CRANIAL NERVE SYSTEM
Position the patient sitting over the edge of the bed
Look at the head, face and neck
Inspection
Craniotomy scars
Ptosis – drooping of the upper eyelid
The first [Olfactory] Nerve
Purely sensory nerve
This nerve is not tested routinely, ask patient have they any difficuty with their sense of smell. If the answer is no, move to the second cranial nerve.
If patient c/o loss of smell [anosmia] test each nostril separately with bottles containing essences of familiar smells such as coffee.
The second [Optic] Nerve
Purely sensory nerve which begins in the retina
Visual acuity is tested with the patient wearing his or her glasses
Ask patient do they have any difficulty with their vision
“Can you see the clock on the wall?”
“Can you read the newspaper?”
Each eye should be tested separately
A portable Snellen’s chart will enable you to perform a more formal test
A patient who is having visual problems should be asked to count fingers held up in front of each eye in turn, and if this is not possible then perception of hand movement should be assessed. Failing this light perception only may be present.
Visual fields are assessed by positioning yourself in visual confrontation about a metre away. Always remove the patient’s glasses. Test the visual fields of your patient against your own.
Ask patient to cover his right eye with his right hand and close your left eye
Ask patient to “keep looking at my eye”
Test his left temporal vision against your right temporal vision by moving your wagging finger from the periphery towards the centre
“Tell me when you see my finger move”
The temporal field should be tested in the horizontal plane and in the upper and lower temporal quadrants.
Change hands and repeat on the nasal side
Any areas of field defect are mapped out
The visual fields of his right eye are assessed in the same way.
Bitemporal hemianopia: optic chiasm lesion, pituitory tumour
Unilateral field loss: optic nerve lesion, tumour/vascular
Homonymous hemianopia: optic tract to occipital cortex, vascular/tumour
The blind spot – there is a small area close to the centre of the visual fields where there is no vision. This is the area where the optic disc is seen on fundoscopy and is the point where the optic nerve joins the retina.
The blind spot enlarges with papilloedema e.g. raised intracranial pressure with brain tumour
Central scotoma – or loss of central macular vision is tested for with a red–headed hat pin.
Move the red-headed pin from the temporal periphery through the central field to the nasal periphery, asking the patient “can you see the head of the pin?”
E.g. demyelination of the optic nerve in multiple sclerosis can cause loss of central vision
Colour vision – Tests of colour vision are not carried out routinely
They may reveal subtle defects of the retina or optic nerve
Ishihara plates are used. Checking patient’s eyes separately plates made up of coloured dots containing numerical shapes are presented to patient who is asked to discern the numbers shown in each pattern.
Fundoscopy – Use the right eye to look in patient’s right eye and vice versa
Look first at the cornea, iris and lens. Then look at the fundus.
Search first for the optic disc then look at the four quadrants of the retina
The Third [Oculomotor], Fourth [Trochlear] and Sixth [Abducens]
The pupils
The size of the pupils depends on a balance of parasympathetic and sympathetic innervation. The parasympathetic innervation of the eye is supplied by the Edinger-Westphal nucleus of the third nerve [stimulation causes pupillary constriction]
The pupillary reflexes depend on the optic nerve for their afferent limb
Ask the patient to look at an object at an intermediate distance
Examine the pupils for size, shape, equality and regularity
Light reflex: with a pocket torch shine the light from the side [so the patient does not focus on the light and accomadate] into one of the pupils to assess its reaction to light
Normally the pupil into which the light is shone constricts briskly this is the direct light reflex
Simultaneously the other pupil constricts in the same way, this is the consensual light reflex
Repeat this procedure on the other side
Afferent pupillary defect/Marcus Gunn pupillary sign: Move the torch from pupil to pupil
If an eye has optic atrophy or severely reduced visual acuity from another cause the affected pupil will dilate paradoxically after a short time
This occurs because afferent impulses are reduced so the light reflex is markedly reduced in the eye with decreased acuity
Accomodation: Ask the patient to look into the distance and then to focus on your finger held near the patient’s nose
There is normally constriction of both pupils, the accomodation response
Absent light reflex with an intact accomodation reflex occurs in Argyll Robertson pupil in syphilus affecting the nervous system
Eye movements
Assess for eye movement, diplopia [double vision] and nystagmus
“Look at my finger; follow it with your eyes”
Ask the patient to look laterally left and right, continue moving the finger to complete H pattern.
Tell the patient to inform you if they see double images [diplopia]
Diplopia is an early sign of ocular muscle weakness
The third nerve supplies all the ocular muscles except;
- Superior oblique – fourth nerve
- Lateral rectus – sixth nerve
The lateral rectus and medial rectus abduct and adduct the eyes
When the eye is abducted the elevator is the superior rectus [third nerve] while the depressor is the inferior rectus [third nerve].
When the eye is adducted the elevator is the inferior oblique [third nerve] while the depressor is the superior oblique [fourth nerve]
Third nerve also supplies Levator palpebrae superioris
The false image is usually paler, less distinct and more peripheral than the real one
Features of a third nerve lesion
- Complete ptosis
- Eye down and out
- Dilated pupil which is not responsive to light and accomodation
Features of fourth nerve lesion
- Usually associated with a third nerve palsy
- Double vision going down stairs
- Ask patient to turn the eye in and then to look down
- Superior oblique paralysis
Features of sixth nerve lesion
- Failure of lateral movement
- Nystagmus
Ask patient to follow your finger to each side
The direction of nystagnus is defined as that of the fast [correcting] movement
- Vestibular lesion – nystagmus away from the side of the lesion
- Cerebellar lesion – nystagmus to the side of the lesion
Internuclear ophthalmoplegia – abducting eye has greater nystagmus than the adducting eye. There is dissociation of conjugate eye movements.
It suggests MS with a lesion in the medial longitudinal bundle
The fifth [trigeminal] nerve
This nerve contains both sensory and motor fibres
There are 3 sensory divisions
- Ophthalmic: supplies forehead, cornea and conjunctiva
- Maxillary: supplies the middle of the face
- Mandibular: supplies the lower jaw
Facial sensation
Test in the three divisions of the nerve comparing each side with the other
- FOREHEAD - Ophthalmic
- MAXILLA - Maxillary
- LOWER JAW – Mandibular
Test for pain using sharp object.
Ask patient does it feel sharp or dull.
Test for light touch using cotton wool
The patient should be instructed to say “yes” each time the touch of the cotton wool is felt. Do not stroke the skin touch it.
Motor division
Inspect for wasting of the temporal and masseter muscles
Ask patient to clench their teeth and palpate for contraction of the temporal and masseter muscles
Ask patient to open their mouth and hold it open while the examiner attempts to force it shut [pterygoid muscles]. A unilateral weakness of the motor division causes the jaw to deviate towards the weak side.
If weakness is suspected patients should be asked to move the jaw laterally against resistance. The jaw can be moved towards the affected muscle but cannot move towards the normal side.
Jaw jerk
The afferent and efferent pathways are supplied by the fifth nerve
The patient lets his mouth fall open slightly
The examiners finger is placed on the jaw
The finger is tapped lightly with a tendon hammer
The reflex response comprises brisk closure of the jaw
It is often not visible and can be difficult to determine if it is present
Corneal reflex
The afferent part of the reflex arc is the first division [ophthalmic nerve] of the fifth nerve
The efferent arc is supplied by facial nerve
Each fifth nerve communicates with both seventh nerves and therefore both eyes close when each cornea is stimulated
Lightly touch the cornea with a wisp of cottonwool
Reflex blinking of both eyes is a normal response
The seventh [facial] nerve
Supplies: The muscles of facial expression
Stapedius muscle
Chorda tympani contains taste fibres from anterior two-thirds of the tongue
Inspection: for facial asymmetry
Unilateral drooping of the corner of the mouth
Smoothing of the wrinkled forehead
Smoothing of the nasolabial fold
Muscle power
Ask patient to look up and wrinkle his forehead
Feel for muscle strength by pushing down on forehead
This movement is preserved on the side of an upper motor neurone lesion [a lesion which occurs above the level of the brainstem nucleus], because of bilateral cortical representation of these muscles
The remaining muscles of facial expression are usually affected on the side of an UMN lesion.
In a LMN lesion all muscles of facial expression are affected on the side of the lesion.
Ask the patient to shut the eyes tightly
Observe and try to force open each eye
Ask the patient blow out cheeks
Ask the patient to show their teeth
Compare the nasolabial grooves which are smooth on the weak side
If a lower motor neuron lesion is detected [weakness on one side of face], check for ear and palatal vesicles of herpes zoster of the geniculate ganglion – the Ramsay Hunt syndrome
Examining for taste of the anterior two-thirds of the tongue is not usually required
**Left upper motor neuron seventh nerve lesion leads to drooping of the corner of the mouth, flattened nasolabial fold, and sparing of the forehead on the left side**
The Eighth [Vestibulocochlear] nerve
There are two components:
- Vestibular containing afferent fibres for balance
- Cochlear with afferent fibres for hearing
Examination for hearing
Ask the patient do they have any problems with their hearing
Cover one of the patient’s ears with your hand and whisper into the other ear
If deafness is suspected perform Rinne’s test and Weber’s test
1. Rinne’s test
A vibrating tuning fork is placed on the mastoid process behind the ear. When the sound is no longer heard it is placed in line with the external meatus. Normally the sound is audible at the external meatus. With nerve deafness the note is audible at the external meatus, as air and bone conduction are reduced equally, so that air conduction is better as is normal. This is termed Rinne-positive.
With conduction [middle ear] deafness no note is audible at the external meatus. This is termed Rinne-negative.
2. Weber’s test
A vibrating tuning fork is placed on the centre of the forehead. Normally the sound is heard in the centre of the forehead. With nerve deafness the sound is transmitted to the normal ear. With conduction deafness the sound is heard louder in the abnormal ear.
3. Audiometry
Patients with defective hearing should be referred for audiometry. This measures the degree of hearing loss at different sound frequencies.
Examination of vestibular function
This cannot effectively be evaluated at the bedside.
The ninth [Glossopharyngeal] and Tenth [Vagus] nerves
Get the patient to open their mouth and inspect the palate with a torch. Note any displacement of the uvula. Ask the patient to say ‘Ah’. If the uvula is drawn to one side this indicates a unilateral tenth nerve palsy. The uvula is pulled towards the normal side.
Now test gently for the gag reflex
• Ninth is the sensory component
• Tenth is the motor component
Touch the back of the pharynx on each side with a spatula. Ask the patient if the touch of the spatula is felt each time. Normally there is reflex contraction of the soft palate.
The ninth nerve supplies taste from the posterior two-thirds of the tongue this is not routinely tested for.
The eleventh [Accessory] nerve
It supplies motor fibres to the trapezius and sternomastoid muscles
Ask the patient to shrug their shoulders and feel the bulk of the trapezius muscles and attempt to push the shoulders down.
Ask the patient to turn their head against resistance and feel the bulk of the sternomastoids. Feel for the sternomastoid on the side opposite to the turned head. There will be weakness on turning the head away from the side of a muscle whose strength is impaired.
The twelfth [Hypoglossal] nerve
It is the motor nerve for the tongue
Inspect for wasting and fasciculations. These indicate a lower motor neurone lesion
Ask the patient to stick out their tongue. It will deviate towards the weaker side if there is a unilateral lower motor neuron lesion.
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