Cranial Nerves Flashcards
CN I
- Olfactory Nerve
- arise from olfactory epithelium (upper 1/3 of nasal cavity)
- pass through cribriform plate (ethmoid bone), terminate in primary olfactory cortex
CN I tests
Olfactory N
•test patency of nostril
•have them smell something like coffee, lemon extract, alcohol swab
•Anosmia-multiple causes including TBI
Nerves involved in vision
CNs II, III, IV, VI
CN II
- Optic nerve
- pass through optic canals (sphenoid bone), travel in optic tracts and converge at optic chiasm
- continue and synapse at thalamus; from there, optic radiation fibers run to visual cortex
CN III
- occular motor nerve
- extend from ventral midbrain
- sperior orbital fissure (spenoid bone)
- somatic motor to eyelid and 4 external ocular muscles (Middle rectus (look medial), superior rectus (look up and out), inferor recuts (look down and out), inferior oblique (look up and in))
- PSNS motor to sphincter muscles of iris–>dialate–>from ciliary ganglion
- lesion would cause pt to be unable to open eyelid, eye would face down and out as SR, LR are unopposed
CN IV
- Trochlear n
- emerge from dorsal midbrain (only CN on dorsal side of midbrain)
- superior orbital fissures (sphenoid bone)
- innervate superior oblique muscle (down and in)
- longest and thinest of the cranial nerves (easily compressed)
- impairment leads to eye resting looking up)
CN VI
- Abducens
- leave from inferior pons; superior orbital fissure (spenoid bone)
- innervate lateral rectus muscle (abducts the eye)
- impairment–>eye appears normal when looking forward, but pt is unable to move eye to the imparied side
Eye exam sequence
(1. History)
2. Inspection
3. Visual Acuity (eye chart)
4. fisual fields (confrontation)
5. ocular alignment
6. pupillary examination
7. opthalmoscopy
Visual field defects
- one eye blindness-leison to optic nerve
- bitemporal anop(s)ia-often caused by pituitary tumor (which sits just superior to optic chiasm)–>loose vision on lateral/temporal sides of both eyes
- hemianop(s)ia–>lesion in optic tract–>loose vision on the same side of both eyes
Extra-occular motor exam
•have pateint follow something to make a figure 8 shape–>if they get diplopia (double vision) with a certain movement is a positive test
Pupillary reflexes
- Afferent limb: CNII; Efferent limb: CN III, PS componenet
- light reflex: shine light in eye–>ipislateral iris constricts (direct light reflex), and contralateral iris constricts (consensual reflex)
- accomodation reflx (for near objects)–>attempt to focus on close object, pupil constrics (pupillary constrictor muscle), lends “rounds up” (ciliary muscles) for increase refraction
CN V
Trigeminal N •originates from ventral pons •V1: Ophthalmic S •V2: Maxillary S •V3: Mandibular S & M •trigeminal ganglion (sensory) in a dural cave (Meckle's) •passes through cavernous sinus
V1
- Opthalmic n
- superior orbital fissure (sphenoid)–>orbit–>superior orbital notch (frontal bone)
- Sensory to eye, forehead, nasal cavity
V2
- Maxillary n
- foramen rotundum (shpenoid)–>maxillary sinus (in body of maxilla)–>infraorbital foramen (maxilla)
- sensory to cheek, upper lip, teeth adn nasal avity
V3
- Mandibular n
- forament ovale (sphenoid bone)–>mandibular foramen (mandible)–>mental foramen (mandible)
- motor to muscles of MASTication (masseter, temporalis, pterygoids)
- motor to MATT muscles (mylohyoid, ant. digastric, tensor tympani, tensor veli palatini)
- sensory to lower lip, teeth, chin & tounge (touch)
CN VII
- Facial Nerve
- Exit cranial cavity w/ CN VIII through internal auditory meatus; exit skull through stylomastoid foramen (both temporal bone)
- 5 somatic efferent brances for muscles of facial expression (temporal, zygomatic, buccal, mandibular, cervial)
- chorda tympani–>through stylomastoid foramen: taste to ant 2/3 of tounge (special sense); PSNS to submandibular, sublingual salivary, and lacrimal glands
Testing CN V
- Inspection
- Palpation of masseter/temporalis
- test sensation V1, V2, V3
- corneal reflex (touch cornea) (afferent is V1)
- Jaw jerk (both branches should be V3)
Testing CN VII
- observe facial syymmetry
- forehead wrinkling, eyelid closure, whistle/pucker
- blink/corneal reflex (VII motor)
Tic douloureux
- trigeminal neuralgia
- most excruciating pain known (suicide disease)
- inflammation of nerve
- in severe cases, never ablated–>lead to loss of function of muscles of mastication and others
Bell’s Palsy
- Palsy of CN VII
- paralysis of facial muscles on affected side, loss of taste sensation
- caused by HSV-I infection of soma of CN VII neurons
- lower eyelid droops and eye cannot be closed (dry eye)
- condition may disappear spontaneously without treatment, some people respond to steroid treatment
- temporary or permanent
CN VIII
- Vestibulocochlear nerve
- 2 division: cochlear (hearing) and vestibular (balance) (only special sense)
- pass trough internal auditory meatus (temporal bone)
- enter brainstem at pons-medulla border
Testing CN VIII
•Cochlear
- acuity: whisper test, finger rub, hx
- rinne (the one on the side), weber (the one on the forehead)
•Vestibular-balance idk, didn’t say
CN IX
•Glossopharyngeal n
•emerge from lateral medulla
•exit via jugular foramen (temporal and occipital bones)
-motor: to stylopharyngeus & PSNS to parotid
-sensory: taste and general sesory from tounge and pharynx
-Parasympathetic: to parotid
-Visceral afferent: from carotid body
CN X
•Vagus n
•emerge from lateral medulla
•exit via jugular foramen (temporal and occipital bones) within carotid sheath
-general sensation from larynx and part of laryngopharynx and a small part of ext auditory meatus (temporal bone)
-visceral afferents from esophagus, foregut, midgut, bronchi, lungs, heart, and carotid body
-parasympathetic for smooth muscles and glads of larynx, parynx, airway, foregut adn midgut
-motor for pharynx (except stylopharyngeus), larynx, platoglossus, and muscles of soft palate (except tensor veli palatini)
-taste from epiglottis
