Cranial nerves 1-6 Flashcards
What is CN I?
The olfactory nerve
Where does CN I originate?
It is paired anterior extension of the forebrain
What is the route of CN I?
Olfactory nerves in roof of nasal cavity –> through the cribriform foramen of the ethmoid bone –> forms the olfactory bulb –> travels to the olfactory tract to the temporal lobe olfactory cortex
What is the function of CN I?
It has a special sensory function for smell
What fibres carry CN I?
SVA (special visceral afferent) that carry smell from roof of nasal cavity to CNS
What does the nerve innervate?
epithelia lining the nasal cavity
How is it tested?
ask for difficulties or change in smell
What is the medical term for loss of smell?
anosmia
Why would anosmia occur?
- most commonly upper resp tract
- secondary to head trauma (shearing forces over the olfactory nerves)
- tumours at base of frontal lobe
What is CN II?
optic nerve
Where does CN II originate?
paired anterior extension of the forebrain
What is the route of CN II?
Retinal ganglion cells –> axons from optic nerve –> exits back of orbit via orbit canal –> fibres merge at optic chiasm –> occipital lobe visual cortex
What is the function of CN II?
special sensory - vision
What are the fibres involved with CN II?
special sensory afferent (SSA)
What occurs in the optic chiasm?
mixing of the sensory fibres from the right and left optic nerve
What does the optic tract contain?
sensory information from part of the right and left eye
How would you test for CN II?
-use opthalmoscope to look at the optic disc at the back of retina
What would show if there was raised incracranial pressure?
blurry and swollen )papilledema)
What would happen if a pituitary tumour was compression the optic chiasm?
bilateral hemianopia (bilateral visual symptoms)
What is the optic disc?
the point at which the nerve enters the retina
What is CN III?
the oculomotor nerve
Where does CN III originate?
mibrain
What is CNIII path?
midbrain –> lateral wall of cavernous sinus –> superior orbital fissure
What does CN III supply?
- mnost extra-ocular muscles that move the eyeball
- levatory palpebral superioris
- sphincter pupillae (constricts the pupil)
What is its function?
motor and autonomic parasympathetic (eye movement and eyelid movement)
What does the parasympathetic supply?
the sphincter pupillae
What fibres are associated with CN III?
GVE and GSE - General visceral efferent and general somatic efferent
Which fibres is associated with the parasympathetic?
GVE (general visceral efferent)
What is the function of the ciliary muscle?
constrols pupil constriction and lens thickness (sphincter pupillae too?
How would you test CN III?
- inspect eyelids and pupil size
- pupillary reflexes
What is the typical presentation of the oculomotor injury?
down and out eye (have to lift lid to see the eye due to weak muscle
What can happen with increased intracranial pressure?
the uncus of the brain herniates of the edge of the tentorium cerebelli and compresses the nerve
What is diplopia?
double vision
What can pathology cause?
diplopia and pupillary dilation
What are the causes for pathology of CN III?
- raised intracranial pressure
- tumour / haemorrhage
- cavernous sinus thrombosis
- secondary to diabetes/hypertension
What will you find if the occulomotor nerve is compressors?
pupils constantly dilated as the parasympathetic fibres sit outside of the nerve so compression of the nerve will affect these fibres first
What is CN IV?
Trochlear nerve
Where does it originate?
midbrain
What is its route?
mid brain (ventral part) –> cavernous sinus –> superior orbital fissue
What is its function?
motor
What does CN IV do?
innervates the superior oblique muscle of the eyeball (depress and laterally rotates the eyeball)
Why does CN IV have the longest nerve route?
comes off the ventral part of the midbrain so has a longer intracranial route
How would you test for CN IV?
testing eye movements
What fibres does CN IV carry?
GSE
What pathologies of CN IV can you get?
- diplopia (rare)
- congenital palsies
- Head injury causing acute injury or raised ICP
What is CN V?
trigeminal nerve
What are its branches?
Va - opthalamic
Vb - maxillary
Vc - mandibular
Where does CN V originate?
the pons
What is the route of Va?
pons –> cavernous sinus –> superior orbital fissure –> orbit
What is the route of Vb?
pons –> cavernous sinus –> foramen rotundum –> pterygopalatine fossa
What is the route of Vc?
pons –> foramen ovale –> infra temporal fissure
What is the function of CN V?
general sensory and motor
What does CNV do?
- sensory nerve suppling skin of face and some skull
- sensory to deeper structures
- motor to muscles of mastication
What deeper structures does CN V supply?
- paranasl sinuses
- nasal and oral cavity
- sensation to anterior tongue
What branch supplies the muscles of mastication?
Vc
What are the important branches of Va and what do they do?
supra orbital and supra trochlear
-sensory from the forehead
What are the important branches of Vb and what do they do?
infraorbital and superior alveolar nerves
-sensory from cheek and lower eye lid AND sensory room deep structures of the face upper teeth and gum
What are the important branches of Vc and what do they do?
- inferior alveolar nerve, inguinal nerve, auriculotemproal
- sensory from mental protuberance, lower lip and gym
- general sensory from anterior tongue
- general sensory from ear, temp and TMJ
What nerve is blocked by dentists/ maxfax?
Vb - superior alveolar nerves
What branch is most susceptible to injury i mandibular fractures?
Vc - inferior alveolar nerve
How would you test for CNV?
- sensation to face
- muscles of mastication
- corneal reflex
What pathology of CNV can you get?
- shingles (involves ophthalmic brach
- trigeminal neuralgia (Vb contributes to sudden attack of sharp facial pain
What branch is most susceptible to injury in orbital floor fracture?
Vb - infraorbital branch
What is CN VI?
abducens nerve
Where does it originate?
lower pons
What is CN VI route?
lower pons –> runs upwards to pass through cavernous sinus –> superior orbital fissure
What is the function of CNVI?
motor
What muscle does it supply?
lateral rectus causing abduction of the eyeball
How would you test CNVI?
ask the patient to look to the right - the eye that doesn’t move is the one thats damages
What would the patient present with and why?
diplopia as the eyes aren’t aligned
Why can CNVI be easily stretched in raised ICP?
it emerges anterior at the ponto-medullary junction
What other pathologies can you get with CNVI?
micro-vascular complication in diabetes or hypertension
What fibres do CN V carry?
GSA and SVE
What fibres does CNVI carry?
GSE
How could an infection around the orbit spread intracranially?
-in opthlamic veins drain structures of the obit and drain mostly via the facial vein with which they anastomose - they also communicate with the cavernous sinus and as the veins are valveless, venous blood can pass in either direction
ANSWER ON EXAMPLIFY ABOUT PATIENT HAVIN DIPLOPIA AND A LARGE BRAIN TUMOUR IN THE FRONTAL LOBE AND RAISED ICP - HOW CAN YOU EXPLAIN HIS SYMPTOMS?
- optic nerve is an extension of the forebrain so carries the layers of the meninges with it
- raised ICP increases pressure in the subarachnoid space
- the nerve becomes external compressed
- compression on the optic nerve leads to disruption int he optic nerve function
