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

13 The Peripheral Nervous System and Reflex Activity: Part CSpinal Nerves31 pairs of mixed nerves named according to their point of issue from the spinal cord8 cervical (C1–C8)12 thoracic (T1–T12)5 Lumbar (L1–L5)5 Sacral (S1–S5)1 Coccygeal (C0)Figure 13.6CervicalnervesC1 – C8ThoracicnervesT1 – T12LumbarnervesL1 – L5Sacral nervesS1 – S5Coccygeal nerve Co1Cervical plexusIntercostalnervesCervicalenlargementLumbarenlargementCauda equinaBrachial plexusLumbar plexusSacral plexusSpinal Nerves: RootsEach spinal nerve connects to the spinal cord via two rootsVentral rootsContain motor (efferent) fibers from the ventral horn motor neuronsFibers innervate skeletal muscles)Spinal Nerves: RootsDorsal rootsContain sensory (afferent) fibers from sensory neurons in the dorsal root gangliaConduct impulses from peripheral receptorsDorsal and ventral roots unite to form spinal nerves, which then emerge from the vertebral column via the intervertebral foraminaFigure 13.7 (a)Dorsal rootganglionGray matterWhite matterVentral rootDorsal rootDorsal andventral rootlets of spinal nerveDorsal ramusof spinal nerveVentral ramusof spinal nerveSympathetic trunkganglionSpinal nerveRami communicantesAnterior view showing spinal cord, associated nerves, and vertebrae. The dorsal and ventral roots arise medially as rootlets and join laterally to form the spinal nerve.Spinal Nerves: RamiEach spinal nerve branches into mixed ramiDorsal ramusLarger ventral ramusMeningeal branchRami communicantes (autonomic pathways) join to the ventral rami in the thoracic regionSpinal Nerves: RamiAll ventral rami except T2–T12 form interlacing nerve networks called plexuses (cervical, brachial, lumbar, and sacral)The back is innervated by dorsal rami via several branchesVentral rami of T2–T12 as intercostal nerves supply muscles of the ribs, anterolateral thorax, and abdominal wallFigure 13.7 (b)Dorsal ramusVentral ramusIntercostal nerveSpinal nerveRami communicantesDorsal rootganglion Dorsal rootVentral rootSympathetic trunkganglionSternum(b) Cross section of thorax showing the main roots and branches of a spinal nerve. Branches of intercostalnerve • Lateral cutaneous• Anterior cutaneousCervical PlexusFormed by ventral rami of C1–C4Innervates skin and muscles of the neck, ear, back of head, and shouldersPhrenic nerveMajor motor and sensory nerve of the diaphragm (receives fibers from C3–C5)Figure 13.8Hypoglossalnerve (XII)C1C2C3C4C5SegmentalbranchesLesser occipitalnerveGreater auricularnerveAnsa cervicalisPhrenic nerveSupraclavicularnervesAccessory nerve (XI)Transversecervical nerveVentralrami:Ventral ramiTable 13.3Brachial PlexusFormed by ventral rami of C5–C8 and T1 (and often C4 and T2) It gives rise to the nerves that innervate the upper limbMajor branches of this plexus: Roots—five ventral rami (C5–T1)Trunks—upper, middle, and lowerDivisions—anterior and posterior Cords—lateral, medial, and posterior Figure 13.9 (a)UpperMiddleTrunksLowerRoots (ventral rami):Upper subscapularLower subscapularThoracodorsalMedial cutaneousnerves of the armand forearmLong thoracicMedial pectoralLateral pectoralNerve tosubclaviusSuprascapularDorsal scapular PosteriordivisionsAnteriordivisionsLateralPosteriorCordsMedialAxillaryMusculo-cutaneousRadialMedianUlnarPosteriordivisionsTrunksRootsC4C5C6C7C8T1(a) Roots (rami C5 – T1), trunks, divisions, and cordsFigure 13.9 (d)Anteriordivisions(d) Flowchart summarizing relationships within the brachial plexus Major terminalbranches(peripheral nerves)CordsDivisionsTrunksRoots(ventralrami)MusculocutaneousMedianUlnarRadialAxillaryAnteriorPosteriorAnteriorPosteriorPosteriorAnteriorUpperMiddleLowerLateralMedialPosteriorPosteriordivisionsTrunksRootsC5C6C7C8T1Brachial Plexus: NervesAxillary—innervates the deltoid, teres minor, and skin and joint capsule of the shoulderMusculocutaneous—innervates the biceps brachii and brachialis and skin of lateral forearmMedian—innervates the skin, most flexors and pronators in the forearm, and some intrinsic muscles of the handUlnar—supplies the flexor carpi ulnaris, part of the flexor digitorum profundus, most intrinsic muscles of the hand, and skin of medial aspect of handRadial—innervates essentially all extensor muscles, supinators, and posterior skin of limbFigure 13.9 (c)Median nerveMusculocutaneous nerveRadial nerveHumerusUlnaUlnar nerveMedian nerveRadiusRadial nerve (superficial branch)Superficial branch of ulnar nerveDorsal branch of ulnar nerveDigital branch of ulnar nerveMuscular branchDigital branch(c) The major nerves of the upper limbAxillarynerve AnteriordivisionsPosteriordivisionsTrunksRootsTable 13.4Lumbar PlexusArises from L1–L4Innervates the thigh, abdominal wall, and psoas muscleFemoral nerve—innervates quadriceps and skin of anterior thigh and medial surface of legObturator nerve—passes through obturator foramen to innervate adductor musclesFigure 13.10(a) Ventral rami and major branches of the lumbar plexus IliohypogastricL1L2L3L4L5IlioinguinalGenitofemoralLateral femoralcutaneousObturatorFemoralLumbosacraltrunkLateral femoralcutaneousAnterior femoralcutaneousSaphenousObturatorIliohypogastricIlioinguinalFemoralVentral ramiVentralrami: (b) Distribution of the major nerves from the lumbar plexus to the lower limb Table 13.5Sacral PlexusArises from L4–S4Serves the buttock, lower limb, pelvic structures, and perineumSciatic nerveLongest and thickest nerve of the bodyInnervates the hamstring muscles, adductor magnus, and most muscles in the leg and footComposed of two nerves: tibial and common fibular Figure 13.11 (a)SuperiorglutealLumbosacraltrunkInferiorglutealCommonfibularTibialPosteriorfemoralcutaneousPudendalSciatic Ventral rami and major branches of the sacral plexus L4L5S1S2S3S4S5Co1Ventral ramiVentral rami:Figure 13.11 (b)Superior glutealInferior glutealCommon fibularDeep fibularSuperficial fibularPlantar branchesTibialSural (cut)Posterior femoralcutaneousPudendalSciatic(b) Distribution of the major nerves from the sacral plexus to the lower limbTable 13.6Innervation of SkinDermatome: the area of skin innervated by the cutaneous branches of a single spinal nerveAll spinal nerves except C1 participate in dermatomesMost dermatomes overlap, so destruction of a single spinal nerve will not cause complete numbnessFigure 13.12C2C3C4C5T1T2T2T3T4T5C6C8C7C7C6T6T7T8T9T10T11T12L1S2S3L1L2L3L4L5L2L3L4L5S1C5C6C8T2C5C6S1Anterior view C2C3C4C5C6C7C8C8C8C7C7T1T2T3T4T5T6T7T8T9T10T11T12L1L2L3S1(b) Posterior view L5S2S1S1S3S2S1S2S4S5L5L5L4L5L5L4C6C6C5L4L3L2L1L4Innervation of JointsHilton’s law: Any nerve serving a muscle that produces movement at a joint also innervates the joint and the skin over the joint