Cranial nerves Flashcards
What makes up a cranial nerve exam
General inspection
Assessment of each cranial nerve
General inspection
Speech abnormalities: may indicate glossopharyngeal or vagus nerve pathology.
Facial asymmetry: suggestive of facial nerve palsy.
Eyelid abnormalities: ptosis may indicate oculomotor nerve pathology.
Pupillary abnormalities: mydriasis occurs in oculomotor nerve palsy.
Strabismus: may indicate oculomotor, trochlear or abducens nerve palsy.
Limbs: pay attention to the patient’s arms and legs as they enter the room and take a seat noting any abnormalities (e.g. spasticity, weakness, wasting, tremor, fasciculation) which may suggest the presence of a neurological syndrome).
Look for objects or equipment on or around the patient that may provide useful insights into their medical history and current clinical status:
Walking aids: gait issues are associated with a wide range of neurological pathology including Parkinson’s disease, stroke, cerebellar disease and myasthenia gravis.
Hearing aids: often worn by patients with vestibulocochlear nerve issues (e.g. Meniere’s disease).
Visual aids: the use of visual prisms or occluders may indicate underlying strabismus.
Prescriptions: prescribing charts or personal prescriptions can provide useful information about the patient’s recent medications.
Cranial nerves
1- Olfactory (S)
2- Optic nerve (S)
3- Oculomotor (M) PARASYMPATHETIC
4- Trochlea (M)
5- Trigeminal (B)
6- Abducens (M)
7- Facial (B) PARASYMPATHETIC
8- Vestibulocochlear (S)
9- Glossopharngeal (B) PARASYMPATHETIC
10- Vagus (B) PARASYMPATHETIC
11- Accessory (M)
12- Hypoglossal (M)
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Olfactory nerve (CN1) Foramen and fissure (F&F)
Foramen/Fissure – Cribriform plate
Function – sense of smell
Sensory
CN1 test and outcomes
Ask Pt: How they noticed any changes in their sense of smell? If no ask about taste to confirm, more of a recognisable loss.
Smell test - use different odours (Citrus, mint or coffee). Unilateral test – cover 1 nostril and patient closes their eyes)
Outcomes –
Anosmia – Complete loss of smell due to olfactory nerve damage (Genetics, Parkinsons, fracture of the Cribriform plate, SOL.)
Parosmia – Distorted sense of smell (bacterial or viral infections)
Hyperosmia – overwhelming sensitivity to smells (migraine, genetics, Epilepsy)
Optic nerve (CN2) F&F
Foramen/Fissure – Optic foramen
Function – Sight
Sensory
CN2 Tets
Visual acuity - Snellen wall chart (Unilateral test). Patient covers one eye and reads down the chart until the 6th line if possible.
Visual fields test - Practioner covers opposite eye to patient. Starting with the right eye (patient) using your left arm take it into the periphery and flex your first digit. Pt should be staring at a fixed point (i.e your nose). Following that, with the same eye, use you right arm, perform the same process. Then switch eyes.
Pupillary reflexes - Patient will cover the mid point in their face creating a divide between the eyes. Shine the light in one eye and observe bi-lateral constriction. Progress then to ‘swinging light test’. Patient will need to focus on a point in front of them, not directly the light.
CN2 outcomes
Visual acuity - If the patient reads the 6/6 line but gets two letters incorrect, you would record as 6/6 (-2). Could be due to age related muscular degeneration or optic neuritis
Visual fields - Information from the L optic nerve from the L medial field (Nasal field) towards the chiasm but remains on the same side before heading to the visual cortex via the L geniculate body. Information from the L optic nerve from the R lateral field (temporal field) heads towards the chiasm and desiccates and heads towards the L geniculate body. Due to the nature of the anatomy, results can be confusing.
Pupillary reflex - Direct response suggests the optic nerve is receiving information and the oculomotor nerve is constricting the pupil. Consensual response but no direct response suggests that the optic nerve is receiving the signal but the oculomotor is failing to constrict the pupil. Absent pupillary reflex suggest the optic nerve is not recognising the stimulus. Relative afferent pupillary defect, optic nerves is damaged, both pupils will constrict less when light is shone into the affected eye compared to the healthy eye (large retinal detachment or optic neuritis)
If a defect is found – refer to an optician.
Oculomotor nerve (CN3)
Foramen/Fissure - Superior orbital fissure
Function – The oculomotor nerve supplies all extraocular muscles except the superior oblique (CN4) and the lateral rectus (CN6)
Motor
PARASYMPATHETIC – Pupillary reflex
Elevation of the upper eyelid
CN3 tests and outcomes
H-Test
Light pupillary reflex - Ask the patient to focus on a target approximately half a metre away whilst you shine a pen torch towards both eyes.Inspect the corneal reflex on each eye: If the ocular alignment is normal, the light reflex will be positioned centrally and symmetrically in each pupil. Deflection of the corneal light reflex in one eye suggests a misalignment.
Outcomes –
Ptosis (Innervation to the levator palpebrae superioris) - (Horner’s syndrome, Myasthenia gravis, muscle damage)
Down and out (Divergent squint)
Pupil dilation
Eye movements restricted
Trochlea Nerve (CN4) F&F
F Foramen/Fissure - Superior orbital fissure
Function - Innervates the superior oblique (ability to look down).
Motor
CN4 Test and outcomes
H-Test
Outcomes - Vertical diplopia - when looking inferiorly, due to loss of the superior oblique’s action of pulling the eye downwards
Diplopia common when going downstairs or reading when palsied.
Trigeminal nerve (CN5) F&F
Foramen/Fissure:
Ophthalmic (Superior orbital fissure)
Maxillary (Foramen Rotundum)
Mandibular (Foramen Ovale)
Both sensory and motor
Function –
O - Sensory to scalp, forehead, nose and upper eyelid.
Mx – Sensory to palate, upper jaw, upper teeth, lower eyelid and nasal cavity
Ma – Sensory to lower lip, lower teeth, anterior 2/3 of tongue, lateral cheek, temporal region. Motor to muscles of mastication, digastric, mylohyoid and the middle ear.
CN5 tests
Sharp and soft sensory test. (Pin & cotton wool) V1,V2,V3) - should be performed in all 3 regions. To ensure the patient understands what is normal, place the cotton wool/pin prick on their sternum or hand for reference. Patient closes eyes and states “sharp” or “soft”. Need to be able to visualise the three separations of the trigeminal nerve:
Mastication test (V3) - Ask the patient to chew. Encourage them to move from left to right or in a circular motion. Palpate the temporalis, masseter and pterygoids.
Jaw reflex - Place your left index finger on their chin and striking it with a tendon hammer. This should cause slight protrusion of the jaw. Brisk jaw jerk could be sign of bilateral UMN lesion
Corneal reflex
CN5 outcomes
Loss of sensation
Loss of distinction between sharp and soft
Weakness or inability to masticate
increased reflex (mouth closing)
Loss of blinking reflex
Trigeminal neuralgia - sudden, severe facial pain. It’s often described as a sharp shooting pain or like having an electric shock in the jaw, teeth or gums.
Often associated with MS.
