Chapter 5 Peripheral Nervous SystemThe peripheral nervous system consists of thecord, they are divided into the 5 groups: 8 pairs ofcervical nerves,12 pairs of thoracic nerves,5 pairs onervous structures which are located outside the brainlumbar nerves, 5 pairs of sacral nerves and 1 pair ofand spinal cord. The peripheral nervous system iscomposed of nerves and ganglia. According to theircoccygeal nerves.Each spinal nerve is formed by an anterior root-origins, they are usually divided into two portions:and a posterior root which attach to the spinal cord.The cranial nerves which attach to the brain andThe anteriorroot contains motor fibers arising fromemerge out from the skull and the spinal nerves whichthe largemotorneurons inthe anteriorand lateralattach to the spinal cord and emerge out from thehorns of the gray matter.The posterior root containsvertebral canal. According to the distributions, theysensory fibers, which are the central processes of theare usually divided into the somatic nervous systempseudounipolar neurons in the spinal ganglion. Thus,which is distributed to the skin, joints, ligaments andthe spinal nerves are mixed nerves. The spinal gan-skeletal muscles etc,and the visceral nervous systemwhichglionis form an enlargement of the posterior root nearis distributed to the intemal organs.Actually the visceralthe intervertebral foramen.It contains pseudouni-nervous system is formed by visceral sensory and visceralpolar neurons which give off peripheral process-motorcomponents,the latter is called the visceral motores. The peripheral process unites with the ante-nerve, the autonomic nerve or vegetative nerve whichrior root to form the spinal nerve at the intervertebraltravels within certain spinal and cranial nerves to innervateforamen(Fig, VI-5-1),smoothmuscles,cardiacmuscleandglands.There are four types of fibers in the spinal nerves:Section 1SpinalSomatic afferentlsensorNervesfibersSpinal nerves consists of 31 pairs. According tothe regions that the nerves are attached to the spinalThey are the peripheral processes of the pseudoun-PosteriorrootSomatic sensory fiberSpinal ganglionSomaticsensoryfibeVisceral sensory fibersPosteriorbranchof spinal nVisceral motorfibersSomatic motorfibersGray communicutingbranchMuscle spindlWhite communicutingbranchGanglion of sympathetic trunkAnterior branch of spinal n.SkilVisceral organSkeletalmuscleFig. VI-5-1A diagram of the formation of spinal nerve·373-扫描全能王创建
·374·PARTVINERVOUSSYSTEMwith the sympathetic trunk.The posterior branchesipolar neurons in spinal ganglion and distributed toare generally smaller than the anterior,and the distri-the skin, skeletal muscles, tendons and articulationsbutions are segmental. The cutaneous branch from theof the trunk and limbs.They conduct the sensory in-posterior branch of the secondary cervical nerve isformation from those parts to the spinal cord.larger,which is named as the greater occipital nerveand is distributed to the occipital region..Somatic efferent(motor)fibersGenerally most of the anterior branches of thespinal nerves(except the thoracic nerves)form intri-They are axons of the somatic motor neurons incate plexus firstly,before supplying the structures ofthe anterior horn of the gray matter, innervate thethe body.The plexuses include the cervical plexus,skeletal muscles of the trunk and limbs and controlthe brachial plexus, the lumbar plexus and the sacro-the movement of the muscles.coccygeal plexus. Then many nerves arise from themand supply the definite parts of the body.The anterior3.Visceral afferent(sensory)fibbranches of thoracic nerves are separated from eachother and distributed to thethoracic and abdominalwall.They are also the peripheral processes of pseudoun-I.The Anterior Branches ofipolar neurons in spinal ganglia but distributed to thevisceral organs, cardiovascular system and glands,ThoracicNervesand transmit the sensory impulses from them to thecentralnervous system.There are twelve pairs of the thoracic nerve innumber(Fig.VI-5-2).The anterior branches of the4.Visceral efferent (motor)fibersupper eleven pairs lie in the corresponding intercostalspaces and are called the intercostal nerves, but theThesefibers arise from the visceral motor neuronslast pair lies below the twelfth rib, so it is called thein the lateral intermediate nuclei of gray matter, theysubcostal nerve.Theintercostal nerves run forwardare distributed to the smooth muscles of the visceralbetween the pleura and the internal intercostal mem-organs,cardiovascular system andglands,andcontrolbrane medial to the angles of the ribs. They then entertheir activities.the interval between the internal and external inter-All of the spinal nerves emerge out of the ver-costal muscles and traverse along the costal groove,tebral canal via the corresponding intervertebral fo-in company with the intercostal vessels and inferiorramina.However, the first cervical nerve emerges be-to them. The nerves are connected with the adjoiningtween the atlas and the occipital bone, the eighth oneganglion of the sympathetic trunk by gray and whiteemerges between the seventh cervical and the firstcommunicating branches (Fig. VI-5-1).thoracic vertebrae; the first four of the sacral nervesThe upper six intercostal nerves run toward theexitsthroughtheanteriorand posterior sacralforamsternum and terminate as the anterior cutaneousina,the fifth sacral and the coccygeal nerves emergebranches that pierce the intercotal muscles and thefrom the sacral hiatus.pectoralismajor near the sternumto supply the skinAfter leaving the intervertebral foramen, eachof the anterior thoracic wall.The lateral cutaneousspinal nerve is divided into four branches immediate-branches arise from the nerves near the costal angles,ly: @ An anterior branch which is distributed to thethey pierce the external intercostal and serratus ante-limbs and theventrolateral portion of thetrunk;②Ariormuscles,andaredivided intoanteriorandposteposterior branch supplying the structures of the pos-rior branches which are distributed to the skin of theterior region of the body. Above-mentioned branchesscapular region, the ventrolateral thoracic wall andcontain the fibers from the anterior and posteriorthe mammary gland.Their muscular branches supplyroots of the spinal cord;?Asmallmeningeal branchthe intercostal muscles and transverse thoracic mus-running back to the vertebral canal through the inter-cle(Fig. VI-5-3) .vertebral foramen and distribute to the dura mater;The lower five intercostal nerves and the subcostalone or two communicating branches, which connectnerve pass behind the costal arch and proceed forward扫描全能王创建
Chapter 5Peripheral Nervous System ·375 .into the abdominal wall between the obliquus inter-muscles, but also the transversus abdominis, obliquusnus abdominis and transversus abdominis. Then theyinternus abdominis, obliqus externus abdominis andpierce the sheathofrectus abdominis and terminate asrectus abdominis. The cutaneous branches are distrib-anterior cutaneous branches near the linea alba. Theiruted to the skin of abdominal and lower part of themuscular branches not only supply the intercostalthoracic walls(Fig. VI-5-2)T10T12Iliohypogastric n.Ilioinguinal nFig. VI-5-2 The distributions of the anterior branches of thoracic nervescriorbranchIntercostales externiIntercostales interniAnteriorbranchLateral cutaneousbrIntercostales intimiAnteriorcutaneousbrFig. VI-5-3 A diagram of a typical thoracic nerve扫描全能王创建
·376·PARTVINERVOUSSYSTEMThe distribution of the anterior branches of thethoracic nerves are segmental(Fig. VI-5-2) . On theII.The Cervical Plexuschest and anterior-lateral abdominal wall, they pres-ent approximately at thelevels as follows:1.Position and formation ofT,—the level at the sternal angleT,the level at the nipplecervical plexusTthe level at thexiphoid processTthe level between the xiphoid process and theThe cervical plexus is deep to the upper part of theumbilicussternocleidomastoid and ventrolateral to the levatorTro—the level at the umbilicusscapulae and the scalenus medius. It is formed by theTi2—the level at the anterior superior iliac spineanterior branches of the frst four cervical nerves(C,)(Fig. VI-5-4) .lypoglossaln.LeSuperior cervicalganglionoccipital n,ofsympathetictrunkGreater auricular n.Transverse n.of neoAnsacervicalisPhrenicn.Supraclavicular n.Fig. VI-5-4A diagram ofthe formation of cervical plexus and its branchesthe posterior border of the sternocleidomastoid andBranches of cervical plexusdistribute to the skin of the mastoid region.2) Great auricular nerve(C23) It runs upwardover the sternocleidomastoid to the auricle and pa-The branches of the cervical plexus may be divid-rotid gland regions, usually along with the externaled into superficial and deep groups.jugular vein. It supplies much of the external ear andskin around the auricle.(1) Superficial branches3) Transverse nerve of neck(C2.5)It winds aro-und the posterior border of the sternocleidomastoidThey emerge near the midpoint of the posteriorabout its midpoint and runs forward to reach the ante-border of the sternocleidomastoid and are describedriortriangleoftheneck.It isdistributedtothe skinofas follows:(Fig. VI-5-5).the anterior region of the neck.1) Lesser occipital nerve(C) It ascends along扫描全能王创建
Chapter 5 Peripheral Nervous System - 377 .The muscular branches supply the deep muscles4) Supraclavicular nerve(C,-)It emerge be-ofthe neck, such as the levator scapulae, scalenus andlow the transverse nerve of neck and descend in theprevertebral muscles. A part of the nerve fibers fromposterior triangle of the neck where it gives off threethe cervical plexus join together to form the inferiorbranches: the lateral, intermediate and medial supra-root of the ansa cervicalis which unites with the de-clavicular nerves which are distributed to the skin atthe upper portion of the chest, theroot of the neckscending branch of the hypoglossal nerve, to formthe ansa cervicalis. Then the ansa cervicalis gives offand the shoulder.branches to supply the omohyoid, sternohyoid, ster-(2) Deep branchesnothyroid and thyrohyoid muscles.EThe phrenic nerve arises from the third, fourth andThe deep branches of the cervical plexus includefifth cervical nerves of the cervical plexus.It passesthe muscular branches; inferior root of the ansa cervi-downward in front of the scalenus anterior to the rootcalis and the phrenic nerve(Fig. VI-5-6)Greater occipitalStermocleidomastoidLesser occipital n.Cervical br. of facial n.Greater auricular rCommunicating br.PlatismaExtermal br.of accessory nTransveerse n.of neckLateral supraclavicular n.Anterior jugular y.External jugular v.Medial supra-clavicular n.Intermedial supraclavicular n.Fig. VI-5-5 The superficial branches of cervical plexusof the neck, then descends between the subclavianartery and vein to enter the chest. Within the chest itII . Brachial Plexusdescends in front of the root of the lung, between thepericardium and the mediastinal pleura, to the dia-phragm. The phrenic nerve contains motor and sen-Position and formation of thesory fibers. The motor fibers supply the muscle of thediaphragm; the sensory fibers are distributed to thebrachial plexuspericardium, the diaphragmatic pleura and mediasti-nal pleura, and the diaphragmatic peritoneum. The sen-The brachial plexus emerge from the intervalsory fibers of the right phrenic nerve are also distributedbetween the scalenus anterior and scalenus medi-to the liver, the gallbladder and the bile duct system.us which is called the scalene fissure, then extendsoutward and downward behind themedial 2/3 of the扫描全能王创建