RCSI Cranial Nerves I-VI (PDF)

RCSI Royal College of Surgeons in Ireland Coláiste Ríoga na Máinleá in Éirinn Cranial nerves I-VI (incl. optical pathway/lesion and visual reflexes) Class Year 2 Semester 1 Course Medicine Lecturer Dr. Vijayalakshmi S B Date 19/11/2024 LEARNING OUTCOMES 1. Describe the visual p...

RCSI Royal College of Surgeons in Ireland Coláiste Ríoga na Máinleá in Éirinn Cranial nerves I-VI (incl. optical pathway/lesion and visual reflexes) Class Year 2 Semester 1 Course Medicine Lecturer Dr. Vijayalakshmi S B Date 19/11/2024 LEARNING OUTCOMES 1. Describe the visual pathway and its potential lesions 2. Compare and contrast the pupillary light and accommodation reflexes 3. Describe the corneal reflex 4. Discuss common pathologies causing visual disturbances (raised intracranial pressure, strabismus) 5. Describe cranial nerves I-VI, their nuclei, components and courses 6. Describe foramina, relations and functions of the cranial nerves I-VI 7. Discuss the effects of lesions to the cranial nerves I-VI 8. Outline testing the cranial nerves I-VI  Cranial nerves Twelve pairs: The first two, i.e., Olfactory & Optic are outgrowths from the forebrain and not actually part of the PNS but are counted as cranial nerves  Cranial nerves - origin Early brain development Secondary vesicles Cranial nerves – emergence from CNS Cranial nerves – emergence from CNS Cranial nerves – functional components TYPE Type of Innervation Structures innervated Cranial nerves Somatic Motor Somatic striated muscles Eyeball and tongue muscles CNs 3, 4, 6 and 12 (GSE) Branchial motor Motor innervation to skeletal Muscles of mastication, Facial CNs V3/Vc, 7, 9, 10 & 11 (SVE/BE) muscles derived from pharyngeal muscles, Muscles of Pharynx, (branchial) arches Larynx and palate Visceral motor Secretomotor (Parasympathetic) Lacrimal, Salivary glands, CNs 3, 7, 9 and 10 (GVE) Ciliary and sphincter pupillae muscles, Heart, Lungs and GI organs Somatic sensory General somatic sensation (Pain From the face and TMJ CN 5 (three divisions); (GSA) & temp., touch & pressure, 7, 9 & 10 Proprioception Visceral sensory Sensory input from viscera CNs 9 and 10 (GVA) Special sensory Smell, vision, taste, sound and Nose, Eyeball, Tongue, Ear CNs 1, 2, 7, 8, 9 and 10 (SA) balance  Motor cranial nerves Somatic motor (General somatic efferent-GSE) CN III, IV, VI, XII eyeball, eyelid, and tongue Branchiomotor (Special visceral efferent-SVE) CN Vc, VII, IX, X, XI e.g., mastication, facial expression Parasympathetic (General visceral efferent-GVE) CN III, VII, IX, X smooth muscle, heart muscle ciliary muscles of the eye secretomotor (glands)  Sensory cranial nerves Somatic sensory – Perception of touch, pain, temperature (General somatic afferent-GSA) Trigeminal nuclei (x 3); Cell bodies in various ganglia CNs V, VII, IX, X Special visceral sensory (Special afferent (SA)/Special visceral afferent (SVA) Nucleus Solitarius (for taste) Cell bodies in various ganglia (Smell, vision, sound, balance) CNs I, II, VII, VIII, IX, X Visceral sensory – Sensory input from viscera (General visceral afferent-GVA) CNs IX, X  Olfactory nerve – (I) Special sensory – smell (loss = anosmia) Olfactory/neuroepithelium in the roof of the nasal cavity 1st order neurons begin here – Olfactory neurons (bipolar) Olfactory nerve – (I)  Optic nerve – (II) Special sensory - vision  Photoreceptors and bipolar cells Primary – Bipolar cells of the retina - take Layers of the retina stimulus from photoreceptors Secondary – Ganglion cells send axons in the optic nerve - Decussation is partial – in the Light optic chiasm Tertiary–cell bodies in the lateral geniculate nucleus (thalamus) and project to the cortex Light https://www.researchgate.net/figure/The-basic- retinal-structure-Histological-appearance-of-choroid- and-retinal-layers-The_fig1_318758129 https://gene.vision/retina/  Ganglion cells and optic nerve Primary – Bipolar cells of the retina - take stimulus from photoreceptors Secondary – Ganglion cells send axons in the optic nerve - Decussation is partial – in the optic chiasm Tertiary–cell bodies in the lateral geniculate nucleus (thalamus) and project to the cortex  Optic chiasm and optic tract Primary – Bipolar cells of the retina - take stimulus from photoreceptors Secondary – Ganglion cells send axons in the optic nerve - Decussation is partial – in the optic chiasm Tertiary–cell bodies in the lateral geniculate nucleus (thalamus) and project to the cortex  Lateral geniculate and optic radiation Primary – Bipolar cells of the retina - take stimulus from photoreceptors Secondary – Ganglion cells send axons in the optic nerve - Decussation is partial – in the optic chiasm Tertiary–cell bodies in the lateral geniculate nucleus (thalamus) and project to the cortex https://clinicalgate.com/functional-neuroanatomy/  Projection to visual cortex Primary – Bipolar cells of the retina - take stimulus from photoreceptors Secondary – Ganglion cells send axons in the optic nerve - Decussation is partial – in the optic chiasm Tertiary–cell bodies in the lateral geniculate nucleus (thalamus) and project to the cortex 17: Primary visual cortex https://www.researchgate.net/figure/Visual-cortical-areas-including-Brodmann- Area-17-primary-visual-cortex-Brodmann-Area_fig2_306248282 Potential damages of the optic pathway OPTIC NERVE: monocular blindness OPTIC CHIASMA: bitemporal hemianopia (Tunnel vision) OPTIC TRACT & RADIATION: homonymous hemianopia  Oculomotor – (III) Eye movement: Voluntary ocular muscles (GSE) Parasympathetic supply (GVE) Right eye superior view lateral view https://www.brainkart.com/article/Muscles-of-the-Eyeball---Structure-of-the-Eye_14940/ Oculomotor – Voluntary ocular muscles  Oculomotor – Parasympathetic action Edinger-Westphal nucleus Parasympathetic oculomotor nucleus Synapse Ciliary ganglion → Accommodation → Pupillary constriction https://www.aao.org/bcscsnippetdetail.aspx?id=df4f4653-8109-4982-9421-b50c27ede8a9 https://d45jl3w9libvn.cloudfront.net/jaypee/static/books/9789350254974/Chapters/im ages/411-1.jpg  Oculomotor – Accommodation Accommodation is the adaptation of the eye to look at near objects 1. Change in the curvature of the lens (increases for nearby objects) The Ciliary muscle constricts, which relaxes the suspensory ligament, which is usually tense, maintaining the lens flat. When the suspensory ligament is relaxed, the curvature of the lens increases 2. The pupil constricts The Edinger Westphal nucleus signals the constrictor pupillae to constrict, this sharpens images on the retina 3. Convergence of the eye The Medial rectus contracts, causing the eye to move medially  Clinical aspects Edinger-Westphal nucleus Parasympathetic oculomotor nucleus Synapse Ciliary ganglion → Accommodation → Pupillary constriction https://quizlet.com/210930871/vi-vision-flash-cards/ Oculomotor – Pupillary Light reflex  Clinical aspects Achromatopsia - loss of colour perception Visual agnosia - impairment in recognizing visually presented objects, despite otherwise normal visual field, acuity, colour vision, language, and memory (corpus callosum lesion – objects in the left visual field cannot be named – connection to language centres lost) Prosopagnosia - a neurological disorder characterized by the inability to recognise faces Argyll Robertson pupil - pupillary light reflex lost, accommodation reflex present – neurosyphilis, lesion in pretectal nucleus Trochlear (IV) and Abducens (VI) Action of III, IV, & VI on eye movements Clinical examination of eye movements Action Clinical Examination Abduct first Lateral Medial Temporal Nose Adduct first  Lesions of III, IV and of VI Right Oculomotor nerve paralysis Right trochlear nerve paralysis Gaze – down and out, with pupillary dilation Right eye drifts upward → will have a drooping eyelid, too Head tilting to compensate for the strabismus and/or double vision Left abducens paralysis Left eye not abducting TRIGEMINAL NERVE  Introduction Largest cranial nerve Mixed nerve – contains both sensory and motor fibers It is motor to the muscles of the jaw area It receives sensory input from the greater part of the head and is connected with the trigeminal ganglion Peripheral processes of the ganglion cells form ophthalmic (V1), maxillary (V2) and mandibular (V3) divisions and the central processes form the sensory root  Trigeminal Nuclei Four nuclei: Main sensory nucleus – lies in the posterior part of the pons, receives the discriminative touch fibers of first-order neurons from the trigeminal ganglion through the sensory root Spinal nucleus – extends through the whole length of the medulla and into the upper part of the spinal cord as far as the second cervical segment and receives first-order sensory neurons for pain and temperature sensations Mesencephalic nucleus – composed of unipolar nerve cells situated in the central grey matter of the midbrain. Receives first sensory neurons for proprioceptive sensations Motor nucleus – situated in the pons medial to the main sensory nucleus Trigeminal Nuclei  Trigeminal ganglion (semilunar/gasserian/gasser’s ganglion) In the middle cranial fossa, the sensory root expands into the trigeminal ganglion, which contains cell bodies for sensory neurons in the trigeminal nerve. Semilunar in shape, which lies within the pouch of duramater called the trigeminal or Meckel’s cave Arising from the anterior border of the trigeminal ganglion are the three terminal divisions of the trigeminal nerve: – Ophthalmic division – Maxillary division – Mandibular division MECKEL’S CAVITY AND TRIGEMINAL GANGLION 35 Trigeminal ganglion To sensory nuclei Superior a orbital fissure c b Foramen Foramen rotundum ovale To muscles of mastication/ swallowing 36 Sensory Territories – Somatic sensory Trigeminal – Somatic sensory Mesencephalic nucleus Chief sensory nucleus Spinal tract & nucleus Trigeminal – Somatic sensory  Trigeminal – Branchiomotor (Vc) Mandibular nerve Muscles of mastication First pharyngeal arch Mylohyoid Motor nucleus lies in pons Anterior belly of digastric (adjacent to main sensory nucleus) Tensor veli palatini Tensor tympani  Corneal reflex NB Caution – if the eye has lost sensation, it may be damaged easily!!!  PRACTICE REFERENCES QUESTIONS