Neuroscience (Cranial Nerve Examination)

Question 1

Recap:

State the pathway of CN 1-3

Answer 1

CN 1 - OLFACTORY NERVE
- nasal mucosa –> cribiform plate –> frontal lobe –> temporal lobe

CN 2 - OPTIC NERVE
- orbital apex –> optic nerve –> optic chiasma –> optic tract –> LGN –> optic radiation –> visual cortex

CN 3 - OCULOMOTOR NERVE
- midbrain (superior colliculus) –> cavernous sinus –> superior orbital fissure –> orbital apex

Question 2

Recap:
State the pathway of CN 4-6

Answer 2

CN 4 - TROCHLEAR NERVE
- midbrain (inferior colliculus) –> wraps around cerebral peduncles –> cavernous sinus –> superior orbital fissure –> orbital apex

CN 5 - TRIGEMINAL NERVE
(V1) superior orbital fissure –> cavernous sinus –> trigeminal ganglion –> midpons
(V2) pterygopalatine fossa –> foramen rotundum –> cavernous sinus –> trigeminal ganglion –> midpons
(V3) infratemporal fossa –> foramen ovale –> trigeminal ganglion –> midpons

CN 6 - ABDUCENS NERVE
- pons –> pontomedullary junction –> cavernous sinus –> superior orbital fissure

Question 3

Recall:
State the pathways of CN 7-9

Answer 3

CN 7 - FACIAL NERVE
- pons –> pontomedullary junction –> internal acoustic meatus –> stylomastoid foramen –> pierces parotid gland (without supplying)

CN 8 - VESTIBULOCOCHLEAR NERVE
- pons –> pontomedullary junction –> internal acoustic meatus –> inner ear

CN 9 - GLOSSOPHARYNGEAL NERVE
- medulla –> jugular foramen –> palate (travels between IJV and ICA)

Question 4

Recall:

State the pathways of CN 10-12

Answer 4

CN 10 - VAGUS NERVE
- medulla –> jugular foramen –> various trgets (travels in carotid sheath with CCA and IJV)

CN 11 - SPINAL ACCESSORY NERVE
- medulla –> jugular foramen –> SCM and trapezius

CN 12 - HYPOGLOSSAL NERVE
- medulla –> hypoglossal canal –> tongue (travels close to digastric muscles and ECA)

Question 5

State the cranial nerves that traverse the cavernous sinus

Answer 5

CN III, CN IV, CN V1, CN V2, CN VII

Question 6

Which CN is prone to injury when a carotid artery lesion occurs?

Answer 6

HYPOGLOSSAL NERVE (CN XII)

Question 7

With reference to CN I (Olfactory N), state
(1) Test used to test function
(2) Disruptions

Answer 7

CN I - OLFACTORY NERVE
- Test = patient smells object placed directly in front of nose
- Disruptions = frontal head injury (injury to cribiform plate), rhinitis, kallman syndrome, parkinson’s diseas

Question 8

With reference to CN II (Optic N), state
(1) Common locations of lesions and their effects on vision
(2) Test used to test function
(3) Left eye poor acuity = ?
(4) Left visual field on both eyes blind = ?

Answer 8

With reference to CN II (Optic N), state
(1) Common locations of lesions and their effects on vision
- acuity pathology = damage to structures anterior to chiasm (eye, optic nerve)
- visual field pathology = damage to structures posterior to chiasm (optic tract, LGN, optic radiation, visual cortex)
(2) Test used to test function = test one eye at a time using own visual field as comparison to patient’s
(3) Left eye poor acuity = lesion in left optic nerve
(4) Left visual field on both eyes blind = right optic radiation after hemidecussation of nasal hemiretina fibres

Question 9

Recall:
State the 3 reflexes in cranial nerves. State the afferent and efferent limbs.

Answer 9

(1) pupillary light reflex
- afferent limb = CN II (optic N)
- efferent limb = CN III (oculomotor N)

(2) corneal reflex
- afferent limb = CN V (trigeminal N)
- efferent limb = CN VII (facial N)

(3) gag reflex
- afferent limb = CN IX (glossopharyngeal N)
- efferent limb = CN X (vagus N)

Question 10

Recall:
Draw out the pathway for pupillary light reflex.

Answer 10

Question 11

Recall:
Draw out the pathway for accommodation/convergence.

Answer 11

Question 12

If patient presents with a totally plegic eye + numbness over the upper ⅔ of the face, lesion is at?

Answer 12

Numbness over upper 2/3 of face - CN V1, V2 lesion
Plegic eye - CN III, IV and VI lesion

Result = Cavernous sinus lesion

Question 13

Recall:
Draw out the pathway for Corneal reflex.

Answer 13

Question 14

Describe the difference between the resultant effects of a stroke vs bell’s palsy.

State some other examples of pathologies that can elicit the same result as stroke and bell’s palsy respectively.

Answer 14

STROKE - UMN lesion for CN VII
- result = contralateral lower quadrant weakness, upper quadrants still have some sensation
- recieves innervation from ipsilateral UMN
- other examples of UMN lesion = tumour, inflammation

BELL’S PALSY - LMN lesion for CN VII
- result = entire contralateral face weakness
- other examples of LMN lesion = mumps and shingles

Question 15

With reference to CN VIII - Vestibulocochlear N,
(1) Sensorineural hearing loss = pathology in ?
(2) Conductive hearing loss = pathology in ?

Answer 15

With reference to CN VIII - Vestibulocochlear N,
(1) Sensorineural hearing loss = problem in inner ear/ CN VIII/ brainstem (sound not conveyed)
(2) Conductive hearing loss = problem in external/middle ear (sound not amplified)

Question 16

RINNE AND WEBER’S TEST (normal)

(1) RINNE’S TEST (BONE AND AIR CONDUCTION)
- ____ conduction is louder than ____ conduction
- This is because ____ conduction takes advantage of the ____ system from ____ ear (s)
- Whereas for ____ conduction, it bypasses ____ and hence will be softer

(2) WEBER’S TEST
- When tuning fork is placed in the middle of the forehead, vibrations are transmitted ____ to both ears resulting in ____ volume in both ears

Answer 16

RINNE AND WEBER’S TEST (normal)

(1) RINNE’S TEST (BONE AND AIR CONDUCTION)
- AIR conduction is louder than BONE conduction
- This is because AIR conduction takes advantage of the AMPLIFICATION system from EXTERNAL AND MIDDLE ear (s)
- Whereas for BONE conduction, it bypasses AMPLIFICATION and hence will be softer

(2) WEBER’S TEST
- When tuning fork is placed in the middle of the forehead, vibrations are transmitted EQUALLY to both ears resulting in EQUAL volume in both ears

Question 17

RINNE AND WEBER’S TEST (SENSORINEURAL HEARING LOSS)
- pathology of =

(1) RINNE’S TEST (BONE AND AIR CONDUCTION)
- During air conduction, sound is ____ by the ____ ear (s) and then ____ at the point of ____ injury
- During bone conduction, sound ____ the ____ system and then ____ at the point of ____ injury
- This results in ____ conduction being louder than ____ conduction but ____ than normal

(2) WEBER’S TEST
- Although both ears receive ____ signal, signal is ____ on ____ side resulting in sound being ____ on normal side.

Answer 17

RINNE AND WEBER’S TEST (SENSORINEURAL HEARING LOSS)
- pathology of = inner ear / brainstem / CN VIII

(1) RINNE’S TEST (BONE AND AIR CONDUCTION)
- During air conduction, sound is AMPLIFIED by the EXTERNAL AND MIDDLE ear (s) and then REDUCED at the point of SENSORINEURAL injury
- During bone conduction, sound BYPASSES the AMPLIFICATION system and then REDUCED at the point of SENSORINEURAL injury
- This results in AIR conduction being louder than BONE conduction but SOFTER than normal

(2) WEBER’S TEST
- Although both ears receive EQUAL signal, signal is ATTENUATED on AFFECTED side resulting in sound being LOUDER on normal side.

Question 18

RINNE AND WEBER’S TEST (CONDUCTIVE HEARING LOSS)
- pathology of =

(1) RINNE’S TEST (BONE AND AIR CONDUCTION)
- ____ conduction will no longer be ____ and instead even die out in the ____ ear (s)
- ____ conduction ____ the ____ ear(s) and reaches the ____ ear, effectively ____ the lesion
- This results in ____ conduction being louder than ____ conduction

(2) WEBER’S TEST
- Both inner ears receive ____ signal but affected side has ____ background noise
- This results in ____ side being louder than ____ side

Answer 18

RINNE AND WEBER’S TEST (CONDUCTIVE HEARING LOSS)
- pathology of = external / middle ear

(1) RINNE’S TEST (BONE AND AIR CONDUCTION)
- AIR conduction will no longer be AMPLIFIED and instead even die out in the EXTERNAL/MIDDLE ear (s)
- BONE conduction BYPASSES the EXTERNAL / MIDDLE ear(s) and reaches the INNER ear, effectively BYPASSING the lesion
- This results in BONE conduction being louder than AIR conduction

(2) WEBER’S TEST
- Both inner ears receive EQUAL signal but affected side has LESS background noise
- This results in AFFECTED side being louder than NORMAL side

Question 19

State the levels at which palatal muscle palsy can occur.

State the resultant presentation.

Answer 19

PALATAL MUSCLE PALSY
- Occurs at = CN IX, X
- Presentation = Palatal muscles weak on one side –> uvula pulled to opposite side

Question 20

State the nerves involved in gag reflex. State the pathway.

Answer 20

CN IX and X
- CN IX - afferent - supplies general sensory to pharynx
- CN X - efferent - supplies pharyngeal muscles → contract

Question 21

State the test to test for function of CN XII. State the presentation for left CN XII palsy.

Answer 21

Tongue strength → push against ice cream stick

Result = When the right genioglossus muscle is weak, the left genioglossus muscle pushes the tongue towards the right side

Causes of bulbar palsy = lesions to medulla + lesions to carotid A (especially ICA)