北大神经生物学课件7-1神经系统对运动的调节.ppt

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1、Central Nervous System Control of MovementXING,GUOGANG(XING,GUOGANG(邢国刚邢国刚),),MD.Ph.D.MD.Ph.D.北京大学北京大学 神经科学研究所神经科学研究所Neuroscience Research Institute,Peking UniversityNeuroscience Research Institute,Peking University1Introductionv生命在于运动生命在于运动v运动运动是动物维系个体生存和种是动物维系个体生存和种族繁衍的基本功能之一族繁衍的基本功能之一2How does a

2、coordinated How does a coordinated movement achieved?movement achieved?3The mental body image seems to be generated by somatosensory,proprioceptive,and visual inputs to the posterior parietal cortex(area 5,area 7)A baseball pitcher A baseball pitcher planning a planning a pitchpitch4n nThe highest l

3、evel strategystrategyRepresented by the association areas of Represented by the association areas of neocortexneocortex and and basal gangliabasal ganglia of the of the forebrainforebrainIs concerned with Is concerned with strategystrategy:The The goalgoal of the movement and the movement of the mov

4、ement and the movement strategystrategy that best achieves the goal that best achieves the goalThe motor control hierarchy have three levels5n nThe middle leveltacticstacticsRepresented by the Represented by the motor cortexmotor cortex and and cerebellumcerebellumIs concerned with Is concerned with

5、 tacticstactics The The sequencessequences of muscle contractions of muscle contractions Arranged in Arranged in spacespace and and timetime Required to Required to smoothly and accuratelysmoothly and accurately achieve the achieve the strategic goalstrategic goalThe motor control hierarchy have thr

6、ee levels6n nThe lowest level executionexecution Represented by the Represented by the brain stembrain stem and and spinal cordspinal cord Is concerned with Is concerned with executionexecution Action of the Action of the motor neuronmotor neuron and and interneuron interneuron pools pools that that

7、 generate the goal-directed movementgenerate the goal-directed movement and and make any necessary adjustments of posturemake any necessary adjustments of postureThe motor control hierarchy have three levels7Overviewn n脊髓脊髓内的内的“下运动神经元下运动神经元(Lower neurons)Lower neurons)”，除了受除了受到到脊髓内局部环路脊髓内局部环路的影响外，还受

8、到的影响外，还受到大脑皮层运动大脑皮层运动区区及及脑干脑干中许多中许多“上运动神经元上运动神经元(Upper neurons)Upper neurons)”的的支配和协调支配和协调n n基底神经节基底神经节和和小脑小脑则向那些则向那些上运动神经元上运动神经元提供某种提供某种感觉、认知或感性的信息，使运动更加精确和协调感觉、认知或感性的信息，使运动更加精确和协调8 9SensorimotorcortexBasalgangliaCerebellumBrain stemSpinal cordInterneuron -MotorneuronMotor unit(final common pathway

9、)Receptorsmuscle,skin,joint12345vThese programs are accessed,executed,and modified by descending commands from the brainThe brains command and control of the motor programs in the spinal cordvThe motor system consists of all our muscles and the neurons that command themvThe spinal cord contains cert

10、ain motor programs for the generation of coordinated movements vThe motor control can be divided into two parts:The spinal cords command and control of coordinated muscle contraction10Part 1 Spinal Control of Movement11Introductionvv“running around like a chicken with its head cut running around lik

11、e a chicken with its head cut off”off”vvThe rhythmic movements could be elicited in the hind The rhythmic movements could be elicited in the hind legs of cats and dogs long after their spinal cords had legs of cats and dogs long after their spinal cords had been severed from the rest of the central

12、nervous been severed from the rest of the central nervous systemsystemCharles Charles SheringtonSherington&Graham Brown(English)&Graham Brown(English)The importance of The importance of circuitry within the spinal cordcircuitry within the spinal cord for for the coordinated control of movementsthe c

13、oordinated control of movements12Spinal circuitrySpinal circuitry control of control of movementmovement13Spinal motor neurons n nAlpha motorAlpha motor neuron neurons s Innervate Innervate skeletal muscleskeletal muscle(extrafusal muscleextrafusal muscle)FunctionFunction:directly command muscle con

14、tract:directly command muscle contractn nGamma motor neuronsGamma motor neurons Innervate Innervate muscle spindlemuscle spindle (intrafusal muscleintrafusal muscle)FunctionFunction:regulating the muscle spindle:regulating the muscle spindlen nInterneuronsInterneurons Allows coordinated motor progra

15、ms to be generatedAllows coordinated motor programs to be generated Final common pathwayFinal common pathway (directly command muscle contract)(directly command muscle contract)Compare:Compare:Upper motor neuronsUpper motor neuronsLower motor neuronsLower motor neurons14The Lower Motor Neurons Alpha

16、 motor neurons Alpha motor neuronsn nAlpha motor neuronsAlpha motor neurons are directly responsible for the are directly responsible for the generation of force by musclegeneration of force by musclen nMotor unitMotor unit:one alpha motorone alpha motor neuronneuron and and all of the all of the mu

17、scle fibersmuscle fibers it innervates collectively make up motor it innervates collectively make up motor unit,the elementary component of motor controlunit,the elementary component of motor controln nMotor neuron poolMotor neuron pool:The:The collection of alpha motor collection of alpha motor neu

18、ronsneurons that innervates that innervates a single musclea single muscle15The The motor unitmotor unit is an alpha motor is an alpha motor neuron and all of the muscleneuron and all of the muscleA motor unit and motor neuron poolThe motor neuron pool is all of the alpha motor neurons that innervat

19、e one muscle16Muscle innervation by lower motor neurons30 mixed spinal nervescervical 1-8thoracic 1-12lumbar 1-5sacral 1-5The ventral horn of the spinal cord contains motor neurons that innervate skeletal muscle fibersVentral roots+Dorsal root=Spinal nerve17The The cervical enlargementcervical enlar

20、gement of the spinal of the spinal cord contains the motor neurons that cord contains the motor neurons that innervate the innervate the armarm muscles musclesThe The lumbar enlargementlumbar enlargement contains contains neurons that innervate the muscles of neurons that innervate the muscles of th

21、e the legleg支配上肢的神经元集群位于颈膨大处，支配下肢的则在腰膨大处支配上肢的神经元集群位于颈膨大处，支配下肢的则在腰膨大处支配上肢的神经元集群位于颈膨大处，支配下肢的则在腰膨大处支配上肢的神经元集群位于颈膨大处，支配下肢的则在腰膨大处The distribution of motor neurons in the spinal cordThe motor neurons that innervate distal and proximal musculature are found mainly in the cervical and lumbar-sacral segments

22、 of the spinal cordWhereas those innervating axial musculature are found at all levelsSegments C3-T1 have a swollen ventral horn that innervate skeletal musculature in armsSegments L1-S3 have a swollen ventral horn that innervate skeletal musculature in legs18Motor neurons controlling Motor neurons

23、controlling flexorsflexors lie lie dorsaldorsal to those controlling to those controlling extensorsextensors Motor neurons controlling Motor neurons controlling axialaxial muscles lie medial to those controlling muscles lie medial to those controlling distaldistal muscles muscles支配支配躯干躯干部肌肉的神经元位于脊髓前

24、角灰质最部肌肉的神经元位于脊髓前角灰质最内侧内侧，由此，由此向外向外排列的神经元则支配肢体排列的神经元则支配肢体由近由近及远及远分布的肌肉分布的肌肉The distribution of lower motor neurons in the ventral hornThe distribution of lower motor neurons in the ventral horn19n nMuscle weakness and paralysisMuscle weakness and paralysis所支配的骨骼肌瘫痪、所支配的骨骼肌瘫痪、肌张力下降、腱反射消失肌张力下降、腱反射消失(软瘫

25、软瘫)n n肌萎缩、纤维颤动或肌束颤动肌萎缩、纤维颤动或肌束颤动n n见于如见于如肌萎缩侧索硬化症肌萎缩侧索硬化症(amyotrophic lateral amyotrophic lateral sclerosis,sclerosis,ALSALS)：Selective damage to Selective damage to alpha motor alpha motor neuronsneurons(degeneration)(degeneration)脊髓脊髓-运动神经元的进行性运动神经元的进行性溃变为主溃变为主下运动神经元的损伤表现20Lou Gehrig Farewell Spee

26、ch:Fans,for the past two weeks you have been reading about the bad break I got.Yet today I consider myself the luckiest man on the face of this earth.So I close in saying that I may have had a tough break,but I have an awful lot to live for.Lou Gehring,a star baseball player with New York Yankees,wh

27、o died of ALS(amyotrophic lateral sclerosis)in 193621Inputs to alpha motor neuronsThis input is important for the initiation and control of voluntary movementThis input may be excitatory or inhibitory and is part of the circuitry that generates the spinal motor programsThis input provides feedback a

28、bout muscle length22SPINAL CONTROL OF MOTOR UNITSHow the activity of the motor neuron is itself controlled?23ReflexReceptorEffectorSpinal Motor Neuron(center)SkinMuscleJointMuscle contractionHigherCenterVoluntary movementsNociceptive stimulusStretch musclesPosture maintenance24The myotatic reflex(st

29、retch reflex)vTwo types of myotatic reflex Tendon reflex and muscle tonusA.Tendon reflex 快速牵拉肌腱而发生的牵张反射Clinic application：了解脊髓不同节段的功能状态 reflexreflexmothedmothedCentral siteCentral siteeffecteffect肘反射肘反射扣击肱二头肌肌腱扣击肱二头肌肌腱颈颈5-75-7肘部屈曲肘部屈曲膝反射膝反射扣击股四头肌肌腱扣击股四头肌肌腱腰腰2-42-4小腿伸直小腿伸直跟腱反射跟腱反射扣击跟腱扣击跟腱腰腰5-5-骶骶2 2脚

30、向足底方向屈曲脚向足底方向屈曲单突触反射潜伏期很短，约0.7s 只够一次突触传递时间延搁25+26B.Muscle tonus 肌肉受到缓慢而持续的牵拉而发生的收缩 使骨骼肌能保持一定的肌肉张力 意义:维持身体的姿势(posture)，而不表现明显的动作 表现：extensor(伸肌)和flexor(屈肌)都发生肌紧张直立时，以伸肌紧张为主，因重力作用于关节，使关节趋向弯曲，伸肌受到牵拉，引起肌紧张反射，肌紧张度增加以对抗关节屈曲 因重力持续作用于关节，肌紧张也就持续发生。使直立姿势得以维持多突触反射潜伏期较长，经过多个突触传递27 Muscle spindles:nConsists of s

31、pecialized skeletal muscle fibersnIn this middle region,group Ia sensory axons wrap around the muscle fibers of the spindlenThe spindles and their associated Ia axons,specialized for the detection of changes in muscle length(stretch):proprioceptors and propriceptionnIa axons are the thickest myelina

32、ted axons so they conduct action potentials very rapidlynIa axons enter the spinal cord via the dorsal roots,branch repeatedly,and form excitatory synapses upon both interneurons and alpha motor neurons of the ventral hornsProprioception from Proprioception from muscle spindlesmuscle spindlesvMuscle

33、 spindle 是一种可感受肌肉长度变化或感受牵拉刺激的 本体感受器v梭内肌感受部装置位于中间,收缩成分位于两端,梭内肌收缩时或牵拉梭外肌时,感受装置对牵拉敏感性增高 28+29Gamma motor neuronsGamma motor neuronsnExtrafusal fibers are innervated by alpha motor neuronsnIntrafusal fibers receive their motor innervation by another type of lower motor neuron called a gamma motor neuron

34、nGamma motor neurons innervate the intrafusal muscle fiber at the two ends of the muscle spindle nActivation of these fibers causes a contraction of the two poles of the muscle spindle,thereby pulling on the non-contractile equatorial region and keeping the Ia afferents active30The function of gamma

35、 motor neuronsActivation of alpha motor neurons shortens the extrafusal muscle fibers.If the muscle spindle becomes slack,it goes“off the air”and no longer reports the length of the muscleActivation of gamma motor neurons contracts the poles of the spindle,keeping it“on the air”31The Gamma loopn nCh

36、anging the activity of the gamma motor Changing the activity of the gamma motor neurons changes the set point of the myotatic neurons changes the set point of the myotatic feedback loopfeedback loopn nThe Gamma loopThe Gamma loopn nGammaGamma motor neuron motor neuron intrafusalintrafusal muscle fib

37、er muscle fiber Ia Ia afferent afferent alphaalpha motor neuron motor neuron extrafusal extrafusal muscle muscle fibersfibersn nAlpha and gamma motor neurons are Alpha and gamma motor neurons are simultaneouslysimultaneously activated by activated by descending descending commands from the braincomm

38、ands from the brain32Proprioception from Golgi tendon organsvGolgi tendon organnActs like a strain gauge,it monitors muscle tension,or the force of contractionnLocated at the junction of the muscle and the tendon and are innervated by group Ib sensory axons that are slightly smaller than the Ia axon

39、s innervating the muscle spindles33Golgi tendon organs respond to increased tension on the muscle and transmit this information to the spinal cord via type Ib sensory afferents.Because the activated muscle does not change length,the Ia afferents remain silent in this example当肌肉等长收缩时,腱器官传入冲动频率,肌梭传入冲动

40、频率不变;当肌肉等张收缩时,腱器官传入冲动频率不变,肌梭传入冲动频率Golgi tendon organs lie in series between the muscle fibers and their points of attachmentMuscle spindles are arranged parallel to the extrafusal fibers34The Ib afferents enter the spinal cord,branch repeatedly,and synapse on interneurons in the ventral hornSome of

41、these interneurons form inhibitory connections with the alpha motor neurons innervating the same muscle.This is the basis for the reverse myotatic reflexCircuitry of the reverse myotatic reflex-Muscle spindle situated in parallel with the muscle fibers,Golgi tendon organs are situated in seriesIa ac

42、tivity from the spindle encodes muscle length informationWhile Ib activity from the Golgi tendon organ encodes muscle tension information腱器官 是张力感受器,其传入冲动对同一肌肉运动神经元起抑制作用肌梭是长度感受器,其传入冲动对同一肌肉运动神经元起兴奋作用当肌肉被动牵拉时,二者传入冲动频率均：首先兴奋肌梭发动牵张反射,肌肉收缩,牵拉力大到一定程度,兴奋腱器官而抑制牵张反射牵张反射的特点：反射弧简单，感受器和效应器在同一块肌肉35Significance of

43、 the reverse myotatic reflexn nIn extreme circumstances,this reflex arc In extreme circumstances,this reflex arc protects the muscle protects the muscle from overloadfrom overloadn nThe normal function is to The normal function is to regulate muscle tension within an regulate muscle tension within a

44、n optimal rangeoptimal rangeAs muscle As muscle tensiontension increasesincreases,the inhibition of the alpha motor,the inhibition of the alpha motor neuron slows muscle contractionneuron slows muscle contractionAs muscle As muscle tension fallstension falls,the inhibition of the alpha motor,the inh

45、ibition of the alpha motor neuron is reduced,and muscle contraction increasesneuron is reduced,and muscle contraction increasesn nThis type of proprioceptive feedback is thought to be particularly This type of proprioceptive feedback is thought to be particularly important for the important for the

46、proper execution of fine motor actsproper execution of fine motor acts,such as the,such as the manipulation of fragile objects with the hands,which require a manipulation of fragile objects with the hands,which require a steady but not too powerful gripsteady but not too powerful grip36Spinal intern

47、euronsn nMost of the input to the Most of the input to the alphaalpha motor neurons motor neurons comes from comes from interneuronsinterneurons of the spinal cord of the spinal cordn nInterneurons receive synaptic input from Interneurons receive synaptic input from primary primary sensory axonssens

48、ory axons,descending axons from the,descending axons from the brain,and collaterals of brain,and collaterals of lower motor neuronlower motor neuron axonsaxonsn nThe interneurons are themselves The interneurons are themselves networked networked togethertogether in a way that allows in a way that al

49、lows coordinated motor coordinated motor programsprograms to be generated in response to their to be generated in response to their many inputsmany inputs37Reciprocal inhibition of flexors and extensors of the same joint+-nInhibitory inputnContraction of one set of muscles accompanied by the relaxat

50、ion of the antagonist muscles is called reciprocal inhibitionnReciprocal inhibition is also used by descending pathways to overcome the powerful myotatic reflex38(A&C fibers)nExcitatory inputnFlexor reflex:used to withdraw a limb from an aversive stimulus,such as the withdrawal of your foot from the