1-CNs

• Cranial Nerves


  • CN I: Olfactory
  • CN II: Optic
  • CN III: Oculomotor
  • CN IV: Trochlear
  • CN V: Trigeminal
  • CN VI: Abducent
  • CN VII: Facial
  • CN VIII: Vestibulocochlear
  • CN IX: Glossopharyngeal
  • CN X: Vagus
  • CN XI: Accessory
  • CN XII: Hypoglossal
• CN I: Olfactory


  Function: serves the sense of smell
• CN I: Olfactory


  • Type of lesions affecting the nerve: tumors on the floor of the anterior fossa, head injury, and Alzheimer
  • Effect of the lesions: Anosmia

  
• CN II: Optic


  Function: vision
• CN II: Optic


  • Type of lesions: Diabetes, ischemic neuropathy (microvascular), demyelination (e.g. multiple sclerosis), viral (measles, mumps), nerve compression and occlusion (e.g. giant cell arteritis), trauma, optic nerve glioma, vit B def, drugs and toxins (e.g. amiodarone, ethambutol, quinine, tobacco, and methyl alcohol), optic neuritis, raised ICP, papilledema, and severe anemia
  • Effect of the lesions: unilateral visual loss starting as central or paracentral scotoma (an area of depressed vision within the visual field) is characteristic of optic nerve lesions
• Visual field defects and sites of lesions


  • Paracentral scotoma: Retinal lesion
  • Monocular field loss: Optic nerve lesion
  • Bitemporal hemianopia: Chiasmal lesion
  • Homonymous hemianopia: Optic tract lesion
  • Homonymous quadrantanopia: Temporal lesion
  • Homonymous quadrantanopia: Parietal lesion
  • Homonymous hemianopia: Occipital cortex or optic radiation
  • Homonymous hemianopia: Occipital pole lesion
• CN III: Oculomotor


  Function: 1. innervates all extraocular muscles except superior oblique and lateral rectus. 2. Provides preganglionic parasympathetic fibers to ciliary ganglion, which in turn supplies constrictor pupillae and ciliary muscles of eyeball.

  
• CN III: Oculomotor


  • Type of lesions: Diabetes, posterior communicating artery aneurysm, giant cell arteritis, raised ICP, uncal herniation, and syphilis
  • Effect of the lesions: unilateral complete ptosis, the eye faces down and out, and the pupil is dilated and is fixed to light and convergence (frequently the lesion is partial, particularly in diabetes mellitus, when parasympathetic fibers are spared, and the pupil reacts normally)
• Differentiate between ptosis associated with CN III palsy and Horner syndrome


  • CN III palsy: severe ptosis, normal/dilated pupil, eye position down and out
  • Horner syndrome: mild ptosis, constricted pupil, normal eye position

  
• CN IV: Trochlear


  Function: innervates the Superior oblique muscle (normally depresses eye & moves it laterally) – mnemonic: SO4
• CN IV: Trochlear


  • Type of lesions: Head injury (trauma to orbit) or congenital
  • Effect of the lesions: Torsional diplopia (two objects at an angle) when looking down (e.g. when walking down the stairs), eye looks up and inward, and head tilted away from lesion
• CN VI: Abducent


  Function: innervates the Lateral rectus muscle (normally move eye laterally; abductor) – mnemonic: LR6
• CN VI: Abducent


  • Type of lesions: Diabetes, MS, pontine CVA, infiltration by tumor, cavernous sinus thrombosis, and if bilateral must rule out high ICP
  • Effect of the lesions: Can't look laterally (eye can't be abducted beyond midline), in primary position the unopposed pull of the medial rectus muscle causes the eye to turn inward (medial squint/ strabismus), Horizontal diplopia/ double vision (worse when looking at site of lesion)

  
• CN V: Trigeminal


  Function: it has both motor (innervates muscles of mastication and tenser tympani muscle) and sensory functions (Skin of the Face and scalp, cornea, mucosa of the oral cavity and nasal cavity, anterior 2/3 of the tongue, and Teeth)
• CN V: Trigeminal


  • Type of lesions: pathology within the brainstem (infarct, tumor, syringobulbia, or MS) , at the cerebellopontine angle (acoustic neuroma), within the petrous temporal bone(spreading middle ear infection) , or within the cavernous sinus (aneurysm of the internal carotid artery, tumor, thrombosis) & skull base pathology
  • Effect of lesions: complete fifth nerve lesion on one side causes unilateral sensory loss of the face, tongue and buccal mucosa, paralysis of muscles of mastication, jaw deviates to side of lesion when the mouth is opened, brisk jaw jerk, and diminution of the corneal reflex (often the first sign of fifth nerve lesion)

  
• Trigeminal neuralgia (Tic douloureux)


  This condition is seen most commonly in old age and is almost always unilateral. Presentation: severe paroxysms of knife-like pain that occur in one or more sensory divisions of the trigeminal nerve (rarely ophthalmic division). Each paroxysm is stereotyped, brought on by stimulation of specific trigger zone in the face (e.g. washing, shaving, and eating). Diagnosis is based on the history as there are no objective physical signs. Management: Anticonvulsant carbamazepine suppresses attacks in most patients, Phenytoin and gabapentin are also used but are less effective, if drugs fail, thermocoagulation of the trigeminal ganglion or section of the sensory division may be necessary.
• CN VII: Facial


  Function: 1. Sensory: Taste from anterior 2/3 of tongue (Through chordae tympani branch). 2. Motor: innervates muscles of facial expression, stapedius muscle (the nerve to the stapedius muscle has a damping effect to protect the ear from load noise), posterior belly of digastric, and stylohyoid muscle. 3. Secretomotor parasympathetic fibers to submandibular, sublingual, nasal and palatine gland.

  
• Types of facial nerve lesions


  • UMN: Site of lesions above the nucleus in the pons, Type of lesions - Stroke, Tumors, Multiple sclerosis
  • LMN: Site of lesions in the pons or in the pathway from pons to its exist, Type of lesions - Bell's palsy (HSV, corneal scarring), Ramsay hunt syndrome (herpes), Lyme, Polio, Skull fracture (temporal bone), Parotid and Cerebellopontine angle tumors, Otitis media, Gullian barre, DM, Sarcoidosis, Pons tumor/ infarction

  
• Facial nerve lesions


  • Involvement of the forehead: UMN - Patients can make furrows on looking upward as the forehead is spared because of bilateral cortical innervation of neurons supplying the upper face, LMN - Forehead is involved and furrows are absent on looking upwards of the affected side of the face
  • Effect of the lesions: UMN - paralysis of CONTRALATERAL LOWER face, Forehead is spared, Contralateral lip sags and the angle of the mouth falls and dribbling occurs, ipsilateral lip pulled up normally, LMN - Paralysis of whole face and forehead IPSILATERALLY, Ipsilateral lip sags and the angle of the mouth falls and dribbling occurs, Eye remains open à irritation, dry, tears over face, and risk of ulceration to the cornea, Damage to the nerve at the temporal bone may be associated with loss of taste from anterior 2/3 of tongue and undue sensitivity to sounds
  • Association with hemiplegia: UMN - Invariably associated, LMN - May be associated
  • Epidemiology: UMN - Isolated involvement of this type is rare, LMN - Isolated involvement of this type is common

  
• CN VIII: Vestibulocochlear


  Function: has two components: Vestibular - innervates Vestibule and semicircular canals of inner ear and accounts for equilibrium, Cochlear nerve - innervates Cochlea of inner ear and accounts for hearing
• CN VIII: Vestibulocochlear


  • Type of lesions: brainstem pathology, cerebellopontine angle (acoustic neuroma), and petrous temporal bone (trauma, middle ear infection, tumors)
  • Effect of the lesions: Vestibular nerve --> vertigo and vomiting (nystagmus and ataxia are the principle physical signs), Cochlear nerve--> sensorineural deafness and tinnitus

  
• CN IX: Glossopharyngeal


  Function: 1. Sensory: taste from posterior 1/3 of tongue, general sensations from pharynx, tonsillar sinus, pharyngotympanic tube, and middle ear cavity. 2. Motor: innervates Stylopharyngeus muscle 3. Secretomotor fibers to parotid gland (through otic ganglion).

  
• CN IX: Glossopharyngeal


  • Type of lesions: brainstem lesions and deep laceration in the neck
  • Effect of the lesions: loss of the taste of the posterior one third of the tongue and loss of sensation on the affected site of the soft palate

  
• CN X: Vagus


  Function: Sensory: general sensations from pharynx, larynx, tracheobronchial tree, lungs, heart and Gastrointestinal tract (up to left colic flexure), Motor: palate, pharynx, larynx, trachea, bronchial tree, heart, Gastrointestinal tract (up to left colic flexure)
• CN X: Vagus


  • Effect of lesions disturbing the nerve: Palate weakness à palate & uvula deviates AWAY from lesion

  
• CN XI: Accessory


  Function: Motor to Sternocleidomastoid and trapezius muscles
• CN XI: Accessory


  • Type of lesions: laceration of the neck
  • Effect of the lesions: paralysis of the Sternocleidomastoid and the descending fibers of trapezius muscle; drooping of the shoulder
• CN XII: Hypoglossal


  Function: Motor to the intrinsic and extrinsic muscles of the tongue (Except palatoglossus muscle)
• CN XII: Hypoglossal


  • Effect of the lesions disturbing the nerve: Ipsilateral tongue weakness à tongue deviates TOWARDS lesion upon protrusion

  
• Bulbar palsy vs Pseudobulbar palsy

  • Bulbar palsy: Motor neuron lesion (Lower motor neuron lesion), Affected CN9 - 12, Type of lesions - Motor neuron disease, syringobulbia, GBS, poliomyelitis, Symptoms - Dysarthria, dysphagia, nasal regurgitation, Tongue - Atrophy, weak, wasted, fasciculation, Gag reflex - None, Jaw reflex - none
  • Pseudobulbar palsy: Upper motor neuron lesion, Affected CN9 - 12 (Corticobulbar tract), Type of lesions - Motor neuron disease, cerebrovascular disease (typically after multiple infarcts), multiple sclerosis, Symptoms - Dysarthria, dysphagia, nasal regurgitation, Tongue - Small and spastic with no fasciculation, Gag reflex - Exaggerated, Jaw reflex - exaggerated

  
• Pupillary light reflex


  Afferent: CN 2 (signals from light to brain), Efferent: CN 3 (constricts pupils in response to light)

  
• Corneal reflex


  Afferent: CN 5 (ophthalmic division of trigeminal), Efferent: CN 7 (muscles of facial expression)