Cranial Nerves PDF

HUMAN DISEASE: Neurology 2 Cranial Nerves Introduction – There are 12 cranial nerves – Part of the peripheral nervous system (PNS) – Primarily sensory and/or motor supply to the head and neck – Dental Relevance - Innervation to all head and neck structures of relevance to dentists - Cranial nerve pa...

HUMAN DISEASE: Neurology 2 Cranial Nerves Introduction – There are 12 cranial nerves – Part of the peripheral nervous system (PNS) – Primarily sensory and/or motor supply to the head and neck – Dental Relevance - Innervation to all head and neck structures of relevance to dentists - Cranial nerve pathology may be detected during routine dental examination, or patients may present with symptoms - If you suspect cranial nerve pathology, ensure there is appropriate medical follow-up (e.g. usually via GP, A&E for emergencies) The 12 Cranial nerves I Olfactory II Optic III Occulomotor IV Trochlear V Trigeminal VI Abducens VII Facial VIII Vestibulocochlear IX Glossopharyngeal X Vagus XI Accessory XII Hypoglossal I OLFACTORY - Shortest cranial nerve; unmyelinated; sensory component only Specialised epithelium at the top of the nasal cavity contains olfactory nerve fibres Function: sense of smell - Damage to the olfactory nerve can cause altered sense of smell, or complete loss of sense of smell (anosmia) - Causes include head injuries, tumours and neurodegenerative disorders - (Temporary changes to smell can be caused by infection) Testing: 1. Ask about any recent changes to sense of smell 2. Then, with the patient’s eyes closed, ask them to occlude one nostril and identify the smell (e.g. coffee, vanilla). Repeat on the other side. II Optic - Sensory component only - Function: transmission of sensory information from the retina to the primary visual cortex of the brain - Causes of optic nerve defects – Trauma – Tumour (e.g. pituitary adenoma) – Multiple sclerosis (optic neuritis) – Stroke II Optic Examination includes testing the following - Visual acuity - Visual fields - Pupillary reflexes - Fundoscopy* * Fundoscopy is performed with an ophthalmoscope. It allows visualisation of the retina and optic disc (optic nerve head). In a dental setting, fundoscopy is rarely performed; however visual acuity, visual fields and reflexes can be performed easily. II Optic Visual acuity Formal: Snellen chart with the patient sat 6 metres away. Colour vision is also assessed using Ishihara plates Dental setting: Ask the patient to read from a printed page (glasses, contact lenses should be worn). Test one eye at a time. Visual fields Tested through confrontation Assumes that the examiner has normal visual fields Monocular blindness (e.g. trauma) Bitemporal hemianopia (classically seen in acromegaly) N.B. The darker blue lines on the diagram to the left relate to the temporal field of vision Homonymous hemianopia (e.g. stroke) II Optic Pupillary Reflex Darkened room 1.Direct reflex – shine pen torch into one eye. Look for pupillary constriction of ipsilateral eye (i.e. the eye you are shining the light into) 2.Consensual reflex – shine the light into the same eye as previously, but this time, observe the contralateral eye for pupillary constriction 3.Now repeat for the other eye (direct and consensual reflex) What is being tested: Afferent (sensory) pathway - optic nerve Efferent (motor) pathway - oculomotor nerve Other tests performed in a medical setting: accommodation, swinging light test II Optic - examples of nerve defects Left optic nerve lesion Left oculomotor nerve lesion: Shine a pen torch into the left eye: Shine a pen torch into the left eye: -Left direct reflex lost (the left pupil will not constrict) -Left consensual reflex maintained (left pupil will constrict when light shone in the right eye) -Right direct pupillary response is maintained -Right consensual reflex is lost (right pupil will not constrict when light is shone into left eye) - Left direct reflex lost - Left consensual reflex lost - Right direct reflex maintained - Right consensual reflex maintained III/IV/VI III Oculomotor nerve IV Trochlear nerve VI Abducens nerve All have a motor function and supply the extra-ocular muscles III/IV/VI - Oculomotor (III) – supplies medial, superior & inferior rectus. inferior oblique, levator palpebrae superioris. Also supplies parasympathetic fibres involved in pupillary constriction - Trochlear (IV) – supplies superior oblique - Abducens (VI) – supplies lateral rectus Remembered using the formula: SO4LR6 III/IV/VI Palsies of III, IV or VI will result in diplopia III Causes of palsy: diabetes, increased intra-cranial pressure Eye is fixed down and out, unless looking towards the affected side Additional signs: ptosis, dilated pupil (mydriasis) IV Causes of palsy: trauma Eye cannot move down and in (vertical diplopia when looking inferiorly) VI Causes of palsy: stroke, multiple sclerosis Cannot look to the affected side Testing: Usually performed alongside cranial nerve II, after visual fields. Ask the patient to follow a pen as you draw out the letter H. Ensure they keep the head still and only move the eyes. V Trigeminal nerve - Motor and sensory function - Causes of V nerve palsy: - Upper motor neurone lesions (i.e. within the brain cortex) include tumours, multiple sclerosis - Lower motor neurone lesions (affecting the peripheral nerve fibres) include cavernous sinus lesions, iatrogenic damage to IAN/lingual nerve V Trigeminal nerve Testing: - Sensory component divided into ophthalmic (V1), maxillary (V2) and mandibular (V3) divisions - Tested through light touch and pin prick (use a Neurotip) - Corneal reflex (V1) not routinely tested - Motor component supplies muscles of mastication - Inspect temporalis/masseter for wasting - Palpate temporalis/masseter muscle bulk with patient clenching - Ask the patient to open the jaw against resistance from your hand - (Jaw jerk reflex – not routinely performed) VII Facial nerve - Sensory for taste to the anterior 2/3rds via chorda tympani - Motor to the muscles of facial expression, nerve to stapedius. - Secretomotor to lacrimal, submandibular & sublingual salivary glands. VII Facial nerve - Causes of VII nerve palsy - Upper motor neurone lesions: stroke - Lower motor neurone lesions: Bell’s palsy, parotid tumour - Remember that in lower motor neurone lesions the entire half of the face is affected. - In upper motor neurone lesions, the forehead is spared (as there is bilateral innervation from the cortex) Testing: - - alsoofsensfnations > Ask about changes to sense of taste - Ask about hearing (hyperacusis) - Facial movements (tested against resistance) - - clear Bell's louder polsy sounds Raise eyebrows, close eyelids, puff out cheeks purse the lips, show your teeth VIII Vestibulocochlear nerve - Sensory function - Involved in hearing and balance - Causes of VIII nerve defects: acoustic neuroma, Paget’s disease - Testing: - Ask about changes to hearing - Whisper into the ear (choose a bi-digit number or two syllable word) and ask the patient to repeat - Rinne and Weber test are performed using a tuning fork to assess for sensorineural vs conductive deafness IX Glossopharyngeal nerve - Sensory and motor functions - Principle role is sensory to tonsillar fossa and pharynx; taste to the posterior 1/3rd of the tongue and parasympathetic innervation to the parotid glands. - Causes of IX nerve palsy: trauma, tumour, diphtheria (IX nerve problems usually occur alongside CN X problems) - Patients with IX nerve palsy will have impaired gag reflex - Testing the gag reflex is not routinely performed X Vagus nerve - Motor function supplying the pharynx, larynx and soft palate - Causes of X nerve palsy: trauma, brainstem lesion - Test: ask the patient to say ‘ah’ to visualise the uvula and soft palate. If a deficit is present, the uvula will deviate towards the unaffected side - Gag reflex (not performed routinely) NB The vagus nerve has other important functions, including visceral sensation of the heart, and parasympathetic innervation of the gastrointestinal tract and heart rhythm. XI Accessory nerve - Motor function - Also known as the ‘spinal accessory’ nerve - Causes of XI nerve palsy: stroke - Test: - Inspect for wasting of trapezius/sternocleidomastoid - Shrug shoulder against resistance (test one side at a time) - Turn the head against resistance XII Hypoglossal nerve - Motor function to the tongue - Causes of XII nerve palsy: trauma, brainstem lesions - Test: ask the patient to protrude their tongue - The tongue should look symmetrical and there should not be any deviation on protrusion. - If a lesion is present, the tongue deviates to the side of the lesion. - There may also be muscle wasting on the side of the lesion and fasiculation (involuntary twitching) Performing a Cranial Nerve Examination - Within a dental setting we tend to perform an abbreviated form of the cranial nerve examination (e.g. the eye examination is not as in depth as in a medical setting) - Practice is important as there is a lot to remember (practice with each other initially so that you do things correctly. Once you have a clear idea of the structure, recruit friends and relatives to practice with to improve your fluency) - Online videos can be useful, but may contain errors. The links below are not perfect, but are some of the better examples of free online videos - University of Leicester https://www.youtube.com/watch?v=jdaq-Ecz7Co - Geeky Medics https://geekymedics.com/cranial-nerve-exam/ - Macleod’s Clinical Examination is a textbook that provides excellent examination videos (check the library). They are much more detailed than you need, but everything is performed correctly. Acknowledgements and further reading Acknowledgements: Professor Richard Cook for original slides References: Teachmeanatomy.com for images Greenwood M, Meechan J. General medicine and surgery for dental practitioners Part 4: Neurological disorders. BDJ, 2003 https://www.nature.com/articles/4810275 (this excellent article is free and provides a broad overview of neurology for the dental setting) Any questions: please contact [email protected]