University of Northern Philippines College of Medicine, Batch 2026 Cranial Nerves PDF

UNIVERSITY OF NORTHERN PHILIPPINES NEUROSCIENCE 1A LC6 COLLEGE OF MEDICINE, BATCH 2026 TOPIC NAME: Cranial Nerves Transcribers: Sto....

UNIVERSITY OF NORTHERN PHILIPPINES NEUROSCIENCE 1A LC6 COLLEGE OF MEDICINE, BATCH 2026 TOPIC NAME: Cranial Nerves Transcribers: Sto. Domingo, Sudayon, Sulit Dr. Crispin Allan Viado | Oct. 2022 Editors: Tan, Viloria OUTLINE Figure 1: Different Cranial Nerves I. INTRODUCTION TO CRANIAL NERVES Table 1: Cranial Nerves and its Function II. PURELY SENSORY CRANIAL NERVES CRANIAL Common Name Mnemonic Function Mnemonic A. CN I – OLFACTORY NERVE NERVE B. CN II – OPTIC NERVE I Olfactory Oh Sensory Some C. CN VIII – VESTIBULOCOCHLEAR NERVE II Optic Oh Sensory Say III. PURELY MOTOR CRANIAL NERVES III Oculomotor Oh Motor Money A. CN III IV Trochlear To Motor Matters B. CN IV V Trigeminal Touch Both But C. CN VI VI Abducent And Motor My D. CN XI VII Facial Feel Both Brother E. CN XII VIII Vestibulocochlear Very Sensory Says IV. MIXED CRANIAL NERVES IX Glossopharyngeal Good Both Big A. CN V X Vagus Velvet Both Brains B. CN VII XI Accessory Ahh Motor Matter C. CN IX XII Hypoglossal Heaven Motor More D. CN X FORAMINA OF THE CRANIAL VAULT I. Introduction to Cranial Nerves Cranial nerve exit foramina in summary Anterior Fossa: Cranial Nerves o I - perforations in cribriform plate 12 pairs, Roman numerals I to XII Middle Fossa: All passes through foramina in base of skull (Foramen magnum - largest o II – optic foramen foramina) o III, IV, VI and ophthalmic division of V – superior orbital fissure Mainly control anatomic structures of the head except: "Frozen eye" - tumor in the superior orbital fissure o Vagus (X) – extends into the thoracic (controls the heart) and o Maxillary division of V – foramen rotundum abdominal cavities (controls abdominal organs) o Mandibular division of V – foramen ovale o Accessory (XI) – Controls Sternocleidomastoid and Trapezius (the Posterior Fossa: one that turns the head from right to left or shrugging of the o VII and VIII – internal auditory meatus shoulders) o IX, X and XI – jugular foramen All arise from the brainstem (Nuclei) EXCEPT CN I and II o XII – hypoglossal foramen Cranial Nerves Nuclei (Nerve Cell Body/Soma Origin) Cranial nerves are collection of axons. Most cranial nerves emerge from the brainstem except I and II CN I: Basal forebrain CN II: Diencephalon (Thalamus) CN III – XI: Brainstem Figure 2: Different Exit Foramina in the Cranium SOMATIC vs. VISCERAL FUCNTIONS A. Sensory Division 1. Somatic Sensory – Skeletal Muscles ▪ General – Touch, pain, pressure, vibration, temperature, proprioception in skin, body wall and limbs ▪ Special – Hearing, equilibrium, vision, smell 2. Visceral Sensory – Smooth Muscles and Glands ▪ General – Stretch, pain, temp., chemical changes, and irritation in viscera; nausea and hunger ▪ Special – Taste Page 1 of 25 [NEUROSCIENCE 1A] 1.05 CRANIAL NERVES – Dr. Crispin Allan Viado B. Motor Division ▪ Example of Bilateral Motor Cortex Control: 1. Somatic Motor Accessory Nerve ▪ General - Motor innervation of all skeletal muscles The motor cortex sends control to both Sternocleidomastoid and 2. Visceral Motor Contralateral Trapezius ▪ General – motor innervation of smooth and cardiac muscle, o Motor cortex damage will present with weakness to contralateral glands; equivalent to Autonomic Nervous System (ANS) trapezius and bilateral sternocleidomastoid (that means if there is (parasympathetic and sympathetic division) damage on the right cortex, there will be difficulty turning the neck on both sides) Damage to the Accessory nerve itself – present with Ipsilateral weakness/ paralysis on both muscles. Table 2: UMN vs LMN SIGN UMN Lesions LMN Lesions Weakness Yes Yes Atrophy No* Yes Fasciculations No Yes Reflexes Increased** Decreased Tone Increased** Decreased *Mild atrophy may develop due to disuse ** With Acute UMN lesions; tone may be decreased 2. Somato-Sensory o 3 neuron pathways o Afferent pathway o Via Sensory Ganglia: Figure 3. Visceral Motor a. Semilunar ganglion (V)/ Trigeminal ganglion b. Geniculate ganglion (VII) Cranial Nerves Overview c. Vestibular and Cochlear ganglia (VIII) Overview: d. Glossopharyngeal Nerve ganglia (IX) Somato-motor e. Vagus nerve ganglion (X) Somato-sensory o Somato-sensory innervation: Viscero-motor a. Primary neuron: Cranial Nerve Ganglia Viscero-sensory b. Secondary neuron: Brainstem Special sensory (smell, sight, taste, hearing, balance c. Tertiary neuron: Thalamus SOMATOMOTOR FUNCTIONS: Part of the Pyramidal System 3. Viscero-Motor Involved in control of motor functions in the body (Voluntary) o Motor to the Viscera (Smooth muscles and Glands) Originate from the motor cortex a. Sympathetic – C8 to T5 to the head Pyramidal pathways - pyramidal: motor - Note: no sympathetic innervation from the o Corticospinal tract (Spinal cord-spinal nerves) Cranial Nerves ▪ Movement of muscles below the head with control b. Parasympathetic – Brainstem (CN: III, VII, IX, X) from opposite side of the brain c. 3 neuron system ▪ Direct innervation of motor neurons of spinal cord thru - Primary neuron – hypothalamus to the Anterior (ventral horn cell) viscero-motor nuclei in the brainstem o Corticobulbar/Corticonuclear tracts (Brainstem/Cranial nerve) - Secondary neuron (Preganglionic) – ▪ Movement of muscle with control from opposite side brainstem nuclei to a parasympathetic of brain ganglion ▪ Some movement of muscle in here is with control from - Tertiary neuron (Post-Ganglionic) – both cortical sides (bilateral) of the brain. Parasympathetic ganglion to effector organ ▪ Direct innervation of motor neurons of cranial nerve nuclei thru brainstem. E.g.: facial expression, turning Four Parasympathetic Nuclei in the Brainstem head side to side 1. Located inside brainstem 1. Somato-Motor 2. Edinger Westphal nucleus: Oculomotor nerve (III) Voluntary, originates from the pre-central gyrus 3. Superior Salivatory nucleus: Facial nerve (VII) Pyramidal 4. Inferior Salivatory nucleus: Glossopharyngeal nerve o 2 neuron (generally) Pathway – UMN (CNS) to LMN (PNS) (IX) o Upper Motor Neuron (UMN) - Cortex to brainstem 5. Dorsal Vagal nucleus: Vagus nerve (X) o Lower Motor Neuron (LMN) - Brainstem nuclei to Four Parasympathetic Ganglia neuromuscular junction 1. Located outside the CNS o Efferent pathway (away from the brain) 2. Ciliary Ganglion: Oculomotor nerve (III) o Decussates to the other side at the medullary pyramids 3. Pterygo-palatine Ganglion: Facial nerve (VII) o Cranial nerve decussates pyramid 4. Submandibular Ganglion: Facial nerve (VII) o Some cranial nerves have bilateral somatic motor control 5. Otic Ganglion: Glossopharyngeal nerve (IX) coming from the cortex 6. Note: Sympathetic innervation to the head – Lateral ▪ Example: CN VII, CN XI horn of the spinal cord segments C8 – T5 Page 2 of 25 [NEUROSCIENCE 1A] 1.05 CRANIAL NERVES – Dr. Crispin Allan Viado ▪ Via Superior Cervical ganglion along the internal > 5 million receptors with the ability to regenerate carotid artery The olfactory receptors and bulb are near the cribriform plate of the ▪ No sympathetic supply coming from the cranial ethmoid bone nerves Damage may lead to anosmia (Ipsilateral) 4. Viscero-Sensory Anosmia – Loss of smell Primary Sensory Ganglions: Olfactory bulb > Olfactory tract > Descending pathway to pontine reticular - Glossopharyngeal nerve ganglion (IX) receives info formation in the brainstem (Salivation – Reflex action) about blood pressure Smell and Odorants - Vagus nerve ganglion (X) receives info about heart Qualitative odor sensation: rate ✓ Example: Smell of Flower/Perfume Secondary Nuclei ✓ CN I - Solitary tract nucleus (Tractus Solitarius) Somato-sensory overtones of odorants: ▪ Assimilates the viscero-sensory information ✓ Example: Warmth, coolness, sharpness, and irritation from CN IX and X ✓ CN V (Ophthalmic and Maxillary division) ❖ Example: Someone is cooking food, you 5. Special Sensory somehow smelled it. So, you salivate, and it Smell: Olfactory nerve (I) feels like you can already taste the food just Sight/Vision: Optic nerve (II) by smelling. This explains the relation Taste: Facial nerve anterior 2/3b of the tongue (VII), between olfaction, salivation, and taste. Glossopharyngeal nerve posterior 1/3 of the tongue (IX), and Vagus nerve at back of the tongue (X) Note: Olfactory mucosa also gets branches from the Trigeminal nerve. Hearing: Vestibulocochlear nerve (VIII) - Reason why some odors have irritable character Balance: Vestibulocochlear nerve (VIII) - Explains why even when anosmic, patients can still detect certain irritating substances (for example is Table 3: Function of each Cranial Nerves ammonia) due to CN V (trigeminal nerve) CRANIAL NERVE FUNCTION SUMMARY - Nerve Function **Olfactory nerve is responsible for the smell while Trigeminal Nerve is responsible for Olfactory (I) Special sensory: Smell general sensation (pain, temperature, touch, vibration)** Optic (II) Special sensory: Vision Oculomotor (III) Somato-motor; Viscero-motor Transcribed from the video: Trochlear (IV) Somato-motor ʘ The process of olfaction or smelling begins with hair-like cilia that line the Trigeminal (V) Somato-motor Somato-sensory nasal cavity. This lining is called the olfactory epithelium. As air enters the Abducens (VI) Somato-motor nasal cavity, some chemicals in the air bind to and activate nervous system Facial (VII) Somato-motor Somato-sensory; Viscero-motor; receptors on the cilia. This stimulus sends a signal to the first order neuron Special sensory: Taste connected to the epithelial cells. The signal is carried by these neurons from Vestibulocochlear (VIII) Special sensory: Hearing-Balance the nasal cavity through the openings of the ethmoid bone and then to the Glossopharyngeal (IX) Somato-motor; Somato-sensory; Viscero-motor; olfactory bulbs of the brain. The signals then move from the olfactory bulb Viscero-sensory; Special sensory: Taste along the olfactory tracts to the olfactory area of the cerebral cortex. Vagus (X) Somato-motor; Somato-sensory; Viscero-motor; Viscero-sensory; Special sensory: Taste Accessory (XI) Somato-motor Hypoglossus (XII) Somato-motor According to Function Purely Sensory Nerves ✓ Olfactory (I) – Smell ✓ Optic (II) – Vision ✓ Vestibulocochlear (VIII) – Hearing and Balance Purely Motor Nerves ✓ Oculomotor (III) ✓ Trochlear (IV) ✓ Abducens (VI) ✓ Spinal Accessory/Accessory (XI) ✓ Hypoglossal (XII) II. Purely Sensory Nerves Cranial Nerve I: Olfactory Nerve Shortest cranial nerve Origin: Basal forebrain Sense (afferent) of smell (odors) Oldest/Most primitive sensory modality The “first” cranial nerve Derives from the embryonic nasal placode Can provoke the fastest response Figure 4: Chemosensory Parts Page 3 of 25 [NEUROSCIENCE 1A] 1.05 CRANIAL NERVES – Dr. Crispin Allan Viado o Tufted cells and granular cells - smaller nerve cells which also synapse with mitral cells o Olfactory Tract - Narrow band of white matter runs from the posterior end of the olfactory bulb beneath the inferior surface of the frontal lobe of the brain - consists of the central axons of the mitral and tufted cells of the bulb and some centrifugal fibers from the opposite olfactory bulb Note: *As the olfactory tract reaches the anterior perforated substance, it divides into medial and lateral olfactory stria o Lateral Stria - carries the axons to the olfactory area of the cerebral cortex: (primary olfactory cortex) periamygdaloid and prepiriform areas o Medial olfactory stria carries the fibers that cross the median plane in the anterior commissure to pass to the olfactory bulb of the opposite side Note: *Entorhinal area (area 28) of the Para-hippocampal gyrus, which receives numerous connections from the primary olfactory cortex, is called the secondary olfactory cortex Primary and Secondary Olfactory cortex are responsible for the appreciation of olfactory sensations Cranial Nerve II: Optic Nerve Figure 5: Purely Sensory Nerves Transcribed from the video: ʘ The process of seeing begins when light waves enter the front of the eye brightness and distinct colors are first interpreted by the structures in the back of the eye then sends a stimulus signal that the brain interprets as vision. On the exterior of the eye is an area called the cornea, it includes a pupil at which light enters the eye. Inside the eye, light is refracted by a lens and focused on a retina, a layer of receptors that lines the inside of the eye. The retina includes two types of nervous systems cells, cones that interpret the color of light waves, and rods the interpret the intensity of light. These photo receptors process information into nerve signals that travel to the optic nerve into the occipital lobes of the brain. Where signal is interpreted to represent an image. ❖ Vision – Sight Pretectal region - In conjunction with Oculomotor nerve (CN III) ✓ Light reflex ✓ Accommodation reflex Primary Neurons Figure 6: Olfaction System - Receptors in the retina ✓ Cones – Interpret color of light waves Arise from the olfactory receptor nerve cells in the olfactory mucous ✓ Rods – Interpret the intensity of light membrane located in the upper part of the nasal cavity above the level of the - Transforms light into electrical potentials superior concha o Olfactory Receptor Nerve Cells - scattered among supporting cells Secondary Neurons - consists of a small bipolar nerve cell with a coarse peripheral - Bipolar cells process that passes to the surface of the membrane and a fine - Link to optic nerve central process - Interconnect rods and cones to produce receptive fields o Olfactory Hairs - project into the mucus covering the surface of the mucous membrane - React to odors in the air and stimulate Tertiary Neurons the olfactory cells - End in lateral geniculate nucleus (LGN) of the thalamus o Olfactory Nerve Fibers - Form by the fine central process which - Some do not run into the LGN but run medial to pretectal region pass through the openings of the cribriform plate of the ethmoid ✓ Connects with the Edinger-Westphal nucleus of bone to enter the olfactory bulb - Unmyelinated and are covered oculomotor nerve (CN III) with Schwann cells ✓ Visual reflexes (example: light reflex, accommodation o Olfactory Bulb - ovoid structure which receives axons from the reflex) contralateral olfactory bulb through the olfactory tract and possesses several types of nerve cells: Optic Radiation ✓ Mitral Cell – Largest - Fibers from the lateral geniculate body to the primary visual ✓ Synaptic Glomeruli – Rounded areas formed when the cortex incoming olfactory nerve fibers synapse with the ✓ Superior parietal fibers – Responsible for the inferior dendrites of the mitral cells quadrants of the visual field Page 4 of 25 [NEUROSCIENCE 1A] 1.05 CRANIAL NERVES – Dr. Crispin Allan Viado ✓ Inferior temporal fibers – Responsible for the superior of the macula, pass posteriorly in the optic tract of the quadrants of the visual field same side - Quadratic vision 3. Optic Tract (OT) Primary Visual Cortex - Location: Emerges from the Optic Chiasma and passes - Area 17 posterolaterally around the cerebellar peduncle - Calcarine sulcus of the occipital lobe - Function: Most of the fibers terminate by synapsing with nerve - Create: cell in the LGB. Few fibers pass the Pre-Tectal Nucleus and the ✓ Images Superior Colliculus of the midbrain and are concerned with light ✓ Colors reflexes ✓ Fusion of images from both eyes o Some do not run into LGB but run medial to pretectal - Bumping the head on occipital region – cause blurring of vision – region due to location of PVC (primary visual cortex) ✓ Connects with the Edinger-Westphal - Cortical blindness – complete damage on occipital lobe nucleus of CN III ◆ Course of the Optic Nerve ✓ Visual Reflexes (e.g: light Retina (R&L) > Optic Nerve (R&L) > Optic Chiasm > Optic Tract (R&L) > Lateral reflex/accommodation reflex) Geniculate Body (R&L) > Optic Radiation (R&L) (Superior-Parietal and Inferior- ✓ PERRLA Pupil Equally Reactive to Light or Temporal) > Visual Cortex: Area 17 (R&L) Accommodation 4. Primary Visual Cortex - Optic Radiation o From lateral geniculate body to the primary visual cortex o Description: Its fibers are the axons of the nerve cells of the LGB o Function: The tract passes posteriorly through the retro lenticular part of the internal capsule and terminates in the Visual Cortex (Area 17) o Visual Cortex (Area 17) – occupies the upper and lower lips of the calcarine sulcus on the medial surface of the cerebral hemisphere o Visual Association cortex (Area 18 & 19) – Responsible for the recognition of objects and the perception of color ◆ Visual Pathway and Binocular Vision Neurons Four neurons conducting the visual impulses to Area 17 1. Rods and Cones (RnC) – Specialized receptor in the Retina 2. Bipolar Neurons – Connect the RnC to the ganglion cells 3. Ganglion Cells – its axons pass to the LGB 4. LGB nucleus – Axons passes to the Cerebral Cortex Binocular Vision o Left and right fields of vision projected on portion of both retinae. o Image in the right field: projected on the nasal half of the right retina and the left temporal half of the left retina. o In the OC, axons from the two retinal halves are Figure 7: Course of the Optic Nerve combined, forming the left optic tract. o LGB neurons complete the right field of vision on the 1. Optic Nerve visual cortex of the left hemisphere and visual field (visual - Made up of fibers from the cell axon in the ganglionic layer of the cortex of the right hemisphere). retina. It measures 3 – 4 mm at the center of its nasal side and o The lower the retinal quadrants (upper field vision) converges at the Optic Disc and exit from the eye. project on the lower wall of the Calcarine sulcus, while - Comparable to a tract w/in the CNS: the upper retinal quadrants (lower field of vision) projects o Myelinated fibers and the sheaths are formed by on the upper wall of the sulcus. oligodendrocytes sheaths o Macula Lutea is represented on the posterior part of Area o It leaves the orbital cavity through the optic canal and 17, and the periphery of the retina is represented unites with the optic nerve of the opposite side anteriorly. forming optic chiasma 2. Optic Chiasm VISIAL FIELDS - Its anterolateral angles are continuous with the optic nerves, and the posterolateral angles are continuous with the optic tracts - Location: Situated at the junction of the anterior wall and floor of the third ventricle - Decussation of fibers: o In the chiasma, the fibers from the nasal (medial) half of each retina, including the nasal half of the Macula, cross the midline and enter the Optic Tract (OT) of the opposite side. While the fibers from the temporal (lateral) half of each retina, including the temporal half Figure 8: Nomenclature of the normal visual fields Page 5 of 25 [NEUROSCIENCE 1A] 1.05 CRANIAL NERVES – Dr. Crispin Allan Viado Note: Other examples: Nasal Retinas – Temporal field of vision Temporal Retina – Nasal field of vision ❖ Optic chiasm Nasal Retinas (Temporal field of vision) ✓ Fibers cross the optic chiasm Temporal Retinas (Nasal field of vision) ✓ Fibers do not cross the optic chiasm. Remains ipsilateral ❖ Optic tract/Optic radiation/Visual cortex Will carry visual information from: ✓ Ipsilateral Temporal Retinas (Ipsilateral nasal field of vision ✓ Contralateral Nasal Retinas (Contralateral temporal field of vision ❖ Visual Field Concept Right visual field – From temporal retina of the left eye plus the nasal retina of the right eye Left visual field – From the nasal retina of the left eye plus the temporal retina of the right eye Both nasal retinas cross over to the other side at the chiasm while the temporal retinas remain ipsilateral ❖ Anopia/Anopsia - Sightlessness - The state of being blind/lack of light - Unilateral Anopia – complete blindness in one eye Figure 9: Unilateral Anopia Figure 12: Other examples of Anopia/Anopsia ❖ Hemianopia/Hemianopsia - Loss of vision in half of visual field/one side of vertical midline - Homonymous hemianopia/Hemianopsia (Optic tract/Visual tract) o Example: Left Homonymous Hemianopia Figure 10: Left Homonymous Hemianopia ❖ Quadrant anopsia/Quadrantanopia - Optic radiation damage (Parietal/Temporal) - Loss of a quarter of the field of vision o Example: Right Superior Homonymous Quadrantanopia Figure 11: Right Superior Homonymous Quadrantanopia Figure 13: Other examples of Anopia/Anopsia Page 6 of 25 [NEUROSCIENCE 1A] 1.05 CRANIAL NERVES – Dr. Crispin Allan Viado Application: ◆ General Characteristics of the Cochlear Nerve Cutting the right retinal nerves (both nasal and temporal retinas) – Result to The cochlear part has both ventral and dorsal nucleus. Once the complete loss of vision on the right eye nerve arrives in the pons they will now synapse with the nucleus. Cutting the right temporal retina – Result to loss of vision on the nasal side of The ventral and dorsal nucleus connect with the olivary nucleus the right eye called “left hemianopia” of the right eye found in the pons wherein there is comparison of left\right ear. That information will go to the inferior colliculus where Cranial Nerve VIII: Vestibulocochlear Nerve integration with proprioceptive information coming from the Maintains balance and hearing body. Purely sensory nerve From the inferior colliculus it goes to the thalamus and move to Transmits sound and equilibrium (balance) information from the inner ear the auditory cortex particularly to temporal gyrus where analysis to the brain of the sound occurs. Nuclei in the pontomedullary junction consist mostly of bipolar neurons. Two functional divisions: ◆ Cochlear Part of CN III (Hearing) 1. Vestibular nerve (Equilibrium/Balance) - The cochlear nerve travels away from the clay of the inner ear - Lesion will cause: Disequilibrium, vertigo, nystagmus which starts at spiral ganglia 2. Cochlear nerve (Hearing) Spiral Ganglia – Nuclei consist mostly of bipolar - Destructive lesion will cause: Hearing loss/sensorineural deafness neuron - Irritative lesion will cause: Tinnitus Sensory Organ – Organ of Corti (primary neuron) ✓ Inner hair cells ✓ Primary neuron ✓ Housed in the spiral ganglion Detects sound waves that vibrate the eardrums Secondary Neuron ✓ Superior olivary nucleus Information from both ears is compared to localize the sound source Third Neuron ✓ Medial geniculate body (thalamus) Temporal Gyrus ✓ Low frequency – Anterolateral cortex ✓ High frequency – Posteromedial cortex Figure 14: Structure of the Inner Ear ❖ Anatomy: ʘ Emerges from pontomedullary junction at the cerebellopontine angle ʘ Exits via the Internal acoustic meatus (with CN VII) - Damage of the internal acoustic meatus due to fracture or tumor – manifestation on damage of cranial nerve VII (facial) and VIII (abducens) – problem with facial expression and loss of hearing ʘ Vestibular apparatus and semicircular canals - Afferent messages associated with sense of equilibrium/ balance - Vestibular radix - composed of semicircular canals ʘ Cochlea - Afferent impulses associate with hearing Figure 16. Parts of the Middle and Inner Ear - Cochlear radix - shell shaped ʘ Cochlear part from cochlear ganglion and vestibular part from vestibular ❖ Analysis of Sound ganglia, they will form a single nerve called vestibulocochlear nerve and exit Associative Auditory Cortex to the cerebellopontine angle and reach brainstem (pons) o Comparison with former experiences of sound is done Integration o Speech – Let Hemisphere (temporal lobe) – Wernicke’s and Broca’s areas o Music – Right Temporal Lobe Figure 15: Vestibulocochlear Pathway Page 7 of 25 [NEUROSCIENCE 1A] 1.05 CRANIAL NERVES – Dr. Crispin Allan Viado - Hearing loss (Sensorineural) - Vertigo - False sense of motion - Loss of equilibrium (especially in dark places) - Motion sickness - Nystagmus – Irregular movement of eyes; usually happens when travelling (eye wanders around the surrounding) - Gaze-evoked tinnitus III. Purely Motor Cranial Nerves Figure 17: Analysis of Sound Five purely motor nerves ◆ Vestibular Part of CN VIII (Balance) 1. Oculomotor (CN III) Vestibular Ganglia - Main function is moving the eyeball in all directions - Nuclei: Cell bodies of bipolar neurons - Adduction (inward movement of the eye) is the most important Five Sensory Organs: action. - 3 cristae (semicircular canals) – Afferent receptor in response to - Elevates eyelid (levator palpebrae superioris) rotational acceleration - Constrict pupils (papillary constrictor – short ciliary nerve branch) - Otolith Organs: - Accommodates the eye (by contracting the ciliary muscle – short ✓ Maculae of Saccule – Vertical Acceleration ciliary nerve branch) ✓ Maculae of the Utricle – Linear/Horizontal Acceleration 2. Trochlear (CN IV) - Motor to the superior oblique muscles 3. Abducens (CN VI) - Motor to lateral rectus muscle (all the muscles here are extra ocular muscles) - Abducts eye (outwards) 4. Accessory (CN XI) - Motor to sternocleidomastoid and trapezius 5. Hypoglossal (CN XII) - Motor to muscles of the tongue *Oculomotor, trochlear, and abducens nerves will supply the extraocular muscles A. CN III: Oculomotor Nerve - Responsible for lifting the upper eyelid; turning the eye upward, downward, and medially; constricting the pupil; and accommodating the eye - Originates at the mesencephalon or the midbrain - Has two nuclei – nucleus oculomotorius (motor), Edinger Westphal (parasympathetic) (*nuclei – nerve cell bodies located in the midbrain) Figure 18: Balance (Vestibular part) *Note: Vestibule-Ocular reflex is also known as Doll’s eye movement Figure 19. Pathway of Oculomotor Nerve ʘ Cranial Nerve VIII: Symptoms of Damage (*Patient with otitis media will experience all these symptoms) Page 8 of 25 [NEUROSCIENCE 1A] 1.05 CRANIAL NERVES – Dr. Crispin Allan Viado - It supplies the muscles of the eye by entering the superior orbital ❖ Causes deficits in ipsilateral eye, difficulty in fissure moving eye medially and vertically - Most of the fibers in cranial nerve III enter the supplementary ❖ Diplopia or double vision (common) orbital fissure and supplies the superior rectus muscle (moves eye ❖ Drooping of the eyelid may occur due to upwards), inferior rectus muscle (moves eye downwards), medial paralysis of the levator – palpabrae rectus muscle (moves eye towards the nose), inferior oblique superioris muscle (moves eye up and out), levator palpebrae (moves eyelid) ❖ The pupillary constriction muscle is - Some fibers will go to the ciliary ganglion that is responsible for impaired the pupil on the side of damage the contraction of ciliary muscle & papillary contractor muscle. may remain dilated a condition known as These are parasympathetic functions of oculomotor nerve. mydriasis. - The oculomotor nerve runs in the lateral wall also of the calculus sinus together with the cellular nerves Parasympathetic fibers (Visceromotor function) ✓ Some of the fibers in the cranial nerve perform parasympathetic function that is the visceral motor function ✓ Ciliary ganglion – short sensory nerve: sensory muscle ✓ This is through the ciliary ganglion which gives rise to short ciliary nerve that supplies ciliary muscle, which makes the lens rounder. So, it varies the shape of lens. ✓ Accommodation (In order that you must focus on something, that is the ciliary muscle will contract to make your lens focus on that near object that is getting near you) ✓ Constricts pupil (pupillary sphincter) Figure 20. Oculomotor Nerve and Superior Orbital Fissure ❖ Decreases the diameter of the pupil ❖ Pupillary constriction (meiosis) - It exits through the superior orbital fissure before it enters the orbit - REMEMBER: all the nerves that innervate the eye, the extraocular muscles will enter the superior orbital fissure (foramina) Somatic Motor Neurons ✓ It innervates the extra ocular muscles ✓ Via oculomotor neurons Preganglionic Parasympathetic Neurons ✓ CN III (Oculomotor), VII (Facial), IX (Glossopharyngeal), X (Vagus) – Has parasympathetic functions ✓ Papillary constriction and accommodation ✓ Via Edinger-Westphal nucleus (accessory oculomotor nucleus) Figure 22: Ciliary Ganglion ✓ Superior cranial nerve III fibers – innervates the extra ocular muscle Ciliary Muscle ✓ Lens accommodation – varies the lens shape Figure 21: Muscles that help in the movement of the eye ✓ All the extraocular muscles are innervated by the Figure 23: Ciliary Muscle oculomotor nerve except the superior oblique which is innervated by cranial nerve IV or trochlear nerve Pupillary sphincter/Constrictor pupillae and the lateral rectus which is innervated by cranial ✓ Pupillary constriction nerve VI or abducens nerve ✓ Oculomotor nerve damage: Page 9 of 25 [NEUROSCIENCE 1A] 1.05 CRANIAL NERVES – Dr. Crispin Allan Viado ✓ Constrict the pupil to decrease the size of the pupils, it Summary: Shine a light → Optic nerve (afferent component) goes on both sides → is called as meiosis Received on both sides of the Edinger Westphal nucleus → CN III and travel on both eyes *Both the actions, contraction in ciliary muscle as well as the constriction of pupils → Ciliary ganglion → Short ciliary nerve → Pupillary constrictor muscles—constrict the contribute to the regulation of eyeball pressure (measured by tonometer, used by pupils on both on both eyes right and left ophthalmologist)* Accommodation Reflex Reflex exam - The “near response” of the eye ✓ When doing examination, most of the times the cranial nerve III involves the cranial nerve II because they both have a relationship in terms of the reflex examination particularly pupillary like reflex and the accommodation reflex ✓ Pupillary light reaction - direct and consensual ❖ Consensual light reflex - If you shine a light on one eye that will result in constriction of pupil not only on the lighted eye but also on the other eye ❖ Direct light reflex - If you shine a light only on the right eye, the left eye will also constrict Accommodation ✓ The afferent component of the pupillary reflex is the optic nerve cranial nerve III ✓ The efferent component to the parasympathetic component of the cranial nerve III on both sides Figure 26: Longitudinal section of the eye (bilaterally) - Reflex action of the eye in response to focusing on near object, then looking at distant objects - Coordinated changes in: a. Convergence – both eyes will converge to focus on the object b. Lens shape – changes in shape of lens c. Pupillary size – changes in pupillary size (pupillary constriction) - Controlled by the parasympathetic nervous system (via Edinger-Westphal nucleus) - If we draw an object near our eyes, both eyes will converge through the left and right medial rectus Figure 24: Pupillary Light Reflex 1. If you shine a light on one eye 2. The conduction of impulses will travel to the optic nerve, which has two fibers: temporal fibers and nasal fibers 3. Nasal fibers will cross over at the optic chiasm so both conduction will proceed towards the pretectal nuclei at the back. 4. Pretectal nucleus of the body (pre-tectum and tectum at the midbrain at the superior colliculus). pretectal nuclei on both sides will have the Edinger Westphal nucleus that is also located in the mid brain 5. From the Edinger Westphal nucleus it will send that information towards the oculomotor nerves 6. Via the oculomotor nerves it will travel through the towards the ciliary ganglia Figure 27: Convergence eye Test on both sides and goes towards the ciliary nerve to innervate your pupillary constrictor muscle to affect an action ❖ Convergence of the two eyes – this is to make sure the object is focused on 7. There will be constriction of the pupils on both eyes that is known as concept the fovea of each retina. Failure of doing so – for example, when the eye direct reflex and a consensual reflex on the other eye muscles are weak – would result in double vision. This is because the object is focused on different parts of the two retinas and the brain sees two images. ❖ Constriction of pupil – this is to reduce spherical aberration. Spherical aberration occurs when light rays hit the edge of a lens and produce blurriness. Constricted pupil allows light rays to enter the lens only at the center where they are best refracted. ❖ Accommodation of the lens – ciliary muscles contract to make the shape of the lens more convex. This increases the optical power of the lens. It now can converge the divergent light rays onto the retina. ❖ Presbyopia − is a very common age-associated condition in which the eye loses the ability to adjust to near vision. In presbyopia, the lens loses its flexibility with age and becomes stiff. It can no longer change its shape to accommodate near vision. Figure 25: Pathway of the Pupillary Light Reflex Page 10 of 25 [NEUROSCIENCE 1A] 1.05 CRANIAL NERVES – Dr. Crispin Allan Viado ✓ Corrected with convex lenses that converge the light rays slightly - Aids more in abduction before they enter the eye. Presbyopia is not to be confused with - Follows the same course as the CN III hyperopia, a condition in which the eyeball is too short. - Nucleus ▪ Found in the anterior part of the gray ◆ CN III: Looking up and elevating the eyelids by levator palpebrae superioris matter that surrounds the cerebral aqueduct of the midbrain Remember: Three reactions in accommodation reflex ▪ Lies inferior to the oculomotor nucleus at the level of inferior colliculus 1. Convergence through the contraction of the medial rectus ▪ After leaving the nucleus, the nerve fibers pass posteriorly around the central gray 2. Change in the shape of your lens through the contraction of your ciliary matter to reach the posterior surface of the muscle midbrain ▪ Receives corticonuclear fibers from both 3. Pupillary constriction through the contraction of your pupillary cerebral hemispheres sphincter (Mydriasis – opposite of miosis; instead of constricting upon ▪ Receives the tectobulbar fibers, which shining the pupil it will dilate). connect it to the visual cortex through the superior colliculus ▪ Also receives fibers from the medical longitudinal fasciculus by which it is connected to the nuclei of the third, sixth, and eighth cranial nerve - Most slender of all cranial nerves - The only cranial nerve to leave the posterior surface of the brainstem, emerges from the midbrain and immediately decussates with the nerve of the opposite side - Passes forward through the middle cranial fossa in the lateral wall of the cavernous sinus and enters the orbit through the orbital fissure Figure 28: Muscles controlling the eyelid C. CN VI: Abducens Nerve - Draw the eye toward the side of the head o When you look up, why the upper eyelid also retracts upward? the reason is - It is a motor nerve, supplies the lateral rectus muscle (turning the because the levator palpebrae superioris which is innervated by CN III and eye laterally) the superior rectus and the inferior oblique which elevates your eyeball is - Enter the orbit through superior orbital fissure also innervated by CN III. - Innervates the Lateral Rectus muscle - Abducts the eye o It continues from the lesser wing of the sphenoid, just above the optic floor - Abducens nucleus is in the pons. The small motor nucleus is and it proceeds to become the aponeurosis and this portion inserts the skin situated beneath the floor of the upper part of the fourth the upper eyelid as well as a superior tarsal plate. it is a skeletal muscle i.e., ventricle, close to the midline and beneath the colliculus facialis. if you are looking up and the eyelid retracts upwards it is a voluntary action, - The nucleus receives afferent corticonuclear fibers from both not involuntary because we are controlling it voluntarily. cerebral hemispheres. It receives the tectobulbar tract from the superior colliculus, by which the visual cortex is connected to the nucleus. It also receives fibers from the medial longitudinal fasciculus, by which it is connected to the nuclei of the third, fourth, and eighth cranial nerves - Course of the Abducent Nerve: The fibers of the abducent nerve pass anteriorly through the pons and emerge in the groove between the lower border of the pons and the medulla oblongata. It passes forward through the cavernous sinus, lying below and lateral to the internal carotid artery. Extraocular Muscle Movements CN III: Oculomotor o Superior (Up), Inferior (Down) and Medial (In- adduction) rectus Figure 29: Ptosis defect of CN III o Inferior oblique – Up and in (upward adduction) Damage to CN III – Ptosis o Ciliary muscle (Accommodation) o Levator Palpebrae Superioris (eyelid B. CN IV: Trochlear Nerve elevation) - Innervates the superior oblique muscle - Moves eye inferiorly when adducted CN IV: Trochlear - Internally rotates when abducted Page 11 of 25 [NEUROSCIENCE 1A] 1.05 CRANIAL NERVES – Dr. Crispin Allan Viado o Superior oblique o Down and out (downward abduction) CN VI: Abducens o Lateral rectus Figure 32: Conjugate Eye Movement Figure 30: Six Cardinal Position of Gaze Figure 33: Clinical presentation: Mass effect on Cavernous Sinus ʘ Cavernous Sinus - CN (III, IV, V1, V2, VI): Ptosis, diplopia, “Frozen eye”, Ophthalmoplegia, facial pain - Occlusion of C5 (venous outflow blockage): Proptosis (exophthalmus), chemosis - Carotid artery encasement: Stroke **Q: What is the first nerve that will be affected if there is sudden development of aneurysm? A: Abducens** ❖ Types of Conjugate Eye Movements; Site of Control ✓ Saccadic (command): rapid movement from one fixation to another; Frontal lobe. ✓ Pursuit: the slow eye movement used to maintain fixation to a moving object; Occipital lobe ✓ Vestibulo-positional (Vestibulo-ocular reflex): eye movement that compensates for movement of the head to maintain fixation (Doll’s eye - SIGN THAT YOU’RE STILL ALIVE); Cerebellar Vestibular nuclei ✓ Convergence: the movement that maintain fixation as an object is Figure 31: Cranial Nerve Nuclei in Brainstem brought close the face; Midbrain ◆ Conjugate Eye Movement Table 4: Eye Movements and their Site of Control Motor coordination of the eyes that allows for bilateral fixation on a single object. Movement of both eyes to maintain binocular gaze “Yoked” eye movement Page 12 of 25 [NEUROSCIENCE 1A] 1.05 CRANIAL NERVES – Dr. Crispin Allan Viado D. CN XI: Accessory Nerve - Arises from medulla - Leaves the skull through the jugular foramen - Contributions from spinal radices C1-C6 entering the skull in the foramen magnum - It has a nucleus known as nucleus ambiguous - The nucleus receives corticonuclear fibers from both cerebral hemispheres - The efferent fibers of the nucleus emerge from the anterior surface of the medulla oblongata - between the olive and the inferior cerebellar peduncle. - The nerve runs laterally in the posterior cranial fossa and joins the spinal root. The two roots unite and leave the skull through the jugular foramen. - The nerve fibers emerge from the spinal cord midway between Figure 35: Sternocleidomastoid the anterior and posterior nerve roots of the cervical spinal nerves. The fibers form a nerve trunk that ascends into the skull Tilt, flexion and rotate the head through the foramen magnum. ✓ Flexion – contract both Sternocleidomastoid - The only cranial nerve to both enters and exits the skull ✓ Tilt – Tilting the head will contract the ipsilateral - Purely motor: Sternocleidomastoid and Trapezius muscles sternocleidomastoid o Example: Right head tilt will contract right sternocleidomastoid Rotate/Turn side to side – Contraction turns the head to opposite side turning o Example: Rotating/Turning towards left will contract the right sternocleidomastoid. Figure 34: Function Summary of the Abducens Nerve - Nucleus is innervated from cortex to the contralateral side (Decussation at the medullary pyramids) - Bilateral sternocleidomastoid muscle control from cortex - Somato-motor to the: ▪ Sternocleidomastoid ▪ Trapezius muscle - Sternocleidomastoid ▪ Tilt, flexion and rotate the head ▪ Contraction turns the head to opposite side - Trapezius ▪ Shrug the shoulder ▪ Ipsilateral contraction - Note: Ipsilateral cerebral cortex (UMN) supplies the contralateral trapezius and sternocleidomastoid plus ipsilateral Figure 36: Trapezius sternocleidomastoid muscle thus a single UMN lesion can give rise to signs of both sides. But the dominant cortex will still be the Shrug the shoulder contralateral cortex Ipsilateral contraction - The right cerebral cortex will still be dominant control for the Left sternocleidomastoid and trapezius muscle and vice versa, thus the dominant weakness will still be on the contralateral side. ◆ CN XI Damage Damage to the right motor cortex - An acute damage to the UMN (Corticobulbar tract) will cause predominantly contralateral hemiplegia/paresis of sternocleidomastoid and trapezius - Note: Contraction of sternocleidomastoid will turn/rotate the head to the opposite side, tilt head to the ipsilateral side. - Weak Left Sternocleidomastoid and Trapezius Page 13 of 25 [NEUROSCIENCE 1A] 1.05 CRANIAL NERVES – Dr. Crispin Allan Viado ✓ Head tilted towards right/side of UMN lesion (Strong - Hypoglossal nucleus is situated close to the midline immediately side, which is the right sternocleidomastoid will beneath the floor of the lower part of the fourth ventricle dominate – supplied by the intact left motor cortex) ✓ Weak shrug on the left side (Contralateral cortical ◆ The Tongue innervation of trapezius) Primary organ of taste Damage to the right accessory nerve (peripheral nerve)/LMN Manipulate food for mastication - Weak/paralysis turning/rotating head to left side (contraction of Phonetic articulation sternocleidomastoid turns head to the opposite side) Natural “toothbrush” - Head tilted towards left (opposite intact accessory nerve will 2 groups of muscle (Intrinsic and Extrinsic) dominate, cannot tilt head towards right side of LMN lesion) - Weak/paralysis of shoulder shrug right (trapezius: ipsilateral) ** Q1: Head tilted towards left, plus weak shoulder shrug right, eye deviated towards left. Where is the lesion? A: Left UMN/Central Left Cortical/Left Corticobulbar damage** ** Q2: Atrophy of right trapezius and sternocleidomastoid and unable to shrug right shoulder, unable to rotate head towards the left side, head tilted slightly towards left. Where is the lesion? A: Right LMN/Accessory nerve damage** Figure 39: Intrinsic Muscles of the Tongue Figure 37: Hemiplegia/paresis E. CN XII: Hypoglossal Nerve Brainstem > Hypoglossal nucleus > Hypoglossal canal > Intrinsic and Extrinsic tongue muscles Figure 40: Extrinsic Muscle of the Tongue The extrinsic muscles originate from bone and extend to the tongue. Their main function is altering the tongue’s position allowing for protrusion, retraction, and side to side movement Innervated by the Hypoglossal Nerve (XII) Genioglossus: arises from the mandible and protrudes the tongue, it is also known as the “safety muscle” of the tongue since it is the only muscle having the forward action Hyoglossus: arises from the hyoid bone and depresses the tongue Styloglossus: arises from the styloid process of the temporal bone and elevates and retracts the tongue Innervated by the Vagus Nerve (X) Palatoglossus: arises from the palatine aponeurosis, and Figure 38: Hypoglossal Nerve depresses the soft palate, moves the palatoglossal fold towards the midline, and elevates the back of the tongue **Note: Palatoglossus is not innervated by CN XII but rather by CN X** ❖ Tongue Innervation - Purely motor: intrinsic/extrinsic muscles of the tongue ✓ Motor Innervation: - Supplies all the intrinsic muscles of the tongue as well as the - CN XII – Intrinsic and Extrinsic Muscles styloglossus, hyoglossus and the genioglossus - CN X – Palatoglossus - The nerve is invo