Cranial Nerves PDF

 CRANIAL NERVES GSE (motor) – receive fibers from motor areas cortex through corticonuclear fibers GSA (sensory) – spinal nucleus of the trigeminal nerve GVA (visseral sensations) – nucleus of the tractus solitarius GVE (parasympathetic) – private parasympathetic nuclei SVE (m...

 CRANIAL NERVES GSE (motor) – receive fibers from motor areas cortex through corticonuclear fibers GSA (sensory) – spinal nucleus of the trigeminal nerve GVA (visseral sensations) – nucleus of the tractus solitarius GVE (parasympathetic) – private parasympathetic nuclei SVE (motor to branchiomeric muscles) – private for CN V and VII, nucleus ambiguus for IX, X, XI SSA (visiual, auditory, equilibrium) SVA (taste, smell) – taste (upper part of nucleus of the tractus solitarius – gustatory nucleus)  Cranial nerves conveying sensory fibers have sensory ganglia outside the central nervous sytem where the cell bodies of the first order neurons lie – i.e trigeminal ggl., geniculate ganglion, spiral ggl., vestibular ggl. Motor nuclei of the cranial nerves receive corticonuclear fibers from both hemispheres Except Part of facial nucleus responsible for the innervation of lower part of the face Part of hypoglossal nucleus responsible for the innervation of the genioglossus muscle Parasympathetic nuclei of the cranial nerves receive afferent impulses from hypothalamus through descending autonomic pathways (route unknown)  OLFACTORY NERVE Olfactory receptor cells Olfactory nerves Olfactory bulb Mitral and tufted cells Olfactory tract Medial and lateral olfactory stria  Medial olfactory stria carries fibers that cross at the anterior comissure to terminate in the cotralateral olfactory bulb Lateral olfactory stria carries fibers that reach the olfactory areas of the cortex Olfactory areas Primary olfactory cortex - periamygdaloid and prepyriform areas Secondary olfactory cortex – entorhinal area (Bodmann 28)  Olfaction bears crucial importance in lower mammals – Mating – Reproducing – Finding food – Sensing danger Clinical note Anosmia Infections of the olfactory mucosa Damage to the olfacotry nerves, bulb and tract may lead to unilateral anosmia Fractures of the cribriform plate of the ethmoid bone  OPTIC NERVE Optic receptor cells Cones (vision in the light, clear and colour vision) Rods (vision in the dark) Bipolar cells Ganglion cells  Macula lutea (central vision-mostly cones) Fovea centralis (most clear vision – only cones) Visual field Optic nerve Optic chiasm Optic tract Lateral geniculate body Optic radiation Optic radiation passes through the retrolentiform part of the internal capsule Meyer’s loop Conveys fibers from cotralateral lower quadrant of the retina (cotralateral upper quadrant of the visual field) Lesions and associated blindness in the visual fields Visual reflexes Direct and consensual light reflexes Accomodation reflex Visual body reflexes (scanning objects, protective closing of the eyes etc.) Corneal reflex (blink reflex) – not vision related Pupillary skin reflex (painful stimulation of the skin – not vision related) Pathway for direct and consensual light reflex Lesions may lead to anisocoria OCULOMOTOR NERVE Has two nuclei Motor nucleus Innervates the five of the seven extrinsic eye muscles Parasympathetic nucleus (accesory nucleus, Edinger Westphal nucleus) Ciliary ganglion Short ciliary nerves Constrictor pupilla and ciliary muscles Medial longitudinal fasciculus MLF Connects the 3rd, 4th, 6th and 8th cranial nerves Clinical note Oculomotor nerve palsy Paralysisof the related eye muscles Eye is deviated to the lateral side Diplopia Ptosis Mydriasis (dilated pupil) Impairment of pupillary light reflex Impairment of accommodation convergence reflex  Pupillary light reflex Direct and indirect (consensual) Accommodation convergence reflex (focus to a near object) Both medial rectus muscles contract Both pupils constrict A-P diameter of the lenses increase (ciliary muscles) Oculomotor nerve  TROCHLEAR NERVE Motor nucleus Innervates the superior oblique muscle Only cranial nerve that leaves the brainstem through its posterior aspect Crosses to the other side as it emerges from the brainstem.  TRIGEMINAL NERVE Motor nucleus Main sensory nucleus Spinal nucleus Mesencephalic nucleus  Motor nucleus Supplies the muscles of mastication, tensor tympani, tensor veli palatini, mylohyoid and anterior belly of the digastric  Sensory nuclei Receives somatic sensations from the skin of the face and mucous membranes. Axons in the trigeminal nerve related with somatic sensations (except the proprioception) have their cell bodies in the trigeminal ganglion (semilunar ganglion). Propriceptive fibers ascend to reach the mesencephalic nucleus. Touch and pressure fibers ascend to reach the main sensory nucleus. Pain and temperature fibers enter the spinal nucleus. All fibers cross and ascend as the trigeminal lemniscus to reach the VPM of thalamus where they will be relayed to the postcentral gyrus (areas 3, 1, 2)  Ophthalmic (V1) – sensory – superior orbital fissure Maxillary (V2) – sensory – foramen rotundum Mandibular (V3) – sensory and motor – foramen ovale  ABDUCENT NERVE Motor nucleus Innervates the lateral rectus muscle Clinical note Abducent nerve palsy Paralysis of the lateral rectus muscle Medial strabismus (eye is deviated to the medial side) Horizontal diplopia Lateral gaze palsy Oculomotor internuclear ophthalmoplegia Due to the lesion of MLF May be unilateral or bilateral Fibers extending from abducent nuclei to contralateral medial rectus subgroup of oculomotor nucleus are damaged. On attempted lateral gaze the lateral rectus of one side contracts, however contralateral medial rectus can not contract.  FACIAL NERVE Motor nucleus Parasympathetic nuclei Superior salivatory nucleus Sensory nucleus is the nucleus of the solitary tract (common sensory nucleus of CN 7, 9 and 10)  Sensory and parasympathetic fibers are carried by the nervus intermedius.  Motor nucleus Supplies the muscles of facial expression, stapedius muscle, posterior belly of the digastric muscle and stylohyoid muscle. Part of the facial nucleus responsible for the innervation of lower part of the face recieves only unilateral corticonuclear fibers from the contralateral side  Parasympathetic nuclei Superior salivatory nucleus supplies the submandibular and sublingual salivary glands, as well as the nasal and palatine glands Lacrimal nucleus supplies the lacrimal gland Nucleus of the solitary tract Receives taste sensation from the facial nerve (2/3 anterior part of the tongue) as well as glossopharyngeal and vagus nerves. Taste fibers have their first order neurons in the geniculate ganglion. Course of the facial nerve Internal acoustic meatus Facial canal – Geniculate ganglion Stylomastoid foramen Clinical note Facial nerve palsy In central type lesions, contralateral lower part of the face is affected. Bell’s palsy is a peripheral dysfunction of the facial nerve, often associated with the swelling of the nerve in the facial canal. VESTIBULOCOCHLEAR NERVE Vestibular nerve Cochlear nerve  Vestibular nerve Receptor cells are in the inner ear Ampulla of the semicircular canals and macula of the utricle and saccule Vestibular nerve and vestibular ganglion (within the internal acoustic meatus) Vestibular nuclei Lateral, medial, superior, inferior Connections of the vestibular nerve Receive afferent fibers from the cerebellum through the inferior cerebellar peduncle Send efferent fibers to the cerebellum which also pass through the inferior cerebellar peduncle Send uncrossed vestibulospinal tract to the spinal cord – Information from inner ear assist in maintaining balance by influencing muscle tone of the limbs and trunk Send efferent fibers to the CN 3, 4 and 6 – Coordinated movements of the head and eye for visual fixation on objects Ascending fibers to the vestibular areas of the cerebral cortex (postcentral gyrus) – probably relayed in VPL of thalamus  Clinical note Disturbances of vestibular nerve function Vertigo and nystagmus – Vertigo is due to inappropriate impulses incoming to (Meniere’s disease) or arising from the vestibular nuclei – Vestibular nuclei are connected to the CN 3, 4 and 6 by the MLF. Lesions of the vestibular system or MLF will lead to nystagmus due to the impairment of control of the eye muscles (cerebellar lesions also produce nystagmus)  Cochlear nerve Receptor cells are in the cochlea, at the organ of Corti Spiral ganglion (within the modiolus of cochlea) Cochlear nerve passes through the internal acoustic meatus Anterior and posterior cochlear nuclei  Auditory pathway Cochlear nuclei (2nd order neuron) Posterior nucleus of the trapezoid body – Being mostly from contralateral, receives bilateral fibers from the cochlear nuclei Lateral lemniscus Nucleus of lateral lemniscus (some fibers are relayed here) All fibers finally synapse in the inferior colliculus, where they are relayed to the medial geniculate body The fibers starting from the medial geniculate body form the acoustic radiation and terminate in the primary auditory area of cortex (primary auditory area - Brodmann 41, 42) Acoustic radiation passes through the sublentiform part of the internal capsule  Clinical note Disturbances of cochlear nerve function Deafness and tinnitus (ability of hearing a whispered voice should be tested) Deafness may be due to – Defect in the conducting mechanism of the middle ear (coductive type deafness) – Organ of corti, cochlear nerve, cochlear nuclei, lateral lemniscus or auditory cortical areas (sensory-neural deafness) Unilateral damages to the lateral lemniscus or the auitory cortex produce bilateral partial deafness which is more prominent on the contralateral side. GLOSSOPHARYNGEAL NERVE Motor nucleus Nucleus ambiguus (common motor nucleus for CN 9, 10 and 11) Parasympathetic nucleus Inferior salivatory nucleus Sensory nucleus Nucleus of the solitary tract (common sensory nucleus of CN 7, 9 and 10) Pharyngeal plexus Motor 9, 10, 11 Sensory 9, 10  Motor nucleus Supplies the stylopharyngeus muscle Fibers also contribute the pharyngeal plexus Parasympathetic nucleus Referred as the inferior salivatory nucleus Supplies the parasympathetic innervation of the parotid gland Route  Tympanic nerve – tympanic plexus – lesser petrosal nerve – otic ganglion – auriculotemporal nerve – parotid gland  Sensory nucleus Nucleus of the tractus solitarius Has two sensory ganglia (both lie at the level of the jugular foramen) – Superior ganglion (GSA fibers have their cell bodies here) – Inferior ganglion (SVA and GVA fibers have their cell bodies here) GSA fibers (from auricle) pass to the spinal nucleus of the trigeminal nerve SVA fibers (from 1/3 post of the tongue) and GVA fibers (sensory information from pharynx through the pharyngeal plexus) terminate in the nucleus of the tractus solitarius GVA fibers from carotid sinus (baroreceptors) and carotid body (chemoreceptors) also terminate in the nucleus of the tractus solitarius where they are relayed to the parasympathetic nucleus of the vagus nerve (completing the loop for the reflex)  VAGUS NERVE Motor nucleus Nucleus ambiguus (common motor nucleus for CN 9, 10 and 11) Parasympathetic nucleus Referred as the dorsal nucleus of vagus Sensory nucleus Nucleus of the solitary tract (common sensory nucleus of CN 7, 9 and 10)  Motor nucleus Supplies the constrictor muscles of the pharynx (through the pharyngeal plexus) and the intrinsic muscle sof the larynx (through the superior and inferior laryngeal nerves) Parasympathetic nucleus Supply the parasympathetic innervation of the organs in the thorax as well as the abdominal organs and alimentary tract as far as the distal 1/3 of the transverse colon.  Sensory nucleus Nucleus of the tractus solitarius Has two sensory ganglia (both lie at the level of the jugular foramen) – Superior ganglion (GSA fibers have their cell bodies here) – Inferior ganglion (SVA and GVA fibers have their cell bodies here) GSA fibers (from auricula) pass to the spinal nucleus of the trigeminal nerve SVA fibers (from most posterior part of the tongue) and GVA fibers (sensory information from larynx and soft palate) terminate in the nucleus of the tractus solitarius  ACCESSORY NERVE Motor nucleus formed of cranial and spinal roots Cranial root is from nucleus ambiguus Spinal root is from the spinal nucleus of the nerve (lie lateral to the anterior gray horn within the first five segments of the spinal cord) Cranial root joins the vagus nerve and contribute to the joins the pharyngeal plexus Spinal root innervates the SCM and trapezius muscles  HYPOGLOSSAL NERVE Motor nucleus Innervates the intrinsic muscles of the tongue as well as the styloglossus, the hyoglossus and the genioglossus muscles Part of the hypoglossal nucleus responsible for the innervation of the genioglossus muscle recieves only unilateral corticonuclear fibers from the contralateral side Clinical note Damage to the hypoglossal nerve – Tongue will deviate to the side of the lesion when prodruded. Interruption of the corticonuclear fibers coming to the hypoglossal nuscleus will only effect the genioglossus muscle. – Tongue will deviate to the contralateral side of the lesion when prodruded.