CRANIAL NERVE EXAMINATION

INTRODUCTION

Cranial nerves are a set of nerves that emerge directly from the brain. There are 12 pairs of cranial nerves, each has a unique function

Their functions are sensory, motor or both

• Sensory cranial nerves help a person to see, hear, smell or feel touch
• Motor cranial nerves help control muscle movements of eyes, head and neck
• Cranial nerves with both functions are also called mixed nerves
• Some cranial nerves also function as parasympathetic nerve(craniosacral outflow)

In this article, we will talk about their functions, examination and an easy way to remember these.

Before we jump on to the examination, let’s talk about some terminologies and short forms that we are going to use here

General – serve general motor, sensory functions like spinal nerves

Special- use special receptors & neurons to serve specialized functions

Somatic – innervate somatic muscles(muscles that arise from the soma, voluntary muscle contraction)

Visceral – innervate viscera(internal body) structures

GSA – general somatic afferent, mediates information from muscles, skin, ligament and joints

GSE – general somatic efferent, activates muscles from somites(skeletal,extraocular)

GVA- general visceral afferent, mediates sensory innervation from visceral organs

GVE – general visceral efferent, activates visceral organs

SVE – special visceral efferent, activates muscles of face, palate, mouth, pharynx and larynx excluding eye and tongue muscles

SVA – special visceral afferent, mediates visceral sensation of taste from tongue, olfaction from nose.

SSA – special somatic afferent, mediates special sensations of vision from retina & audition, equilibrium from inner ear

Nuclei – it refers to the structures that contains a number of cell bodies of the central nervous system, forms the gray matter of the brain

EXAMINATION

1. Olfactory nerve(SVA)

Procedure – take a piece of fruit, rose water, coffee or camphor & ask the patient to identify these smells. Each nostril is tested separately

Findings

• if the patient is able to identify properly – normal
• The patient is unable to recognise scents but recognises ammonia – Anosmia
• The abnormality is limited to one nostril- unilateral anosmia
• The patient doesn’t recognise any smell including ammonia – consider the loss to be organic

* remember not to use irritants like alcohol *

2. Optic nerve(SSA)

Examination includes visual acuity testing, perimetry, pupillary examination

1. Visual acuity testing through snellen chart(with the patient 6m away), Color vision testing through ishihara test

• Look at patient’s eyes and look for any asymmetry like ptosis or lid retraction(eyelid is higher than normal)

2. Visual field testing through confrontation test, amsler grid, tangent screen scotometry

• Confrontation test- examiner sits in front of the patient at a distance of 60 cm
• Patient is asked to cover one eye & stare at the examiner, the examiner will also close one eye, for ex if patient closes his left eye, then examiner will close his right eye
• The examiner will wiggle/move his finger, the patient has to identify which finger is moving and in which direction without breaking the stare
• All the four quadrants are tested

Pupil examination

• Size, outline
• Pupillary light reflex – look at reaction of the same eye which is tested(direct pupillary light reflex), look at reaction of the opposite eye (consensual light reflex)
• The direct light reflex is controlled by optic nerve, consensual light reflex is controlled by oculomotor nerve

3. Oculomotor nerve(GSE), trochlear(GSE), abducent(GSE)

Check for PERRLA(pupils equal,round,reactive to light and accommodation)

Saccadic eye movements- rapid movement from one point of fixation to another e.g movement to look from the page of a book to lamp or TV

Pursuits- slow eye movements used to maintain fixation on a moving object e.g to maintain eye contact

Vestibulo- ocular reflex- it is a gaze stabilising reflex, acting to stabilise gaze during head movement

Test ocular movement by making H with your finger or pen and ask patient to trace that H with his eyes

Test for convergence – the movement that maintain fixation as object is brought close to your face

Test for squint by cover test – ask patient to look with both eyes at a pen or in examiner’s right eye, then cover his left eye, uncover the left eye rapidly and cover right eye. Look to see if the left eye has corrected to look back at examiner’s eye

Test for ptosis with one eye deviated down and out or diplopia

Look for eyes aligned in different vertical planes(skew deviation)

Tip – SO4 LR6(superior oblique by trochlear nerve(CN4), lateral rectus by abducent(CN6))

4. Trigeminal nerve(SVE)(V1,V2,V3)

Sensory to the face V1- ophthalmic, V2- maxillary, V3- mandibular

Motor – muscles of mastication

Examination – touch with cotton swab for examination of light touch, sharp end of a pin for pain and test tubes with hot and cold water for temperature(40–45 degree c for hot, 4.44 degree c for cold, temperature between 5–10 degree c can also be used), tuning fork of 30 cps can be used for vibration

For motor examination- ask the patient to clench his or her teeth, look for wasting of muscles and check muscle strength according to MMT(functional, weak functional, nonfunctional, zero)

Test for jaw jerk – there should be slight closure of the jaw

Test for corneal reflex- ask the patient to look up and away from you. Approach from other side of patient’s line of vision. Touch the cornea lightly with a wisp of cotton. Look for blinking response of the eye.

5. Facial nerve(GSA)

Motor – muscles of the face, test by asking the patient to make different facial expressions like smiling, pouting, raising eyebrows, etc

Sensory – check for taste sensation in anterior 2/3rd of tongue by using salt or sugar. Ask the patient to close his eyes and identify the taste

Check for nasolabial folds and forehead wrinkles on both sides of the face and tear secretion from the eyes

*In Bell’s palsy, also known as infranuclear palsy or LMN palsy, whole half of a face is affected along with forehead and ipsilateral side of face is affected while in supranuclear or UMN palsy forehead is spared and contralateral side of face is involved, it commonly occurs along with stroke*

Check for bell’s phenomena- eyes turning upwards on attempted closure

6. Vestibulocochlear nerve(SSA)

Function – hearing and balance

To test hearing, most commonly 2 types of tests are used rinne’s test and Weber’s test by using a tuning fork of 512 hz

Rinne’s test – it’s performed by placing a vibrating tuning fork against the patient’s mastoid process to test bone conduction and asking the patient to indicate when the sound can no longer be heard. Once indicated, quickly position the still vibrating tuning fork 1–2 cm from auditory canal to test air conduction and ask the patient if they are able to hear it

Result –

• air conduction > bone conduction
• if bone conduction > air conduction, it is indicative of conductive hearing loss
• If both types of conduction are equally diminished, it’s indicative of sensorineural hearing loss

Weber’s test – in this, a vibrating tuning fork is placed in the middle of the forehead, above the upper lip or over glabella, patient is asked to report in which ear the sound is louder

Result –

• Sound should be heard equally in both ears
• In an affected patient, if the abnormal ear hears it louder, it indicates conductive hearing loss
• If the normal ear hears it louder, it indicates sensorineural hearing loss in the opposite ear

*these tests are for screening, they are not replacements for audio entry hearing tests*

Balance/vestibular assessment

Gait- heel – toe walking, unsteady, deviation to the side of walking is common

Nystagmus- latency of onset – 5- 10 seconds, rotational nystagmus is present, if there’s upbeating or downbeating a CNS dysfunction might be present

Romberg’s test- patient is asked to stand with feet together with eyes first open and then closed, the patient sways to the side of the lesion in peripheral vestibular lesions. In central lesions, patient shows general instability.

Dix- hallpike test

If rotational nystagmus occurs, test is positive and may indicate BPPV. If the test is negative, CNS dysfunction can be considered.

7. Glossopharyngeal nerve(SVE)

Motor – stylopharyngeus

Sensory – posterior 1/3rd of tongue, pharynx, middle ear

Test for gag reflex – touch pharyngeal wall with a stick and watch uvula, it should lift following the stimulus

You can also ask the patient to make AHH sound with mouth open and observe uvula

Findings-

• uvula moves to one side indicates motor neuron lesion,
• if the uvula doesn’t move on saying AHH or gag suggest bilateral muscle paralysis
• Uvula moves on saying AHH but not on gag suggests glossopharyngeal palsy

Examination of larynx

• Ask patient to cough or examiner can initiate coughing by reflexive cough
• Procedure for reflexive cough – ask the patient to take a deep breath, as the client holds breath, using palm of hand, push downward(toward stomach) on the sternum. Strength of cough is evaluated
• Observe for ease and loudness of cough
• If the cough is of a gradual onset it indicates vocal cord palsy

Observe for swallowing and speech

Check for taste sensation in posterior 1/3rd of tongue same as facial nerve

8. Vagus nerve(GVA)

Sensory – tympanic membrane

Motor – muscles of palate

Examination – tested in the same way as glossopharyngeal nerve

9. Spinal accessory nerve(SVE)

Function- motor innervation to trapezius and sternocleidomastoid(SCM)

Examination – perform manual muscle testing(SCM)

• Ask the patient to turn his head to one side and lift his head against resistance. Observe for both sides

Trapezius

• Ask the patient to shrug shoulders with and without resistance

Findings

• Weakness of ipsilateral SCM and contralateral trapezius indicates upper motor neuron lesion
• Bilateral wasting and weakness of SCM indicates myopathy

10. Hypoglossal nerve(GSE)

Motor- intrinsic muscles of tongue

Examination

Observe tongue for fasciculations, size, color

Ask the patient to push his tongue into the cheek and protrude, lateralise, elevate the tongue. Observe for deviation of the tongue. Fasciculations suggest LMN lesion

Test speech and ask the patient to say tick, tock as fast as he can.

How to remember?

Mnemonics make everything easy. Here’s one

How is it relevant to an OTist?

Therapists who work in clinical settings or hospitals must be equipped to deal with any challenge that comes their way. As independent professionals, we must not wait for someone to write a diagnosis for us. Examinations like these not only enhance our knowledge and skills but it also saves the therapist and his/her client a lot of time, helps strengthen the client- therapist relationship and helps in planning further treatment strategies.

References

• Human anatomy, B.D Chaurasia
• Human physiology for physio and occupational therapists, A.K Jain
• Dejong neurological examination

Thank you for reading