Chapter2Central Nervous System ·303 .the early stages ofthis condition,dcussatingmosifxousebers for pain and temperature in the ventral whitetcocommissure are damaged selectively; this resultsdnahwyadin a loss of pain and temperature sense. Becausebowelfunctionsarnlongerunderoluntaryof the location of the cavity, the axons of the dor-control.sal columns are spared, and therefore touch and(2) spinal cord hemisection Complete he-limb position senses are unaffected. It is calledmisectionofthecord produces aBrown-Sequarddissociated anesthesia. Syringomyelia interruptsyndromaesultobuletorstabwoundsdecussating axons from both sides of the body,ygmyinmhence, the sensory loss that occurs is usuallyetc.bilaterally symmetrical. Cavity formation occursThe main signs and symptoms include:most commonlyin the cervical and upperthorac1) Ipsilateral spastic paralysis of the musclesic spinal segments,therebyproducing a cape-likebelow the level of the lesion;distribution of sensory loss on the arms, shoulder,2) Ipsilateral loss of proprioceptive, vibrato-and upper trunk (Fig. VI-2-13) .y and twopoint discriminationsense below thelevel of the lesion;3) Contralateral loss of pain and temperaturesense below the lesion.The motor deficits of distal limb are all ex-pressed on the ipsilateral side because the lateralcorticospinal tract (descending motor pathways),which target distal limb muscle motor neurons,decussate in the brain stem. Because the medialdescendingpathwaysterminatebilaterally,axialmotor function is usually not seriously affectedwith unilateral spinal cord lesions.Axons in the dorsal columns are uncrossedin the spinal cord; hence deficits in touch andlimb position sense are present ipsilateral to thespinal cord lesion. In contrast, the axons of theventrolateral system decussate in the spinal cord.Therefore, pain and temperature senses are im-paired on the side ofthe body that is contralateralto the lesion.(3) Ventral horn lesion It produces theFig.VI-2-13 Distribution of loss of pain andtemperature sense over body insyringomyeliasigns of LMN lesions described as above. Typi-involving the cervicothoracic portion of the spinalcal causes include poliomyelitis, in which a viruscordselectively attacks ventral horn cells or equiva-lent neurons in the brain stem, with no sensorySun Jinhao（孙晋浩）modalities being involved.(4) Lesions in the central portion of theSection2:Brain Stemspinal cord Asmall central lesion of the spi-nal cord occurs, for example, in syringomyeliaThe brainstem is made up of the medulla oblonga-whichisonetypeofthedegenerativediseasesofta, the pons, and the midbrain. It is stalklike in shapethe CNS.In this pathological process,acavityand connects the narrow spinal cord with the expand-fomthntralrininaoded forebrain. The superior boundary of brainstem is扫描全能王创建
·304·PART VI NERVOUS SYSTEMoptic tract, while its inferior boundary is the upperborder of the first cervical nerve roots.I . External AppearanceThe brainstem participates in three broad func-tions: @ It serves as a conduit for the ascending anddescending tracts connecting the spinal cord to theMedulla oblongatadifferent parts of the brain. It contains importantreflex centers associated with the control of respira-The medullaoblongataconnects the pons superi.tion and the cardiovascular system; it also is associ-ly with thespnalcodiferoy(Fig214,)ated with the control of consciousness.③It containsThe junction of the medula and spinal cord is at thethe important nuclei of cranial nerves II through XIlevel of the foramen magnum.The medlla oblongataThe purpose of this section is to review the struc-is conical in shape, its broad extremity being directedture of the different parts of the brainstem so that thesuperiorly.The central canalofthe spinalcord continstudent can understand the spatial relationships ofues upward into the lower half of the medulla; in thethese parts to one another;thevarious connections ofupper half of the medulla it expands as the cavity ofthese parts are dealt with elsewhere as indicated in thetext.the fourth ventricle.orticopinal tractOpitic chiasmagOculomotorn.Trigeminal n.Abducent nFicial n.Vestibulocochlearn.Hgpoglosal nAccessorgnPyramidal decussationLateral corticospinal tracVentral corticospinal tract.to limb musclesto proximal musclesFig. VI-2-14 The ventral surface of the brain stem扫描全能王创建
Central Nervous System·305 .Chapter 2Internal capsuleCaudate nucleusDorsal thalamusTerminalstriaThird ventricleHabenulartrigonePineal bodyPulvinarlateral geniculateSuperior colliculusbodyInferiorcolliculusandbrachium of inferior colliculusSuperior(Anterior)Locus ceruleusmedullary velumMedialeminence_SuperiorcerebellarpeduncleSulcus limitans-Middle cerebellarpeduncleFacial colliculusStriae medullaresVestibular areaMedian sulcusInferior cerebellar peduncleHypoglossal triangleVagal triangleCuneate tubercleAreapostremaGracile tuberclePosterior median sulcusFig. V-2-15 The dorsal surface of the brainstemthe midline there is an elongated swelling, the gracileFrom anterior view, on the anterior surface oftubercle, produced by the underlying gracile nucleus.the medulla is the anterior median fissure,which isLateral to the gracile tubercle is a similar swelling,continuous inferiorly with the anterior median fissurethe cuneate tubercle, produced by the underlying cu-of the spinal cord.Oneach side of themedianfissureneate nucleus. Superior to the gracile tubercle is thethere is a swelling called the pyramid. The pyramidsinferior cerebellar peduncle.are composed of bundles of corticospinal nervefibersthat originate in large nerve cells in the precentralgyrus of the cerebral cortex.The pyramids taper infe-Ponsriorly,and it is here that the majority ofthe descending fibers cross over to the opposite side, formingThe pons is anterior to the cerebellum and con-the decussation of the pyramids. Posterolateral to thenects the medulla oblongata to the midbrain. It ispyramids are the olives, which are oval elevationsabout2.5mmlong.Theponsis superiortotheme-produced by the underlying inferior olivary nuclei. Indulla oblongata and is separated from it by bulbopon-the groove between the pyramid and the olive emergetine sulcus (Fig. VI-2-14, 15) .therootletsofthe hypoglossalnerve.PosteriortotheThe anterior surface is convex from side to sideolives are the inferior cerebellar peduncles, whichand shows many transverse fibers that converge onconnect the medulla to the cerebellum. In the grooveeach side toform the middle cerebellar peduncle.Thebetween the olive and the inferior cerebellar peduncleshallow groove in the midline, the basilar groove,emerge the roots of the glossopharyngeal and vaguslodges the basilar artery.On the anterolateral surfacenerves and the cranial roots of the accessory nerveof theponsthetrigeminal nerveemerges on eachside. Each nerve consists of a smaller, medial motorfrom superior to inferior.'The posterior surface of the superior half of theroot and a larger,lateral sensory root. In the bulbo-medullablongata,thecentralcanalofspinalcdpontine sulcus, there emerge,from medial to lateral,openstofoms thelowerpartofthefoorofthfourththe abducent, facial, and vestibulocochlear nerves.Ventricle (rhomboidfoa)The posteriorsurfaceThe posterior surface of the pons is hidden fromtheinferiorhalfofthemedulla iscontinuuswiththeview by the cerebellum. It forms the upper half of theposterior aspect of the spinal cord. On each sideof扫描全能王创建
·306·PARTVI.NERVOUSSYSTEMfloor of the fourth ventricle and is triangular.colliculusthlaeralgnculatebyandtheoctract.Theinferorbrachiumonnectstheinferioroliculus to the medial geniculate body.3.MidbrainOn the anterior aspect of the midbrain(Fig V-2.14)threisadeedression inthemidine, theinThe midbrain measures about 2 cm in length andteduncularossawhhibunddonithersconnects the pons and cerebellum with theforebrain.by the crus cerebri.The oculomotor nerve emergesThe midbrain is traversed by a narrow channel, thefrom tile medial side of the crus cerebri and passescerebral aqueduct, which is filled with cerebrospinalforward in the lateral wall of the cavermous sinus.fuid (Fig. VI-2-14, 15).On the dorsal surface of brain stem, there areOn theposterior surface of the midbrain,theretheepairs of cerebellar peduncles: superio, middeare twopairs of rounded eminences, which are fourand inferior, which connect the brain stem with thecolliculi (termed quadrigeminal body, corpora quad-cerebellum.rigemina) , They are divided into superior and infe-rior pairs by a vertical and a transverse groove. TheRhomboid fossasuperior colliculi are centers for visual reflexes, andthe inferior are lower auditory centers. Inferior to theIn the upper part of medulla oblongata and theinferior colliculus is the superior (anterior) medul-laryvelum,from which the trochlearnerveemerges.lower part of pons, the central canal of spinal cordThe trochlear nerve is the only one cranial nerve thatopens to form the fourth ventricle, which floor is theemergesfromthedorsal surfaceofbrain stem.Theserhomboid fossa (Fig. VI-2-15, 16). Its rostral angle isare delicate nerves that wind around the lateral aspectcontinuous with mesencephalic (cerebral) aqueductof the midbrain to enter the lateral wall of the cavern-The aqueduct pierces the midbrain and connects theous sinus.third ventricle with the fourth ventricle. At certainOn the lateral aspect of the midbrain,the superiorsites of the fourth ventricular walls, the cerebral piaand inferior brachia ascend in an anterolateral direc-mater and its blood vessels combine with the ependy-tion. The superior brachium passes from the superiorma to from the choroid tela. The blood vessels of theSuperior colliculusMedial geniculate bodyLateral geniculatebodyBrachium of inferior colliculusInferior colliculusTrochlear n.Cerebral peduncleTrigonum lemnisciSuperiormedullaryvelumSuperior cerebellar peduncleFourth ventricleMiddlecerebellar peduncleInferior(posterior)Inferior cerebellarmedullaryvelumpeduncleLateralforaminaChoroid plexusChoroid tissueMedian foramenCuneate tubercleGraciletubercleFig. V-2-16 The choroid of the fourth ventricle扫描全能王创建
Chapter2 Central Nervous System · 307 .otahtbararmedullares, on each side of the median sulcus, theremeraddyahelnare two triangular areas. The medial one is the hypo-sesooiiohebglossal triangle (contains hypoglossal nucleus), thelateral one is the vagal triangle (contains dorsal nucle-esoexwhastrrestoprothecbralpnalus of vagus nerve) (Fig. VI-2-15).The striae medllaresruntransversely betweenmidlinanthlaralanglethoaII . Internal Structureposerorsurfamitedlaterayythuerereearpedunclesadisdividdsym-halves byamediansulcus. Lateral tothis suleusisGeneral descriptionnngatedatiomdialmnwhLsboundedlateralybysulcuhesulcuslmtan.As in the spinal cord, the brainstem consists ofAdjacenttothetopofthesulcuslimitans isthelocuswhite matter (ascending and descending tracts)graycerlus.Neartheupperborderofthe striaemedulmatter (cranial nerve nuclei and non-cranial nervelares, the inferior end of the medialeminence isnuclei),and reticularformation,buta studyof trans-slightly expanded toform the facial colliculus, whichverse sections of this region shows that they haveisproduced by theroot ofthefacialnerve windingbeen extensively rearranged.around the nucleus of the abducent nerve (genu offacial nerve) and abducent nucleus. The floor of the(1) Nuclei of cranial nervessuperior partofthe sulcus limitans isbluish-gray andis called the substantia ferruginea; it owes its color toThe nuclei of cranial nerves of brain stem are re-a group of deeply pigmented nerve cells. Lateral tolated to the I-XII thpairs ofcranial nerves andformthe sulcus limitans is the area vestibuli produced bylongitudinalfunctioncolumns inthebrain stem.Accord-the underlying vestibular nuclei. On the lateral angleing their characters (functions and fiber connections),of the vestibular area is the auditory tubicle, whichthey are divided into 7 groups (Fig. VI-2-17, 18):contains the dorsal cochlear nucleus. Below the striaeAccessorynucleusofoculomotorn.Nucleus of oculomotor nerve(Edinger-Westphal's nucleus)Mesencephalic nucleus ofNucleus of trochlear nervetrigeminal nervePontine nucleus oftrigeminal nerveMotor nucleus of trigeminal n.Nucleus of abducent nerveNucleus of facial nerveCochlear nucleiSup.and inf. salivatory nucleiVestibular nucleiNucleus ofhypoglossal nerveNucleus ambiguusNucleus of solitary tractDorsal nucleus of vagus nerveSpinal nucleus of trigeminal nerveSpinal cordAccessory nucleusFig-henuceraaesithebainstem (dorsalw扫描全能王创建