Cranial nerves 1-6

Question 1

What is CN I?

Answer 1

The olfactory nerve

Question 2

Where does CN I originate?

Answer 2

It is paired anterior extension of the forebrain

Question 3

What is the route of CN I?

Answer 3

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

Question 4

What is the function of CN I?

Answer 4

It has a special sensory function for smell

Question 5

What fibres carry CN I?

Answer 5

SVA (special visceral afferent) that carry smell from roof of nasal cavity to CNS

Question 6

What does the nerve innervate?

Answer 6

epithelia lining the nasal cavity

Question 7

How is it tested?

Answer 7

ask for difficulties or change in smell

Question 8

What is the medical term for loss of smell?

Answer 8

anosmia

Question 9

Why would anosmia occur?

Answer 9

• most commonly upper resp tract
• secondary to head trauma (shearing forces over the olfactory nerves)
• tumours at base of frontal lobe

Question 10

What is CN II?

Answer 10

optic nerve

Question 11

Where does CN II originate?

Answer 11

paired anterior extension of the forebrain

Question 12

What is the route of CN II?

Answer 12

Retinal ganglion cells –> axons from optic nerve –> exits back of orbit via orbit canal –> fibres merge at optic chiasm –> occipital lobe visual cortex

Question 13

What is the function of CN II?

Answer 13

special sensory - vision

Question 14

What are the fibres involved with CN II?

Answer 14

special sensory afferent (SSA)

Question 15

What occurs in the optic chiasm?

Answer 15

mixing of the sensory fibres from the right and left optic nerve

Question 16

What does the optic tract contain?

Answer 16

sensory information from part of the right and left eye

Question 17

How would you test for CN II?

Answer 17

-use opthalmoscope to look at the optic disc at the back of retina

Question 18

What would show if there was raised incracranial pressure?

Answer 18

blurry and swollen )papilledema)

Question 19

What would happen if a pituitary tumour was compression the optic chiasm?

Answer 19

bilateral hemianopia (bilateral visual symptoms)

Question 20

What is the optic disc?

Answer 20

the point at which the nerve enters the retina

Question 21

What is CN III?

Answer 21

the oculomotor nerve

Question 22

Where does CN III originate?

Answer 22

mibrain

Question 23

What is CNIII path?

Answer 23

midbrain –> lateral wall of cavernous sinus –> superior orbital fissure

Question 24

What does CN III supply?

Answer 24

• mnost extra-ocular muscles that move the eyeball
• levatory palpebral superioris
• sphincter pupillae (constricts the pupil)

Question 25

What is its function?

Answer 25

motor and autonomic parasympathetic (eye movement and eyelid movement)

Question 26

What does the parasympathetic supply?

Answer 26

the sphincter pupillae

Question 27

What fibres are associated with CN III?

Answer 27

GVE and GSE - General visceral efferent and general somatic efferent

Question 28

Which fibres is associated with the parasympathetic?

Answer 28

GVE (general visceral efferent)

Question 29

What is the function of the ciliary muscle?

Answer 29

constrols pupil constriction and lens thickness (sphincter pupillae too?

Question 30

How would you test CN III?

Answer 30

- inspect eyelids and pupil size | - pupillary reflexes

Question 31

What is the typical presentation of the oculomotor injury?

Answer 31

down and out eye (have to lift lid to see the eye due to weak muscle

Question 32

What can happen with increased intracranial pressure?

Answer 32

the uncus of the brain herniates of the edge of the tentorium cerebelli and compresses the nerve

Question 33

What is diplopia?

Answer 33

double vision

Question 34

What can pathology cause?

Answer 34

diplopia and pupillary dilation

Question 35

What are the causes for pathology of CN III?

Answer 35

- raised intracranial pressure - tumour / haemorrhage - cavernous sinus thrombosis - secondary to diabetes/hypertension

Question 36

What will you find if the occulomotor nerve is compressors?

Answer 36

pupils constantly dilated as the parasympathetic fibres sit outside of the nerve so compression of the nerve will affect these fibres first

Question 37

What is CN IV?

Answer 37

Trochlear nerve

Question 38

Where does it originate?

Answer 38

midbrain

Question 39

What is its route?

Answer 39

mid brain (ventral part) --> cavernous sinus --> superior orbital fissue

Question 40

What is its function?

Answer 40

motor

Question 41

What does CN IV do?

Answer 41

innervates the superior oblique muscle of the eyeball (depress and laterally rotates the eyeball)

Question 42

Why does CN IV have the longest nerve route?

Answer 42

comes off the ventral part of the midbrain so has a longer intracranial route

Question 43

How would you test for CN IV?

Answer 43

testing eye movements

Question 44

What fibres does CN IV carry?

Answer 44

GSE

Question 45

What pathologies of CN IV can you get?

Answer 45

- diplopia (rare) - congenital palsies - Head injury causing acute injury or raised ICP

Question 46

What is CN V?

Answer 46

trigeminal nerve

Question 47

What are its branches?

Answer 47

Va - opthalamic Vb - maxillary Vc - mandibular

Question 48

Where does CN V originate?

Answer 48

the pons

Question 49

What is the route of Va?

Answer 49

pons --> cavernous sinus --> superior orbital fissure --> orbit

Question 50

What is the route of Vb?

Answer 50

pons --> cavernous sinus --> foramen rotundum --> pterygopalatine fossa

Question 51

What is the route of Vc?

Answer 51

pons --> foramen ovale --> infra temporal fissure

Question 52

What is the function of CN V?

Answer 52

general sensory and motor

Question 53

What does CNV do?

Answer 53

- sensory nerve suppling skin of face and some skull - sensory to deeper structures - motor to muscles of mastication

Question 54

What deeper structures does CN V supply?

Answer 54

- paranasl sinuses - nasal and oral cavity - sensation to anterior tongue

Question 55

What branch supplies the muscles of mastication?

Answer 55

Vc

Question 56

What are the important branches of Va and what do they do?

Answer 56

supra orbital and supra trochlear | -sensory from the forehead

Question 57

What are the important branches of Vb and what do they do?

Answer 57

infraorbital and superior alveolar nerves | -sensory from cheek and lower eye lid AND sensory room deep structures of the face upper teeth and gum

Question 58

What are the important branches of Vc and what do they do?

Answer 58

- 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

Question 59

What nerve is blocked by dentists/ maxfax?

Answer 59

Vb - superior alveolar nerves

Question 60

What branch is most susceptible to injury i mandibular fractures?

Answer 60

Vc - inferior alveolar nerve

Question 61

How would you test for CNV?

Answer 61

- sensation to face - muscles of mastication - corneal reflex

Question 62

What pathology of CNV can you get?

Answer 62

- shingles (involves ophthalmic brach | - trigeminal neuralgia (Vb contributes to sudden attack of sharp facial pain

Question 63

What branch is most susceptible to injury in orbital floor fracture?

Answer 63

Vb - infraorbital branch

Question 64

What is CN VI?

Answer 64

abducens nerve

Question 65

Where does it originate?

Answer 65

lower pons

Question 66

What is CN VI route?

Answer 66

lower pons --> runs upwards to pass through cavernous sinus --> superior orbital fissure

Question 67

What is the function of CNVI?

Answer 67

motor

Question 68

What muscle does it supply?

Answer 68

lateral rectus causing abduction of the eyeball

Question 69

How would you test CNVI?

Answer 69

ask the patient to look to the right - the eye that doesn't move is the one thats damages

Question 70

What would the patient present with and why?

Answer 70

diplopia as the eyes aren't aligned

Question 71

Why can CNVI be easily stretched in raised ICP?

Answer 71

it emerges anterior at the ponto-medullary junction

Question 72

What other pathologies can you get with CNVI?

Answer 72

micro-vascular complication in diabetes or hypertension

Question 73

What fibres do CN V carry?

Answer 73

GSA and SVE

Question 74

What fibres does CNVI carry?

Answer 74

GSE

Question 75

How could an infection around the orbit spread intracranially?

Answer 75

-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

Question 76

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?

Answer 76

- 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