Y khoa, y dược - The peripheral nervous system and reflex activity: Part B

13 The Peripheral Nervous System and Reflex Activity: Part BCranial NervesTwelve pairs of nerves associated with the brain Most are mixed in function; two pairs are purely sensoryEach nerve is identified by a number (I through XII) and a name“On occasion, our trusty truck acts funny—very good vehicle anyhow”Figure 13.5 (a)Frontal lobeTemporal lobeInfundibulumFacialnerve (VII)Vestibulo-cochlearnerve (VIII)Glossopharyngealnerve (IX)Vagus nerve (X)Accessory nerve (XI)Hypoglossal nerve (XII)(a)Filaments ofolfactory nerve (I)Olfactory bulbOlfactory tractOptic chiasmaOptic nerve(II) Optic tractOculomotornerve (III)Trochlearnerve (IV) Trigeminalnerve (V) Abducensnerve (VI)CerebellumMedullaoblongata Figure 13.5 (b) *PS = parasympathetic(b)Cranial nervesI – VIIIIIIIIVVVIOlfactoryOpticOculomotorTrochlearTrigeminalAbducensYes (smell)Yes (vision)NoNoYes (generalsensation)NoNoNoYesYesYesYesNoNoYesNoNoNoCranial nervesVII – XIISensoryfunctionMotorfunctionPS*fibersSensoryfunctionMotorfunctionPS*fibersVIIVIIIIXXXIXIIFacialVestibulocochlearGlossopharyngealVagusAccessoryHypoglossalYes (taste)Yes (hearingand balance)Yes (taste)Yes (taste)NoNoYesSomeYesYesYesYesYesNoYesYesNoNoI: The Olfactory NervesArise from the olfactory receptor cells of nasal cavityPass through the cribriform plate of the ethmoid boneFibers synapse in the olfactory bulbsPathway terminates in the primary olfactory cortexPurely sensory (olfactory) functionTable 13.2II: The Optic NervesArise from the retinasPass through the optic canals, converge and partially cross over at the optic chiasmaOptic tracts continue to the thalamus, where they synapseOptic radiation fibers run to the occipital (visual) cortexPurely sensory (visual) functionTable 13.2III: The Oculomotor NervesFibers extend from the ventral midbrain through the superior orbital fissures to the extrinsic eye musclesFunctions in raising the eyelid, directing the eyeball, constricting the iris (parasympathetic), and controlling lens shapeTable 13.2IV: The Trochlear NervesFibers from the dorsal midbrain enter the orbits via the superior orbital fissures to innervate the superior oblique musclePrimarily a motor nerve that directs the eyeballTable 13.2V: The Trigeminal NervesLargest cranial nerves; fibers extend from pons to faceThree divisions Ophthalmic (V1) passes through the superior orbital fissure Maxillary (V2) passes through the foramen rotundumMandibular (V3) passes through the foramen ovaleConvey sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for masticationTable 13.2Table 13.2VI: The Abducens NervesFibers from the inferior pons enter the orbits via the superior orbital fissuresPrimarily a motor, innervating the lateral rectus muscleTable 13.2VII: The Facial NervesFibers from the pons travel through the internal acoustic meatuses, and emerge through the stylomastoid foramina to the lateral aspect of the faceChief motor nerves of the face with 5 major branchesMotor functions include facial expression, parasympathetic impulses to lacrimal and salivary glandsSensory function (taste) from the anterior two-thirds of the tongueTable 13.2Table 13.2VIII: The Vestibulocochlear NervesAfferent fibers from the hearing receptors (cochlear division) and equilibrium receptors (vestibular division) pass from the inner ear through the internal acoustic meatuses, and enter the brain stem at the pons-medulla borderMostly sensory function; small motor component for adjustment of sensitivity of receptors Table 13.2IX: The Glossopharyngeal NervesFibers from the medulla leave the skull via the jugular foramen and run to the throatMotor functions: innervate part of the tongue and pharynx for swallowing, and provide parasympathetic fibers to the parotid salivary glandsSensory functions: fibers conduct taste and general sensory impulses from the pharynx and posterior tongue, and impulses from carotid chemoreceptors and baroreceptors Table 13.2X: The Vagus NervesThe only cranial nerves that extend beyond the head and neck regionFibers from the medulla exit the skull via the jugular foramenMost motor fibers are parasympathetic fibers that help regulate the activities of the heart, lungs, and abdominal visceraSensory fibers carry impulses from thoracic and abdominal viscera, baroreceptors, chemoreceptors, and taste buds of posterior tongue and pharynx Table 13.2XI: The Accessory NervesFormed from ventral rootlets from the C1–C5 region of the spinal cord (not the brain) Rootlets pass into the cranium via each foramen magnumAccessory nerves exit the skull via the jugular foramina to innervate the trapezius and sternocleidomastoid musclesTable 13.2XII: The Hypoglossal NervesFibers from the medulla exit the skull via the hypoglossal canal Innervate extrinsic and intrinsic muscles of the tongue that contribute to swallowing and speechTable 13.2