Cranial Nerve Examination

Cranial Nerves innervate ipsilaterally. I.e. they leave the brainstem on the same side of the face that they innervate. I.e. a left 7th nerve palsy will give a left sided facial weakness.

I Olfactory

Any problems with your sense of smell

II Optic

Inspect: remember pupillary reflexes: sensory=CNII Motor=CN III


Acuity (Snellen/ each eye individually)


Fundoscopy (separate video)


Internuclear Ophthalmoplegia is beyond the scope of this quick guide! But let it be said that the eye that doesn’t ADduct and the lesion is in the medial longitudinal fasciculus. Occurs almost exclusively in M.S.

III IV VI – Oculomotor, Trochlear, Abducens

General eye movements.

One hand on the patients head (permission) to steady it.

Change hands in the middle to do each side.

Stick to the “H” shape.

Remember nystagmus is complicated and can be from a number of different causes including cerebellar and peripheral causes

LR6 (SO4)3     Means… Lateral rectus is innervated by CN VI, The superior oblique (which actually makes the eye look down) is innervated by CN VI, and the rest are innervated by the 3rd nerve.

Remember the III (oculomotor) forms the motor part of the pupillary reflex, and also innervates the levator palpebrae: so in a complete 3rd nerve palsy you get:

  • Ptosis
  • Pupil that’s “down and out” like a boxer! (Unopposed CN III and CN VI)
  • A dilated pupil (unopposed CN3)

In a complete CN III palsy if you shine a light into that eye you will get a normal pupillary reflex on the other side, as the sensory component of the pupillary reflex is in CNII.

Clinical Gold

Medical Third Nerve vs. surgical third nerve

Medical 3rd nerve palsies often occur from infarction of the inner core of the nerve (vascular problem) the more distal pupillary fibres are spared.


In a surgical 3rd nerve the parasympathetic fibres that run from the Edinger Westphal nucleus very superficially over the 3rd nerve are prone to being compressed by external factors (i.e. tumour/ Posterior communicating artery aneurysm [remember this connects the Middle Cerebral Artery to Posterior Cerebral Artery]

i.e. in a “surgical “ 3rd nerve palsy you blow the pupil [unopposed sympathetic innervation via the sympathetic chain]

CN IV Trochlear


Can’t look downwards (lose your superior oblique innervation)

CN VI Abducens

Lose the lateral rectus and therefore can’t look outwards (this means you get a convergent squint)

CN V  Trigeminal

Sensory 3 facial regions – Ophthalmic, maxillary, mandibular.

  • Motor
  • Jaw jerk
  • Taste

Corneal reflex – in an exam it’s unlikely you’ll be asked to do this but you should be able to demonstrate it

AGAIN like the pupillary reflex this is a sensory component (CN V) and a motor component (CN VII)

CN VII Facial

– Motor and Sensory (taste and 2/3 tongue)

Remember: A Bells palsy is by definition

1) idiopathic ( so if it’s because of a car accident its not a Bells!)

2) a lower motor neurone problem

3) involves the whole of the Face ( including forehead)

A stroke (UMN CN VII palsy from a TACS) will spare the other forehead as the there is bilateral innervation.

CN VIII Vestibulocochlear

Controls balance and hearing

Weber’s (W – pointing to the middle of the head)

Rinne’s Test (Bone [mastoid process] vs. air)-

Clinically not used particularly by medical doctors but the understanding is important. Formal audiograms are their replacement…


In a case of conduction deafness (e.g. wax) if you slap a tuning fork in the middle of the forehead, the sound waves are transmitted through the bone. The ear deprived of stimuli through the conduction problem (e.g. wax) perceives the sound louder on the side with the conduction deficit. = conduction deafness

Clearly doing the same with a nerve (sensori-neural) problem the person will hear the sound loudest on the side with a functioning nerve.

CN IX, X    Glossopharyngeal & Vagus

Gag reflex

In the case of a unilateral nerve problem the uvula is pulled across to the other side.

CN XI Accessory

The accessory nerve ipsilaterally innervates trapezii (R&L trapezius).  But it also innervates the SCM (sternocleidomastoid)

Feel your neck: to turn in to the left, it’s actually the right sternocleidomastoid that is acting. Therefore if you can’t turn to the left, then it’s the right sided cranial nerve that’s at fault!

CN XII Hypoglossal

Tongue movements

Deviates towards the side of the lesion (i.e. The opposite of the gag reflex.

Fasciculation: think Motor Neurone disease as a differential.