Cranial Nerves Overview.pdf

Picture: https://www.britannica.com/science/cranial-nerve Cranial Nerves On Occasion Our Trusty Truck Acts Funny, Very Good Vehicle Any How I – Olfactory II – Optic III – Oculomotor IV...

Picture: https://www.britannica.com/science/cranial-nerve Cranial Nerves On Occasion Our Trusty Truck Acts Funny, Very Good Vehicle Any How I – Olfactory II – Optic III – Oculomotor IV – Trochlear V – Trigeminal VI – Abducens VII – Facial VIII – Vestibulochlear IX – Glossopharyngeal X – Vagus XI – Accessory XII - Hypoglossal  Some Say Marry Money But My Brother Says Big Brains Matter More Cranial I: Sensory Cranial II: Sensory Cranial III: Motor Cranial IV: Motor Cranial V: Both (sensory & motor) Cranial VI: Motor Cranial VII: Both (sensory & motor) Cranial VIII: Sensory Cranial IX: Both (sensory & motor) Cranial X: Both (sensory & motor) Cranial XI: Motor Cranial XII: Motor Cranial Nerves Overview Mnemonic for cranial nerves: "On Occasion Our Trusty Truck Acts Funny, Very Good Vehicle Any How" Twelve pairs of cranial nerves, each with distinct functions and pathways. Classification of Cranial Nerves Mnemonic for sensory/motor/both: "Some Say Marry Money But My Brother Says Big Brains Matter More" Cranial Nerves I & II: Sensory Cranial Nerves III, IV, VI, XI, XII: Motor Cranial Nerve V: Both (sensory & motor) Cranial Nerves VII, IX, X: Both (sensory & motor) Cranial Nerve VIII: Sensory Olfactory Nerve (I) Function: Responsible for the sense of smell Directly attached to the forebrain and linked to the limbic system. I – Olfactory nerve Attached directly to forebrain Closely associated with Limbic system Optic Nerve (II) Function: Transmits visual information from the retina to the brain. Tests: Visual field, colour vision (Ishihara), visual acuity (Snellen), papillary response. II - Optic Attached directly to forebrain Impulses from the retina to the brain Visual field testing Colour vision test (Ishihara) Visual acuity (Snellen) Papillary response Oculomotor Nerve (III) Innervates extrinsic and intrinsic eye muscles. Involved in eyelid elevation, pupillary constriction, and accommodation. Cranial nerve palsy causes include trauma, demyelinating diseases, and increased intracranial pressure. Generally These nerves Somatic Innervate Also III – Oculomotor, taken together all have a role to play in eye motor neurones extraocular muscles – eye preganglionic parasympathe IV – Trochlear, movement movement tic neurones and innervate the extrinsic VI - Abducens muscles of the eye Control smooth muscle of the eye  Oculomotor Nerve (III) Role: Innervates extrinsic eye muscles Raise eyelid Innervates intrinsic eye muscles – pupillary constriction and accommodation Cranial (Third) nerve palsy Uncommon Mortality and morbidity is dependant on the underlying cause Ie subarachnoid haemorrhage, meningitis, neoplasm Cause: Direct trauma Demyelinating disease (ie MS) Increased intracranial pressure Space-occupying lesion Spontaneous subarachnoid haemorrhage Microvascular disease (ie diabetes) Microvascular disease (ie giant cell arteritis) https://ebmnerd.com/cranial-nerve-3-palsy/ Trochlear Nerve (IV) Function: Controls superior oblique muscle for lateral/inferior gaze. Unique for emerging from the dorsal aspect of the brain stem. Damage leads to diplopia and compensatory head tilting away from the affected side.  Trochlear nerve (IV) Role: Motor nerve Innervates single muscle – superior oblique muscle Lateral/inferior gaze Only cranial nerve to emerge from the dorsal aspect of the brain stem Single IV lesion – Rare – common cause trauma to orbit Signs of single IV lesion Diplopia due to weakness and downward and inward eye movement Compensate – tilting head away form affected side http://www.clinicalexams.co.uk/4th-cranial-nerve-tests-for-the-trochlear-nerve/ Abducens Nerve (VI) Function: Innervates lateral rectus muscle for outward gaze. Lesions manifest as an inability to look laterally. Common causes of dysfunction include multiple sclerosis (MS) and pontine cerebral vascular accidents (CVA). Abducen nerve (VI) Role: Motor nerve Movement of lateral rectus muscle Outwards (lateral) gaze Signs of single IV lesion Inability to look laterally Causes MS, pontine CVA https://www.neurologyneeds.com/neuroanatomy/cranial-nerves/nvi-abducens-nerve/  Combined III, IV and VI lesions CVA Tumours, Wernicke's encephalopathy, Aneurysms, MS, Myasthenia gravis, Meningitis, Muscular dystrophy, Myotonic dystrophy, Cavernous sinus thrombosis, GBS, Cranial arteritis, Trauma and orbital pathology. Trigeminal Nerve (V) Mixed function: Sensory for facial sensation and motor for chewing muscles. Sensory branches split into three: ophthalmic, maxillary, and mandibular. Key tests: Palpation of muscles, corneal reflex response, sharp/dull sensation evaluation. Has a motor & sensory component: Motor - Muscles of chewing (mastication) V - Trigeminal Sensory - Facial sensation (split into 3)  https://www.drugs.com/cg/trigeminal-neuralgia.html Motor Assessment: Palpate Masseter & temporalis muscles Open mouth against resistance Sensory: Sharp & dull sensation in nerve distribution Reflex: Corneal reflex – Blink response to light touch (cotton, tissue) of cornea Facial Nerve (VII) Mixed function: Motor for facial expressions, sensory for taste in the anterior 2/3 of the tongue. Assessments include observing nasolabial folds and taste testing with various substances. Bell’s Palsy can affect muscle control.  Motor: Inspect nasolabial folds Can the patient raise their eyebrows, close the eyes tight or blow out the cheeks (forehead sparing = Upper Motor Lesion UMN) VII - Facial Sensory: Taste in the anterior 2/3 of the tongue. Usually ask about sense of taste or can be tested with sugar, salt, vinegar https://www.sciencedirect.com/topics/neuroscience/nerve-to-the-stapedius Motor functions LEFT diagram – which muscles are innoverted. RIGHT diagram – sensory nerve for taste The chorda tympani branch of the facial nerve is responsible for innervating the anterior 2/3 of the tongue with the special sense of taste.  Bell’s Palsy The muscles of facial expression will be paralysed or severely weakened. The other symptoms produced depend on the location of the lesion, and the branches that are affected: Chorda tympani – reduced salivation and loss of taste on the ipsilateral 2/3 of the tongue. Nerve to stapedius – ipsilateral hyperacusis (hypersensitive to sound). Greater petrosal nerve – ipsilateral reduced lacrimal fluid production. The most common cause of an intracranial lesion of the facial nerve is middle ear pathology – such as a tumour or infection. If no definitive cause can be found then the disease is termed Bell’s palsy. Extracranial Lesions Extracranial lesions occur during the extracranial course of the facial nerve (distal to the stylomastoid foramen). Only the motor function of the facial nerve is affected, therefore resulting in paralysis or severe weakness of the muscles of facial expression. There are various causes of extracranial lesions of the facial nerve: Parotid gland pathology – e.g a tumour, parotitis, surgery. Infection of the nerve – particularly by the herpes virus. Compression during forceps delivery – the neonatal mastoid process is not fully developed, and does not provide complete protection of the nerve. Idiopathic – If no definitive cause can be found then the disease is termed Bell’s palsy. Vestibulocochlear Nerve (VIII) Function: Involved in hearing and balance. Basic tests include Weber’s and Rinne’s tests for auditory acuity. Hearing, balance & equilibrium: Simple tests of auditory acuity Weber’s test – tuning fork on top of head. Conduction = Lateralized to VIII - impaired side. Sensorial = Lateralized to good ear. Normal = Vestibulocohlear Mid-line Rinne’s test – Compare air conduction to bone conduction (in normal conditions air is better than bone conduction From the pons Glossopharyngeal Nerve (IX) & Vagus Nerve (X) Work together to control swallowing and the pharynx/larynx. Uvula elevation test: Asymmetry indicates lesion on the opposite side. Vagus nerve also has autonomic functions affecting heart rate and digestion.  Generally assessed together and work together to control pharynx, larynx and swallow: Uvula elevation – Say “Ahhhh” If it moves to one side = X Lesion on the opposite side IX – Glossopharyngeal, X - Vagus Vocal quality Gag reflex Taste – Posterior 1/3 of tongue (sugar, salt, vinegar) Glossopharyngeal nerve https://medical-dictionary.thefreedictionary.com/glossopharyngeal+nerve It is important to know these 2 (see next oage)  ‘Wandering’ nerve Left and right asymmetry Accessory Nerve (XI) Function: Innervates sternocleidomastoid and trapezius muscles. Assessment involves shoulder shrugging and head turning against resistance. Innervation of the sternocleidomastoid and trapezius muscles Ask the patient to shrug their shoulders against resistance XI - Accessory (trapezius) Ask the patient to turn head from side to side against resistance (sternocleidomastoid)  Accessory nerve https://medical-dictionary.thefreedictionary.com/accessory+nerve Hypoglossal Nerve (XII) Function: Controls tongue movements. Deviations indicate lesions on the affected side, and inspection can show atrophy or fasciculations. “Stick your tongue out and move it side to side” Inspect the tongue – Fasiculations, atrophy (lower motor neuron LMN) XII - Hypoglossal Deviation to one side usually indicates lesion on the side to which the tongue is deviated Hypoglossal nerve https://www.pinterest.com/pin/320670435941971784/ Picture: https://br.pinterest.com/pin/537476536762145864/