this distance. If deafness then tuning fork to mastoid. (Conduction deafness causes loss of low tone appreciation. Total hearing loss is always nerve.)
--TESTING: Vestibular branch: observe eye movements in repsonse to hot and cold water in external ear canal, "caloric testing". Cold water inhibits fx of semicircular canalds, warm enhances it. Assess eye deviation and nystagmus. Cold is stronger stimulus than hot.

IX. GLOSSOPHARYNGEAL
--location: from the medulla oblongata to the back of tongue, tonsil and pharnyx as well as to the middle ear, upper pharnyx and parotid. Mixed: mostly sensory and motor to the stylopharyngeus muscle.
--function: taste, senses carotid blood pressure. Very important in swallowing.
--clinical: Damage can cause difficulty swallowing, decreased saliva and senation in the throat, and decreased taste sense.
--proprioceptive function: you know if you have swallowed it)
--TESTING Sensory fx: Cannot test sense of taste on posterior tongue. Check for touch sensitivity on pharnyx touching gently with a stick. Motor fx can't be tested clinically.

X. VAGUS
--location: from the medulla oblongata via jugular foramen to viscera. Mixed nerve to the heart, lungs, palate, trachea, bronci, GI. Sensory to the external ear.
--function: Senses aortic blood pressure, slows heart rate, stimulates digestive organs, taste,
--parasympathetic: fibers innervate gut organs including lungs, heart, esophagus, stomach, pylorus, entire small intestine, ileocecal valve and proximal half of the colon, liver, gallbladder, pancreas, kidneys and upper portions of the ureters.
--parasympathetic: about 75% of all parasympathetic fibers are here
--has proprioceptive function
--clinical: Damage to this nerve can cause the heart rate to increase, paralyze the vocal cords, loss of gut sensation and difficulty swallowing. Bubbling speech because mucus/saliva/food won't go down, remain in pharnyx and overflow into larynx, coughing, throat clearing with poor results, no gag reflex. Dysphagia. Poor sleep.
--other: The colon and below in the GI tract is innervated by 2nd and 3rd sacral nerves, sometimes 1st and 4th.
--TESTING: Pt say "ah", is midline of palate deviated? Paretic side remains lower. Uvula is not important. Bilateral palatal paraylsis causes nasal regurgitation and a nasal voice, pt can't pronounce b and g, you can hear air coming from nose as he talks.

XI. ACCESSORY
--location: from the medulla oblongata (from both brain stem and spinal cord) A mixed nerve.
--function: controls trapezius & sternocleidomastoid, helps with swallowing.
--has proprioceptive function
--clinical: Damage causes paralysis of the neck. Lesions in region of foramen magnum, upper spinal cord, lower medulla, also muscular dystrophy, lots more.
--TESTING: have pt turn head as far as they can to side, then place your hand on outside and have them push against your resistance to check strength of sternomastoid muscle. To test trapexiua, look at pt's back, is trapezius symmetrical? Pinch top strands of trapezius on both sides and have pt shrug--same on both sides?

XII. HYPOGLOSSAL
--location: from the meduall oblongata is a mixed but mostly motor nerve to tongue
--function: swallowing and speech.
--has proprioceptive function
--clinical: Damage causes difficulty chewing, swallowing, tongue curls toward affected side. Amyotrophic lateral sclerosis.
--TESTING: open mouth without sticking out tongue: is it thick/flat, central/deviated. "wasted tongue will appear lower in mouth". Have pt stick out tongue. Can they get it past teeth? It is symmetrical? If it deviates it will be toward the paralyzed side. Test tongue strength on each side by having pt push tongue against inside of cheek against your finger.


SACRAL NERVES

1. (occasional parasympathetic signal)

2. (parasympathetic fibers to the descending colon, rectum, urinary bladder and lower portions of the ureters, also to the external genitalia {erections!})

3. (parasympathetic fibers)

4. (occasional parasympathetic signal)


Useful website for info and review:
http://www.gwc.maricopa.edu/class/bio201/cn/cranial.htm

Comments

( 2 comments — Leave a comment )
(Anonymous)
Oct. 9th, 2007 01:31 pm (UTC)
Cranial
You look to have a better mnemonic device than in my boring old physio class. Good luck.
liveonearth
Oct. 10th, 2007 02:17 am (UTC)
Re: Cranial
Thanks! =-]
( 2 comments — Leave a comment )

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