Cranial Nerves Lecture Notes PDF

RS3030 & RS5020 Cranial Nerves Dr Alex Cheung The Hong Kong Polytechnic University Copyright  Learning objectives  Identification of cranial nerves  Functions and pathways of cranial nerves  Clinical correlates: cond...

RS3030 & RS5020 Cranial Nerves Dr Alex Cheung The Hong Kong Polytechnic University Copyright  Learning objectives  Identification of cranial nerves  Functions and pathways of cranial nerves  Clinical correlates: conditions related to cranial nerve lesions Cranial Nerves Spinal Nerves  Cranial nerves: Anatomy  CN nuclei (cell bodies) are located in the brainstem and are considered to be part of CNS  CN (except I & II) begin exiting the brain at the Midbrain level and lead all the way down to Medulla  All CN can be seen from inferior brain except CN IV, which emerges from the posterior midbrain  Except CN I & II that have no peripheral component (I & II are myelinated by OD instead of SC), the axons and receptors of other CN exit the skull that belongs to peripheral nervous system  Sensory neurons of CNs are outside the brain, while the motor neurons are in brainstem Cranial nerves III-XII are emerging from brainstem CN III CN IV CN V CN VII CN VI CN VIII CN IX CN X CN XI CN XII Spinal Medulla Pons Midbrain Cord  Cranial nerves: Functions  Carry sensory, motor and autonomic information to and from the receptors of the HEAD, FACE, NECK & VISCERA – Receive information from somatosensory receptors (e.g. carry sensory message from the skin, tongue and muscles of the face) – Receive information from Special sense receptors (for vision, audition, olfaction, gustation) – Proprioception (e.g. temporomandibilar joint) – Supply motor innervations to muscles of the face, eyes, tongue, jaw and neck muscles – Parasympathetic regulation of viscera function & reflexes (e.g. pupil size, lens of the eyes)  Cranial Nerves (CN) Purely Sensory Mixed (Sensory & Motor) Purely Motor Olfactory N (I) Trigeminal (V) Oculomotor (III) Optic (II) Facial (VII) Trochlear (IV) Vestibulocochlear Glossopharyngeal (IX) Abducens (VI) (VIII) Vagus (X) Accessory (XI) Hypoglossal (XII) CN I: Olfactory nerve (sensory) CN I: Olfactory nerve Pathway: nasal chemoreceptors → olfactory bulb → Orbitofrontal cortex olfactory tract → 1° olfactory cortex (incl. Olfactory piriform cortex, amygdala, entorhinal cortex nerves etc) → 2 ° olfactory cortex (incl orbitofrontal cortex (or via thalamus), hippocampus etc) → hypothalamus → ANS response (e.g. appetite, salivation, gastric contraction) 1° olfactory cortex => recognizes odors and associates them with memories or emotional responses 2 ° olfactory cortex=> processes information about odors’ intensity, directionality, and duration. https://www.science.org/doi/10.1126/sageke.2006.5.pe6  Examination of Olfactory nerve (CN I) Eyes closed Test one olfactory nerve at a time by blocking the other nostril (usually with coffee, vanilla etc.) Injury of CN I (could be associate with infection, brain tumor, head trauma, epilepsy, URTIs, nasal and paranasal sinus diseases, multiple sclerosis, AD, PD, DM, COVID etc) may lead to: Anosmia Lesion symptoms: Hyposmia  Unilateral lesion: NO symptom (unaware) Hyperosmia Dysosmia (olfactory hallucinations)  Bilateral lesion: loss of sense of smell CN II: Optic nerve (sensory)  Eye & retina Retina is a thin transparent tissue that lines the back of the eye and is comprised of a number of layers Photoreceptors—rods: sensitive to dim light, forming images in grayscale Photoreceptor—cones: sensitive to high- intensity light, enabling colour vision Bipolar cells—second order neurons, gather info from photoreceptor cells and pass to ganglion cells Retinal ganglionic cells—multipolar, third order neuron with axons forming optic nerves; receive visual info directly or indirectly (amacrine cell) from bipolar cells (The Scientific Research Society, Research Triangle Park, NC.)  Optic nerves convey visual acuity (the accuracy of sight, not the interpretation of visual image) The visual pathway Left visual right visual from both eyes towards the optic chiasm field At optic chiasm, optic nerves carrying info from field nasal retina → cross to the contralateral side of the optic chiasm, while those conveying info from temporal retina stay ipsilaterally. After optic chiasm, the optic tract will go to either Nasal retina of the followings: i) Lateral Geniculate Nuclei (of thalamus) Temporal retina - Organize input from retina (~ post office) before Temporal retina Optic nerve sending to visual cortex (Brodmann’s area 17) Optic chiasm Signals from via optic radiations (or geniculo-calcarine tract) Ipsilateral temporal & Contralateral ii) Superior Collicui (Tectum) Lateral nasal retinae Geniculate Optic tract - Orientating movement of head and eye Nucleus iii) Pretectum (LGN) Hypothalamus - Reflex control of pupil and lens (CN III) Pretectum Superior iv) Hypothalamus colliculus - Circadian rhythm Optic radiations http://graphics.cs.cmu.edu/courses/16-899A/2014_spring/thevisualworld/3.pdf Visual cortex  Visual fields L R Lesions Total right in visual A. eye visual loss pathway Bitemporal B. hemianopia C A B Left nasal C. hemianopia E D D. Left homonymous hemianopia Left inferior E. quadrantopia https://commons.wikimedia.org/wiki/File:ERP_-_optic_cabling.jpg  Lesion Site Clinical Manifestations A Loss of vision of the right eye Damage to the optic nerve B Bitemporal hemianopia Damage in the optic chiasm – only the nasal retinal fibres – Loss of peripheral vision (stimulated by peripheral vision) cross (the temporal fibres remain in the optic tract and so are not damaged) C Left nasal hemianopia Damage at the optic nerve from the left temporal retina – Loss of nasal vision on the left hand side (receiving vision from left nasal field) D Left homonymous hemianopia Damage at left nasal and right – Loss of left peripheral and right nasal temporal fibres in the optic tract vision E Left inferior quandrantopia Damage at some optic radiations (e.g. in this case fibers – Specific loss of quadrants of visual field carrying lower left quadrant of both visual field) Optic nerve can be damaged by intracranial hypertension, or a variety of metabolic disorders (e.g. diabetes, vasculitis, multiple sclerosis) CN VIII: Vestibulocochlear nerve (sensory)  CN VIII: Vestibulocochlear Nerve (sensory) A sensory nerve consisting of 2 branches:  Cochlear branch: transmit information related to hearing from the cochlear  Vestibular branch: transmits information related to head position and head movement from the vestibular apparatus (semicircular canal & vestibule)→ provide awareness of body’s spatial orientation; and for balance control The structure of the ear Outer ear channel to receive sound wave and pass to tympanic membrane Middle ear three ear ossicles (stapes, incus, Tensor malleus) → convert sound wave into mechanical signal (pass to oval window) tympani Inner ear Convert mechanical energy into neural signal Translate head’s position and movement into neural signal Stapedius Auditory Sound wave→ through Scala vestibuli & Scala tympani→ Movement of perilymph system → vibration of basilar membrane → hair cells bends due to sliding with Tectorial membrane → hair cells depolarize→ send signals to spiral ganglion→ cochlear nerve  Organ of Corti-- Conversion of sound wave into neural signals Cochlear nerve Vestibular canal Cochlear duct Organ of Corti Cochlear Organ of Corti→ cochlear nuclei→ inferior Basilar duct colliculus → medial geniculate body→ membrane Tympanic Cochlear canal primary auditory cortex Tectorial membrane  Apex is sensitive to low frequency Base is sensitive to high frequency NEUROSCIENCE, 4th Ed, Fig 13.15 (Part 1) AUDITORY PATHWAY Provides Spiral Ganglion awareness & recognition of Ventral & Dorsal sounds Cochlear nuclei Integrate Superior Olive auditory Orients head & signals eyes toward / Inferior Colliculus MIDBRAIN sound Medial geniculate lateral lemniscus nucleus Locates sound source based on angle and Auditory Cortices at intensity the temporal lobe PONS (Brodmann 31, 32) Spiral Ganglion  DISORDERS OF AUDITORY SYSTEM Conductive deafness (common) Disruption of transmission of vibrations in outer / middle ear Causes: excessive wax, otitis media Sensorineural deafness (Peripheral Lesion) Damage of receptor cells / cochlear nerve Central Cause: Ménière’s Disease, acoustic neuroma (Ménière’s Disease → Tinnitus (ringing in the ear); hearing loss, vertigo, feeling of “fullness” in the ear) CNS deafness (Central Lesion) Peripheral Lesions at brain stem Lesions at cortical level Vestibular apparatus—semicircular canal The flow of endolymph fluid inside the three semicircular canals during head movements (angular) trigger movements of cilia of the hair cell at different ampulla Bending TOWARD the of the semicircular canal→ activating the kinocilium → Excitation respective vestibular nerves Bending AWAY from the kinocilium → Inhibition http://kin450-neurophysiology.wikispaces.com/VOR https://www.youtube.com/watch?v=UKaBZprL3t4 Upon left cervical rotation: L. horizontal canal activated R. horizontal canal inhibited Upon left cervical side-bending: L. posterior canal activated R. posterior canal inhibited Upon cervical flexion: L. superior canal activated R. superior canal activated https://www.youtube.com/watch?app=desktop&v=MMSG4cbNp_0 Vestibular apparatus—vestibule Utricle & Saccule Utricle—detect linear horizontal acceleration (e.g. forward-backward movement like in a car) & static horizontal head tilt Saccule—detect linear vertical acceleration (e.g. like in an elevator) & static vertical head tilt Linear acceleration and change in head position alter the flow of endolymph (otolith)→ detected by the hair cells of the macula → activating the respective vestibular nerves Utricle—sensitive to horizontal motion Saccule—sensitive to vertical motion  Examination of vestibulocochlear nerve (CN VIII) Supine roll test for horizontal BPPV Dix-Hallpike testing maneuver Benign paroxysmal positional vertigo (BPPV) https://www.youtube.com /watch?v=XSXwlUUpkow https://www.youtube.com/watch?v=-Yy71lf27J0 https://www.youtube.com/watch?v=FgF91K7dU8Y  CN III (Oculomotor nerve) (All motor) CN IV (Trochlear nerve) CN VI (Abducens nerve)  Control 6 extraocular muscles for eye movement  Coordination of two eyes  reflective constriction of the pupil and the muscle controlling the lens of the eye i.e. pupillary, consensual and accommodation reflex  Right eyeball The orbit Optic canal Where CN II passes through Superior orbital fissure where CN III CN IV CN VI pass through Infraorbital Infraorbital Maxilla groove foramen Left eyeball Right eye Superior Oblique (IV) Left eye Superior Rectus (III) Medial Rectus (III) Lateral Rectus (VI) Inferior Rectus (III) For Inferior Oblique (III) (III) opening eye lid Extraocular muscle (SO4LR6)3 innervation  Basic Eye Movements Elevation Adduction Intorsion Head rolls laterally Eyeball rolls medially Eyeball rolls laterally Head rolls Medially Depression Abduction Extorsion Right eye MR—adduct (in) LR—abduct (out) SR—elevate, adduct (in), intorsion IR—depress, adduct (in), extorsion SO—depress, abduct (out), intorsion IO—elevate, abduct (out), extorsion Pupillary (& accommodation) reflex is controlled by the intrinsic eye muscles of the iris (regulated by CN II & III) Ciliary muscle (Sym) (III) Sympathetic Parasympathetic Distant vision Close vision Dim light Bright light Pupils dilate Pupils constrict http://hyperphysics.phy-astr.gsu.edu/hbase/vision/accom.html  Pupillary light reflex pathway Light shined into one eye elicits Ciliary nerve reflexive constriction of both (innervate pupils (consensual reflex) pupillary sphincter, ciliary muscle, CN II convey sensory information cornea from the retina → Interneurons from the pretectal area → Oculomotor nerve Info send to Parasympathetic nucleus of CN III on both sides → ciliary ganglia/nerves → pupillary sphincter → pupil constriction  Accommodation reflex pathway A change in curvature of lens, contraction of pupil, & position of eye in response to viewing a near object CN II convey sensory information from the retina → Lateral Geniculate body → Visual Cortex → (i) Frontal eyefield of frontal cortex→ oculomotor nucleus → medial rectus contraction (ii) Pretectal area → CN III → ciliary ganglia/nerve → pupillary sphincter contraction (Lundy-Ekman 2012)  Cranial nerve reflex by CN III  Pupillary reflex: pupil constriction in the eye directly stimulated by the bright light  Consensual reflex: constriction of the pupil of the other eye  Accommodation: when viewing objects