Origins of Cranial Nerves PDF

Telencephalon: our well-developed brain Diencephalon: also part of our brain, anatomically inferior - Both of these are the precursors of prosencephalon Prosencephalon Referred to as the forebrain Most anterior part of the developing brain Divides into telencephalon and diencephalon...

Telencephalon: our well-developed brain Diencephalon: also part of our brain, anatomically inferior - Both of these are the precursors of prosencephalon Prosencephalon Referred to as the forebrain Most anterior part of the developing brain Divides into telencephalon and diencephalon during embryonic development Telencephalon ○ Responsible for higher brain functions such as cognition, emotion, voluntary movement, and sensory processing Diencephalon ○ Thalamus, hypothalamus, epithalamus, and subthalamus ○ Relay station and combinations of motor control; regulates sensory processes ○ Regulates autonomic functions and sleep cycles Cerebral Hemispheres: involved in cognitive, sensory, and motor functions Cortex: Outer layer of the cerebral hemispheres Responsible for higher brain functions: thought, reasoning, perception, and voluntary movement Frontal, parietal, occipital, and temporal lobes Basal ganglia Caudate nucleus, putamen, and globus pallidus Involved in the regulation of movement and coordination Limbic system Hippocampus and amygdala Emotion, memory, and learning Olfactory bulb (CN I) Involved in the sense of smell Directly connected to the telencephalon Diencephalon: Thalamus: relay station for sensory and motor signals Hypothalamus ○ Regulates autonomic/involuntary functions ○ Body temperature, hunger, thirst, sleep-wake cycles, and controls the endocrine system Epithalamus ○ Includes the pineal gland ○ Secretes melatonin and helps regulate sleep patterns Midbrain: Above the pons  Involved in functions such as vision, hearing, motor control, sleep/wake regulation, arousal, and temperature Corpora quadrigemina (which includes the superior and inferior colliculi) ○ Superior colliculi: damage here will result in visual problems ○ Inferior colliculi: processing of hearing information Substantia nigra (substance that is created here for the production of dopamine to regulate movement- Parkinson’s disease) - involved in movement coordination CNN Pons: (waterboy) Between the midbrain and the medulla oblongata ○ Intermediate structure that serves as a director in where directing where certain things go Serves as a bridge for communication between different parts of the brain - cerebellum and the cerebrum Breathing, sleep, and posture CNN: CN V up to vestibulococlear nerve (CN 8) Medulla oblongata: Base of the brainstem Connects to the spinal cord Controls autonomic functions – HR, BP, breathing, swallowing, vomiting Centers to maintain homeostasis CNN: Olfactory nerve: (CN I)- Afferent stimulus** sensory** Originates from the olfactory bulbs (inferior surface of the frontal lobe of the brain Olfactory nerve fibers extend from the olfactory bulbs Receives sensory input from the olfactory receptors located in the nasal cavity Receptors are in the olfactory epithelium specialized tissue in the upper part of the nasal cavity Olfactory sensory neurons in the nasal epithelium detect odor molecules and generate nerve impulses (cribriform plate) Olfactory Bulbs– synapses occur Olfactory Tracts– information is sent through the olfactory tracts to various brain regions, including the olfactory cortex, where odor perception and processing occur Projection ○ Olfactory cortex (located in the temporal lobe) – critical for the conscious perception of smell. ○ Amygdala – involved in emotion and memory, linking smells with emotional responses and memories. ○ Hippocampus –plays a role in forming memories related to scents Also contributes to the perception of taste – loss of the sense of smell can significantly affect the perception of taste Optic nerve (CN II)  Develops from an outpouching from the diencephalon Originates from the retina of each eye*; ON head is our nucleus of CN II**** ○ Composed of ganglion cell layer (#8 of 10 layers) Arise from the ganglion cells in the retina RPE (light-sensitive layer) by way of hyperpolarization converts light into neural signals Optic nerve fibers arise from the ganglion cells in the retina– receive signal for more outer layers Pathway ○ RPE hyperpolarization– phototransduction process in the retina ○ Retinal Ganglion Cells– receive visual signal from photoreceptors and the other more outer layers ○ Optic Nerve– axons of the retinal ganglion cells bundle together to form the optic nerve, which exits the eye through the optic disc ○ Optic Chiasm– nasal fibers cross ○ Optic Tracts– project to the lateral geniculate nucleus (LGN) in the thalamus ( which is the primary relay station for visual information) ○ Optic radiations – transmit visual information from the lateral geniculate nucleus (LGN) of the thalamus to the primary visual cortex in the occipital lobe Functions ○ Recognition of shapes, colors, and movement ○ Depth perception and three-dimensional vision ○ Contrast and brightness differentiation CN III to XII: Originate from the brain stem Are embryologically homologous with spinal nerves Nuclei of them derived originally from cell columns homologous with the columns of the spinal cord CN III (Oculomotor): Nucleus located in the midbrain, at the level of the superior colliculus Control EOMS Parasympathetic functions through EW nucleus (accessory) Oculomotor nucleus - at the level of the superior colliculus ○ Fibers of oculomotor nucleus exits BS through the cerebral peduncles and via interpeduncular fossa ○ Passes between the posterior cerebral and superior cerebellar arteries before entering the orbit through SOF ○ Once in the orbit, the oculomotor nerve branches into: Superior division: LR, SR Inferior division: MR, IO, IR - voluntary Additionally, it carries parasympathetic fibers to the ciliary ganglion for controlling pupil constriction and lens accommodation Motor functions  ○ Elevation, depression, adduction, and lateral rotation Parasympathetic function ○ Pupi constriction ○ Accommodation Clinical correlations ○ CN III palsy with or w/o pupil sparing W/ pupil sparing: most likely due to ischemia (ex: diabetic is uncontrolled and sees double; ptosis; eye is deviated down and outward; gets an ischemic neuropathy response to CN III and can get a full-blown ON palsy that is irreversible) W/o pupil sparing: aneurysm in post. cerebral artery ○ INO (internuclear ophthalmoplegia) An ocular movement disorder caused by a lesion of the medial longitudinal fasciculus CN 3 & 6 have to connect by MLF (medial longitudinal fasciculus); when we have problems with this connection, the eye will not be able to do conjugate movements so in INO = it is an impaired adduction of the ipsilateral (eye that goes towards nose will not move) eye with nystagmus of the abducting eye Left INO: left eye unable to adduct in lateral gaze CN IV (Trochlear): Nucleus located at the midbrain and fibers emerge from the dorsal aspect of the brainstem (unique) Is the only one that goes dorsally and has one activity: activity on the superior oblique muscle Level of the inferior colliculus Emerges from the dorsal surface of the brainstem Passes laterally around the midbrain and exits at the level of the superior colliculus Enters the orbit through the SOF Innervates SOM tilting the eye downward and laterally  Superior oblique: Z-axis = intorts, depresses, and minimal abduction ○ Vs. inferior oblique: extorts Motor function: depression, abduction (minimal), and intorsion (rotating the top of the eye toward the nose) Clinical ○ Superior Oblique Myokymia Brief episodes of involuntary vertical and torsional movement: twists or rotations of the eye Irritation or Damage: This can occur due to compression of the trochlear nerve, which innervates the superior oblique muscle ○ SOM palsy Trauma Vascular issues: diabetic neuropathy, ischemia Mass effect: midbrain tumors Systemic conditions: MS ○ Decompensated fovea CN V (Trigeminal): Trigeminal motor nucleus ○ Located in the pons, this nucleus ○ Contains the cell bodies of motor neurons that supply the muscles involved in mastication (chewing) Sensory ganglia ○ Trigeminal ganglion (Gasserian- NOT at the brainstem) at the trigeminal cave of temporal cranial fossa ○ 3 nuclei (mesencephalic [most superior], principal sensory, and spinal trigeminal) located in the pons and part of the medulla oblongata Mixed nerve: somatomotor and somatosensory fibers Somatomotory fibers: muscles of mastication Somatosensory fibers: entire face, from the lower margin of the mandible to the top of the scalp Trigeminal (Gasserian) ganglion ○ I plays an essential l role in the sensory and motor functions of the face ○ Located in a cavity called Meckel's cave at cranial fossa, near the temporal bone/ lateral to the cavernous sinus ○ Composed of the cell bodies of sensory neurons (divisions) Ophthalmic nerve (V1)– sensory innervation to the forehead, upper eyelid, and cornea. Maxillary nerve (V2)– supplies the mid-face, including the cheeks, upper lip, and part of the nasal cavity Mandibular nerve (V3)– lower lip, chin, and parts of the ear, also has a motor component that innervates muscles of mastication ○ Functions:  The Gasserian ganglion is primarily responsible for the transmission of sensory information from the face to the brain, including touch, pain, temperature, and proprioception Mastication: motor movement in association with sensory output from mandibular nerve gives sense of orientation while chewing Sensory nucleus ○ Spinal trigeminal nucleus Extends from lower pons to upper cervical spinal cord (C1-C3) Process pain and temperature sensations from the face Primary sensory fibers synapse and secondary direct to the thalamus ○ Mesencephalic nucleus Located in the midbrain Contains the cell bodies of primary sensory neurons that provide proprioceptive information from the muscles of mastication and the temporomandibular joint (TMJ) Proprioceptive fibers from the muscles of mastication synapse and relay to the trigeminal motor nucleus– allowing for coordination in mastication ○ Principal sensory nucleus In the pons Processes light touch and proprioceptive sensations from the face Primary fibers enter the pons and synapse and secondary neurons then project to the thalamus (VPM) VPM: Ventral posteromedial nucleus of the thalamus ○ Mainly responsible for sensation in the face ○ Process sensory information from the face: pain, temperature, touch CN VI (Abducens): Nucleus in the pons, near/anterior to the fourth ventricle (aqueduct of Sylvius; CSF traveling through and it is coming from 3 to 4) ○ Lateral, 3rd, and 4th ventricles (4th is anterior and from there goes to the subarachnoid space for fluid to leave to the spinal cord) Works along with w/ CN 3: conjugate lateral movements ○ Nothing but lateral vergences (the H across) Abducens nucleus, located in the pons and fibers emerge at the junction of the pons and the medulla oblongata and travels anteriorly towards the orbit (SOF) ○ Travel inferiorly to emerge then travel anteriorly and pass cavernous sinus and project more anteriorly to superior orbital fissure Innervates LR, responsible for eye abduction Involved in lateral duction and conjugate vergence Clinical ○ Isolated Abducens Nerve Palsy: Uncrossed diplopia (esotropia) and lack of abduction Causes  Increased intracranial pressure (tumor, IIH, or intracranial hemorrhage) Which nerve gets the most affected in idiopathic cranial hypertension? ○ 6th cranial nerve palsy may be present as a non-localizing sign of increased intracranial pressure Trauma to the base of the skull Ischemic insult Demyelinating disease (multiple sclerosis) ○ INO What is the difference between left INO versus right INO? 3& 6: Motor nerves (IN out- coming from the brain– frontal lobe, which part of the frontal lobe- Right) Frontal Eye field that is affected (in this case the RFEF), patient will be unable to gaze towards the left {lesion is in the RFEF domains the conjugate eye movement towards the left} Frontal Eye Field and paramedian pontine reticular formation (PPRF) CN VII (Facial): Its motor nucleus in the pons, along with sensory nuclei (nucleus of the solitary tract for taste) extending to the medulla Originates at the pons, travels through the internal acoustic meatus and emerging at the stylomastoid foramen Responsible for controlling the muscles of facial expression Transmits taste sensations from the anterior two-thirds of the tongue Motor Function ○ Muscles of facial expression – smiling, smiling, frowning, and closing the eyes Sensory Functions ○ Carries taste sensations from the front 2/3 of the tongue Parasympathetic Functions ○ Submandibular and sublingual salivary glands ○ Lacrimal gland Motor Nucleus: controls the muscles of facial expression ○ IN OUT RESPONSE, from there it relays facial expression  Sensory Nucleus: involved in taste sensations, it is part of the rostral nucleus solitarius and processes information from the anterior two-thirds of the tongue Parasympathetic Nuclei: these include the superior salivatory nucleus, which is responsible for the parasympathetic innervation of the lacrimal gland (V/1, hitchhiker) and salivary glands Temporal Branch: muscles of facial expression in the forehead and above the eyes Zygomatic Branch: muscles that control the upper cheeks Buccal Branch: muscles of the cheeks and upper lip Marginal Mandibular Branch: muscles of the lower lip and chin Cervical Branch: platysma muscle in the neck Chorda Tympani: carries taste sensations from the anterior two-thirds of the tongue and parasympathetic fibers to the submandibular and sublingual salivary glands Greater Petrosal Nerve: provides parasympathetic innervation to the lacrimal gland and nasal mucosa Common Conditions ○ Bell's Palsy – sudden, temporary weakness or paralysis of the muscles on one side of the face CN VIII (Vestibulocochlear nerve): Arises from 2 nuclei located in the pons and medulla oblongata ○ Cochlear nucleus (for hearing) ○ Vestibular nucleus (for balance) Nuclei originate at the junction of the pons and medulla oblongata Cochlear Nuclei: process auditory information from the cochlear branch Vestibular Nuclei: process balance and spatial orientation information from the vestibular branch Fibers emerge and travel internal acoustic meatus (temporal bone), traveling with CN 7 in the meatus With the internal meatus the nerve branches out into the cochlear branch and the vestibular branch Cochlear branch enters the cochlea – and transmits sound information Vestibular branch connects with semicircular canals for balance Functions ○ Hearing TM –pick up sound vibration Ossicles – malleus (hammer) attached TM connects to the incus (anvil), and in turn connects to the stapes (stirrup) to amplify vibration signal Organ of Corti – hair cells bending causes transduction ○ Cochlear branch – transmit neural signals to the auditory cortex of the brain via cochlear nucleus Balance ○ Movement and position signal are detect in the semicircular canals and otolith – endolymph and utricles/saccules ○ Ampulla hair cells are activated cause transduction  ○ Vestibular branch – transmits neural balance and equilibrium signals to areas of the brain that control balance and coordination via the vestibular nucleus Assessment ○ Auditory Brainstem Response (ABR) measure brain’s electrical activity in response to sound ○ The Dix-Hallpike maneuver – calcium crystals displacement Clinical ○ Hearing Loss – neurosensorial (acoustic neuroma) and conductive (barotrauma) ○ Vestibular Disorders – BPPV, Meniere's disease CN IX (Glossopharyngeal nerve): Originates from several nuclei in the medulla oblongata ○ Nucleus ambiguous (motor) ○ Solitary nucleus (sensory for taste and visceral sensation) Mixed nerve: somatosensory, somatomotor, viscerosensory and visceromotor fibers ○ Somatosensory: general (pain) from tongue (post 1/3) pharynx ○ Somatomotor: muscles of the pharynx ○ Viscerosensory: taste (post. 1/3 of the tongue) swallowing reflex, carotid sinus ○ Visceromotor: parotid parasympathetic innervation (with V/3) Branches: Pharyngeal – contributes to the pharyngeal plexus and provides motor innervation to the stylopharyngeus muscle (swallowing) Tonsillar – sensory innervation to the palatine tonsil (sensation of touch and pain) Lingual – carries sensory fibers for taste and general sensation from the posterior one-third of the tongue – perception of taste as well as touch, temperature, and pain Carotid sinus - innervates the carotid sinus and carotid body, involved in the regulation of blood pressure Auricular – sensory innervation to a portion of the external ear and the external auditory canal. Visceral Motor (Parasympathetic) – fibers arise from the inferior salivatory nucleus ○ Pre-ganglionic fibers travel with the glossopharyngeal nerve and synapse in the otic ganglion ○ Post-ganglionic fibers innervate the parotid gland, stimulating salivation CN X (Vagus nerve): think of heart* when hearing vagus nerve Originates from several nuclei in the medulla oblongata ○ Dorsal motor nucleus of the vagus (autonomic) ○ Nucleus ambiguous (primarily somatic) Mixed nerve: somatosensory, somatomotory, viscerosensory, visceromotory fibers Somatosensory: general sensory + pain Somatomotor: striated muscles of pharynx, larynx esophagus  Viscerosensory: mucosa of the larynx, pharynx trachea, esophagus pleura, pericardium, lung stomach, organs present in the upper part of the abdominal cavity Visceromotor: glands of the upper-mentioned organs CN XI (Spinal accessory nerve): Part of fibers arise form the cervical spinal cord C1-C5 (somatic) and the nucleus ambiguous (autonomic) in the medulla Two components – cranial and spinal Cranial ○ Originates from the nucleus ambiguous ○ Travels briefly along with the vagus nerve and exits the skull through the jugular foramen and innervate muscle associated with swallowing and speech Palatoglossus Muscle – helps elevate the back of the tongue during swallowing, aiding in the swallowing reflex Levator veli palatini – helps elevate the soft palate during swallowing and prevents food from entering the nasopharynx Spinal ○ Originates from the spinal cord, C1 to C5 level or C6) ○ Motor neurons ascend through the foramen magnum to enter the cranial cavity, subsequently will exit the skull with cranial component through the jugular ○ Divides into branches that innervate the sternocleidomastoid and trapezius muscles ○ Functions Sternocleidomastoid Muscle – responsible for rotating the head and flexing the neck Trapezius Muscle – helps elevate the shoulders (shrugging) and assists with movements of the scapula ○ Clinical Damage to the spinal component result in weakness or atrophy leading to difficulties in head movement and shoulder elevation CN XII (Hypoglossal nerve): nucleus at the medulla oblongata involved in tongue activity Anything that goes into the gray matter of spinal cord or emerges from there are our spinal nerves  Their form is white matter (outside) and gray matter (inside) Motor nerve: muscles of the tongue, infrahyoid muscles Neck: between a. carotis comm. & int. Jugular vein ○ Lateral groove of the tongue ○ Ausa cervicalis Fibers exit the skull through the hypoglossal canal, a small opening located in the occipital bone Travels downward and forward to reach the tongue, running close to the carotid arteries and the internal jugular vein Innervates all the intrinsic and extrinsic muscles of the tongue, except for the palatoglossus muscle, which is innervated by the vagus nerve and the cranial part of the accessory nerve Its function can be assessed by asking the patient to stick out their tongue Damage to the hypoglossal nerve can result in dysarthria, dysphagia or atrophy tongue muscles CN Pathways and Functions Sensory nerves ○ Olfactory nerve (I) and optic nerve (II): outgrowth of the central nervous system; sometimes not considered true cranial nerves ○ Vestibulocochlear nerve (VIII) Motor nerves ○ IV, VI, XII: somatomotor (voluntary) ○ III: somatomotor, visceromotor (involuntary)- pupil at sphincter muscle Parasympathetic: pupil constriction and accommodation by ciliary muscle Mixed: ○ VII, IX, X: sensory, motor, somatic, and autonomic ○ V: sensory and motor somatic Special motor: ○ XI (motors- spinal fibers) General functionality  ○ Ophthalmic nerve (V1): Arises from the trigeminal ganglion. Branches: ○ Frontal Nerve: Largest branch Supraorbital Nerve – innervates the forehead and scalp Supratrochlear Nerve – innervates the skin of the forehead and medial part of the eyelid ○ Nasociliary Nerve Provides sensory innervation nasal cavity, cornea, and ciliary body Branches Infratrochlear Nerve - skin of upper eyelid and side of nose Ethmoidal Nerves – innervate the ethmoid sinus and nasal cavity ○ Lacrimal Nerve: Supplies sensory fibers to the lacrimal gland and carries parasympathetic fibers “hitchhiked” from the facial nerve (via the zygomatic branch of V2) to stimulate tear production Maxillary nerve (V2): Arises from the trigeminal ganglion Travels through the foramen rotundum, entering the pterygopalatine fossa Branches  ○ Zygomatic Nerve– sensation to the skin over the zygomatic (cheek) bone and contributes to the lacrimal nerve, which innervates the lacrimal gland ○ Infraorbital Nerve– largest branch; it exits through the infraorbital foramen and innervates the lower eyelid, upper lip, part of the nasal cavity and upper maxilla ○ Posterior Superior Alveolar Nerve– provides sensation to the maxillary molars and adjacent buccal mucosa ○ Middle Superior Alveolar Nerve– supplies the maxillary premolars and part of the maxillary sinus ○ Anterior Superior Alveolar Nerve– innervates the maxillary incisors and canine teeth and the associated gingiva Mandibular nerve: Arises from the trigeminal ganglion Travels through the foramen ovale to enter the infratemporal fossa Branches ○ Motor Branches– innervate the muscles of mastication Masseter Temporalis Medial and Lateral Pterygoid Muscles ○ Sensory Branches: Important sensory branches include: Buccal Nerve– buccal mucosa and skin over the cheek Auriculotemporal Nerve– supplies sensation to the skin in front of the ear and parts of the temple and carries autonomic fibers to the parotid gland Lingual Nerve– provides sensory innervation to the anterior two-thirds of the tongue and the floor of the mouth; also carries autonomic fibers from the facial nerve (VII) to the submandibular and sublingual glands Inferior Alveolar Nerve– supplies sensation to the lower teeth; it has a terminal branch (mental nerve), provides sensation to the chin and lower lip