In this episode we'll be covering the cranial nerve portion of the neurological examination. Before beginning any assessment, we need to prepare. And the mnemonic WIPE helps us remember the main steps.
This involves washing our hands and wiping down any equipment, introducing ourselves to the patient and confirming their identity, Obtaining permission to perform the exam, including roughly what it will entail, and positioning the patient as well as appropriately exposing them. In this case, that's sitting upright with a head and neck exposed. Objects and equipment you need to fully perform the exam include a Snellen's visual acuity chart, pen torch, a sharp object like a Neurotip, a tuning fork and a glass of water.
the cranial nerves themselves provide an organised structure to follow as they are numbered from one to twelve two useful mnemonics to know to remember the names and the general function of each are o o o to touch and feel very good velvet such heaven represents the olfactory optic oculomotor trochlear trigeminal abducens facial vestibular cochlea glossopharyngeal, vagus, spinal accessory and hyperglossal nerves. With the mnemonic, some say marry money, but my brother says big brains matter more. To help remember, sensory, motor or both. The patient is inspected generally before looking at specific nerve functions. This includes looking for any obvious facial asymmetry or speech disturbances, strabismus, meaning misalignment of the visual axis of the eyes, as well as any abnormal posturing or objects such as glasses or hearing aids.
The first cranial nerve is the olfactory nerve, responsible for the transmission of signals related to smell, otherwise known as olfaction. It is an entirely sensory nerve and generally this is tested informally by asking the patient if they have noticed any changes in their sense of smell. however, can be assessed by using smelling bottles. Loss of smell, termed anosmia, can be seen in COVID-19, an early sign of Parkinson's disease, head trauma, as the fibres of the olfactory nerve travel through the cribriform plate, which is a thin portion of the ethmoid bone that is prone to fractures.
Nasal blockage can also be a cause, therefore the nostrils should be inspected if the patient complains of anosmia. The second cranial nerve is the optic nerve, responsible for transmitting visual information and as such is responsible for sight. Like the olfactory nerve, it is also entirely sensory.
Visual acuity, that is the clarity of eyesight, is formally assessed with a Snellen's chart, but in practice may informally be assessed by asking the patient to read words on a name badge. If the acuity is too poor for this, Then move down to counting fingers and light perception. Be sure to ask the patient to wear their glasses if they use any prior to testing.
Visual fields are tested by comparing your own visual fields to those of the patient, assuming yours are normal. This is done by sitting opposite the patient and asking them to cover one of their eyes, for example the left eye, and then fixating on your face, while you cover your opposite eye. so in this case the right eye.
Central field loss can be screened for by asking the patient if they see any part of your face is distorted and to test the visual field hold an arm out laterally and position your finger so that it is halfway between you and the patient in terms of distance, just out of sight. Then move your hand in from the periphery of your vision towards the center and ask the patient when they see it. If they are unable to see it while you can, then there may be a deficit in the field. This is repeated for each quadrant.
Fields can be tested more specifically using perimetry. Visual neglect can also be tested for by uncovering both eyes and again asking the patient to fixate on your face. Then while holding your hands out laterally, move your fingers asking the patient to point to the ones that are moving. And in cases of neglect, they may not recognise the fingers moving on one particular side. The pupils should be inspected, noting the shape as normally they are circular.
and for any discrepancy in size between the two sides, called anisochoria. Several reflexes are tested here using a pen torch. It's important to remember in pupil reactions, the optic nerve carries sensory afferent fibers from the retina. Those are fibers carrying sensory information to the central nervous system, specifically to the ipsilateral pre-tectal nucleus.
From there, E-ferent fibres, meaning those carrying motor information from the CNS, project to the eddinger westfall nuclei on both sides, then on to the iris sphincter muscle via the ocular motor nerve, causing pupillary constriction. Altogether, this means sensory information from one eye causes both eyes to respond to it. The direct reflex, which is where when light is shone into a pupil, that same pupil constricts.
The consensual reflex, which is where when light is shone into one pupil, the contralateral pupil constricts. And the accommodation reflex, which is when asking the patient to focus on a distant object, then switching to a closer object, for example your finger, the pupils should constrict as the eyes converge. The swinging light test involves swinging the light between both pupils. We normally expect that in response to light in either eye both pupils will equally constrict however when the afferent limb is damaged in one eye then the pupils dilate slightly when light is shone into the affected eye this is known as a relative afferent pupillary defect or marcus gunn pupil caused by retinal damage such as detachment or optic neuropathy from neuritis compression by structures like tumours or unilateral glaucoma. An efference defect would cause a pupil that does not constrict when either eye is exposed to light.
This is often due to oculomotor palsy, which we'll cover shortly. Note that the afferent component is intact here, so light shining into the affected eye would still cause constriction in the contralateral pupil. We've touched a bit on testing the third cranial nerve, the oculomotor nerve. and will cover the trochlear and abducens, so 4th and 6th cranial nerves here, as well as their functions are linked. As the name suggests, the oculomotor nerve is involved in the control of movement of the eyes, and it transmits entirely motor information.
As we've mentioned, it carries fibres causing pupillary constriction, and also for the levator palpebrae superioris muscle, that elevates the upper eyelid. It's responsible for movement of most extraocular muscles, but there are two exceptions. The superior oblique muscle is responsible for abducting and depressing the eye, as well as internally rotating the eye, which is innervated by the trochlear nerve, and the lateral rectus is innervated by the abducens nerve, responsible for abducting the eye. To test them, ask the patient to fixate on your finger and have them keep their head still.
while following the finger as you draw out a H shape to assess each axis of eye movement. Abnormality is suggested by restriction in eye movement or diplopia meaning double vision. Oculomotor nerve palsy can feature midriasis, remember D for dilatation of the pupil, ptosis meaning drooping of the upper eyelid, and a typically down and out eye gaze because the superior oblique and lateral rectus muscles remain intact therefore moving the eye down and out. Trochlear nerve palsy leads to vertical diplopia worsened by looking inferiorly and abducens nerve palsy causing horizontal diplopia worsened when looking towards the affected side. The fifth cranial nerve is the trigeminal nerve that has both sensory and motor function.
It's split into three branches. The ophthalmic, maxillary and mandibular branches that provide sensory transmission for approximately the upper, middle and lower third of the face respectively, tested by touching each district of the nerve and confirming equal sensation. The mandibular branch also transmits motor information to the muscles of mastication. They are the muscles involved in chewing and grinding such as the temporalis, masseter, lateral, temporalis, lateral, lateral, temporalis, lateral, temporalis, and medial pterygoid muscles.
These are assessed by inspecting for wasting, palpating superiorly and inferiorly to the zygomatic arch to feel the temporalis and masseter contractions respectively. while asking the patient to clench the jaw, and asking them to move the jaw from side to side. The reflexes to be tested here include the corneal reflex, where the cornea is lightly brushed with cotton wool, testing the afferent function of the ophthalmic trigeminal branch and the efferent coming from the facial nerve, causing the patient to blink bilaterally. Jaw jerk is another reflex, testing afferents of the mandibular branch and efference of the trigeminal nerve.
By lightly tapping on the chin with the mouth slightly open, looking for an upwards jerking of the jaw, an excessive response can close the mouth and is associated with upper motor neuron lesions. Cranial nerve 7 is the facial nerve that has motor and sensory function. The sensory function is transmission of taste sensation from the anterior two thirds of the tongue and this is assessed. by asking for any changes in taste and it also provides sensory information to a section of scalp posterior to the ear.
Its motor function involves signaling to the muscles of facial expression. To test these, ask the patient to raise their eyebrows, testing the function of the frontalis muscle, scrunch their eyes closed, testing the orbicular oculi muscles, puff out their cheeks, testing the orbicular oris muscle, and smiles showing their teeth testing the levator anguliores and zygomaticus major muscles. It also provides innovation to the stapedius, a muscle involved in stabilising the stapes bone in the ear and regulating sound, disturbance of which can lead to hyperacusis.
It also provides innovation to mucous glands of the mouth, nose and pharynx, as well as the salivary and lacrimal glands. Importantly, the lower 1 third has unilateral innervation, while the upper 2 thirds of the face has bilateral innervation from the CNS. This means upper motor neuron lesions like strokes will have facial palsy deficits on the lower 1 third, but the upper 2 thirds will have some compensation, while lower motor neuron deficits will lead to the entire affected side drooping, like in Bell's palsy.
The vestibulocochlear nerve is the 8th cranial nerve, purely sensory in function and specifically involved in hearing and balance. General screening involves asking the patient if they have noticed any change in their hearing, which can be crudely tested by whispering a number or word into their ear from around 60cm, while covering the other. With Rene's and Weber's tests being slightly more formal assessments. Next up.
at cranial nerve 9, the glossopharyngeal nerve and cranial nerve 10, the vagus nerve, both of which have sensory and motor functions. The sensory function of the glossopharyngeal nerve is conveying sensation of taste from the posterior one third of the tongue and also the afferent portion of the gag reflex. Motor function is to the stylopharyngeus muscle that elevates the pharynx in speech and swallowing. The sensory function of the vagus nerve involves the posterior portion of the external auditory canal and ear and has numerous visceral sensory involvements that include the heart and gastrointestinal tract its motor functions include most of the muscles of the pharynx responsible for the initiation of swallowing and for speech as well as most of the muscles of the soft palate to test these assess for any voice hoarseness or quietness and ask the patient to say ah with an open mouth and look for symmetrical elevation of the pharynx and also ask them to cough as vagal lesions can lead to impaired cough production.
Asking the patient to swallow a small amount of water also tests the afferent limb from the glossopharyngeal nerve and the efferent limb from the vagus nerve. The gag reflex may be elicited but it's not comfortable and so is not routinely done. The 11th cranial nerve is known as the spinal accessory nerve, involved in motor function of the sternocleidomastoid and trapezius muscles, which can be tested by inspecting for any wasting and asking the patient to turn their head against resistance and shrug their shoulders respectively. Then we have the 12th and final cranial nerve, which is the hypoglossal nerve, that has motor function only, involving the extrinsic muscles of the tongue. To test it, Inspect for any asymmetry or fasciculations of the tongue.
and ask the patient to protrude it, looking for any deviation, which is typically towards the affected side in lower motor neuron injuries. To test power, ask the patient to press the tongue against each cheek. To conclude, thank the patient and summarise your findings.
Further assessments can include neurological exams of the limbs and potentially investigations such as imaging or audiometry.