北大神经生物学课件7神经系统对运动的调节.ppt

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Introduction,生命在于运动,运动,是动物维系个体生存和种族繁衍的基本功能之一,1,How does a coordinated movement achieved?,2,The 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 planning a pitch,3,The lowest level,execution,Represented by the,brain stem,and,spinal cord,Is concerned with,execution,Action of the,motor neuron,and,interneuron,pools that,generate the goal-directed movement,and make any necessary adjustments of posture,The motor control hierarchy have three levels,6,Overview,脊髓,内的“,下运动神经元(,Lower neurons),”，,除了受到,脊髓内局部环路,的影响外，还受到,大脑皮层运动区,及,脑干,中许多“,上运动神经元(,Upper neurons),”,的支配和协调,基底神经节,和,小脑,则向那些,上运动神经元,提供某种感觉、认知或感性的信息，使运动更加精确和协调,7,8,Sensorimotor,cortex,Basal,ganglia,Cerebellum,Brain stem,Spinal cord,Interneuron,-,Motorneuron,Motor unit,(final common pathway),Receptors,muscle,skin,joint,1,2,3,4,5,These programs are accessed,executed,and modified by,descending commands,from the,brain,The,brains command,and control of the motor programs in the spinal cord,The motor system consists of all our,muscles,and the,neurons,that command them,The spinal cord contains certain,motor programs,for the generation of coordinated movements,The motor control can be divided into,two parts,:,The,spinal cords command,and control of coordinated muscle contraction,9,Part 1 Spinal Control of Movement,10,Introduction,“,running around like a chicken with its head cut off”,The rhythmic movements could be elicited in the hind legs of cats and dogs long after their spinal cords had been severed from the rest of the central nervous system,Charles Sherington&Graham Brown(English),The importance of,circuitry within the spinal cord,for the coordinated control of movements,11,Spinal circuitry,control of movement,12,Spinal motor neurons,Alpha motor,neuron,s,Innervate,skeletal muscle,(,extrafusal muscle,),Function,:directly command muscle contract,Gamma motor neurons,Innervate,muscle spindle,(,intrafusal muscle,),Function,:regulating the muscle spindle,Interneurons,Allows coordinated motor programs to be generated,Final common pathway,(directly command muscle contract),Compare:,Upper motor neurons,Lower motor neurons,13,The Lower Motor Neurons,Alpha motor neurons,Alpha motor neurons,are directly responsible for the generation of force by muscle,Motor unit,:,one alpha motor,neuron,and,all of the muscle fibers,it innervates collectively make up motor unit,the elementary component of motor control,Motor neuron pool,:The,collection of alpha motor neurons,that innervates,a single muscle,14,The,motor unit,is an alpha motor neuron and all of the muscle,A motor unit and motor neuron pool,The,motor neuron pool,is all of the alpha motor neurons that innervate one muscle,15,Muscle innervation by lower motor neurons,30 mixed spinal nerves,cervical 1-8,thoracic 1-12,lumbar 1-5,sacral 1-5,The ventral horn of the spinal cord contains motor neurons that innervate skeletal muscle fibers,Ventral roots+Dorsal root=Spinal nerve,16,The,cervical enlargement,of the spinal cord contains the motor neurons that innervate the,arm,musclesThe,lumbar enlargement,contains neurons that innervate the muscles of the,leg,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 cord,The motor neurons that innervate,distal and proximal,musculature are found mainly in the,cervical,and,lumbar-sacral,segments of the spinal cord,Whereas those innervating,axial,musculature are found at all levelsSegments,C3-T1,have a swollen ventral horn that innervate skeletal musculature in,arms,Segments,L1-S3,have a swollen ventral horn that innervate skeletal musculature in,legs,17,Motor neurons controlling,flexors,lie,dorsal,to those controlling,extensors,Motor neurons controlling,axial,muscles lie medial to those controlling,distal,muscles,支配,躯干,部肌肉的神经元位于脊髓前角灰质最,内侧,，由此,向外,排列的神经元则支配肢体,由近及远,分布的肌肉,The distribution of lower motor neurons in the ventral horn,18,Muscle weakness and paralysis,所支配的骨骼肌瘫痪、肌张力下降、腱反射消失(,软瘫,),肌萎缩、纤维颤动或肌束颤动,见于如,肌萎缩侧索硬化症,(,amyotrophic lateral sclerosis,ALS,)：,Selective damage to,alpha motor neurons,(degeneration),脊髓,-运动神经元的进行性溃变为主,下运动神经元的损伤表现,19,Lou Gehrig Farewell Speech:,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,who died of ALS(amyotrophic lateral sclerosis)in 1936,20,Inputs to alpha motor neurons,This input is important for the,initiation,and control of voluntary movement,This input may be,excitatory or inhibitory,and is part of the,circuitry,that generates the spinal motor programs,This input provides,feedback,about muscle length,21,SPINAL CONTROL OF MOTOR UNITS,How the activity of the motor neuron,is itself controlled?,22,Reflex,Receptor,Effector,Spinal Motor Neuron,(center),Skin,Muscle,Joint,Muscle contraction,Higher,Center,Voluntary movements,Nociceptive,stimulus,Stretch muscles,Posture maintenance,23,The myotatic reflex(stretch reflex),Two types of,myotatic,reflex,Tendon reflex and muscle tonus,A.,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,单突触反射潜伏期很短，约0.7,s,只够一次突触传递时间延搁,24,25,B.,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,26,Muscle spindles:,Consists of specialized skeletal muscle fibers,In this middle region,group,Ia,sensory axons wrap around the muscle fibers of the spindle,The spindles and their associated,Ia,axons,specialized for the detection of changes in muscle length(stretch):,proprioceptors,and,propriception,Ia,axons are the thickest,myelinated,axons so they conduct action potentials very rapidly,Ia,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 horns,Proprioception from muscle spindles,Muscle 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,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,27,+,28,Gamma motor neurons,Extrafusal,fibers,are innervated by,alpha,motor neurons,Intrafusal,fibers,receive their motor,innervation,by another type of lower motor neuron called a,gamma,motor neuron,Gamma motor neurons innervate the,intrafusal,muscle fiber at the two ends of the muscle spindle,Activation 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 active,29,The function of gamma motor neurons,Activation 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 muscle,Activation of gamma motor neurons contracts the poles of the spindle,keeping it“on the air”,30,The Gamma loop,Changing the activity of the gamma motor neurons changes the set point of the myotatic feedback loop,The Gamma loop,Gamma,motor neuron,intrafusal,muscle fiber,Ia,afferent,alpha,motor neuron,extrafusal,muscle fibers,Alpha and gamma motor neurons are,simultaneously,activated by,descending commands from the brain,31,Proprioception from Golgi tendon organs,Golgi,tendon organ,Acts like a strain gauge,it monitors muscle,tension,or the force of contraction,Located at the junction of the muscle and the tendon and are innervated by,group,Ib,sensory axons,that are slightly smaller than the,Ia,axons innervating the muscle spindles,32,Golgi 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 attachment,Muscle spindles,are arranged,parallel,to the extrafusal fibers,33,The Ib afferents enter the spinal cord,branch repeatedly,and synapse on interneurons in the ventral horn,Some of these interneurons form,inhibitory,connections,with the,alpha,motor neurons innervating the same muscle.This is the basis for the reverse myotatic reflex,Circuitry of the reverse myotatic reflex,-,Muscle spindle situated in,parallel,with the muscle fibers,Golgi tendon organs are situated in,series,Ia activity from the spindle encodes muscle,length,information,While,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,34,Significance of the reverse myotatic reflex,In extreme circumstances,this reflex arc,protects the muscle from overload,The normal function is to,regulate muscle tension within an optimal range,As muscle,tension,increases,the inhibition of the alpha motor neuron slows muscle contraction,As muscle,tension falls,the inhibition of the alpha motor neuron is reducedand muscle contraction increases,This type of proprioceptive feedback is thought to be particularly important for the,proper execution of fine motor acts,such as the manipulation of fragile objects with the hands,which require a steady but not too powerful grip,35,Spinal interneurons,Most of the input to the,alpha,motor neurons comes from,interneurons,of the spinal cord,Interneurons receive synaptic input from,primary sensory axons,descending axons from the brain,and collaterals of,lower motor neuron,axons,The interneurons are themselves,networked together,in a way that allows,coordinated motor programs,to be generated in response to their many inputs,36,Reciprocal inhibition of flexors and extensors of the same joint,+,+,+,-,Inhibitory input,Contraction of one set of muscles accompanied by the relaxation of the antagonist muscles is called,reciprocal inhibition,Reciprocal inhibition is also used by descending pathways to overcome the powerful,myotatic,reflex,37,(A,&C fibers),Excitatory input,Flexor reflex:,used to withdraw a limb from an aversive stimulus,such as the withdrawal of your foot from the thumbtack,The pain fibers entering the spinal cord branch,profusedly,and activateinterneurons,in several spinal segments.These cells eventually,excite,the,alpha motor neurons,that control all of the,flexor muscles,of the affected limb,(and,inhibitory,interneurons,are also recruited to inhibit the alphas that control the,extensors,),+,+,+,+,Circuitry of the polysynaptic flexor reflex,38,Circuitry of the crossed-extensor reflex,Spinal,cord,Ipsilateral,extensors,inhibited,Contralateral,extensors,activated,(contract),Ipsilateral,flexors,activated,(contract),Contralateral,flexors,inhibited,Ipsilateral,knee joint,closes up to,remove foot,from tack,Contralateral,knee joint,opens up to,support greater,weight,39,The generation of spinal motor programs for walking,Headless chickens;behavior,A complete transectionof a cats spinal cord at the mid-thoracic level leaves the hind limbs capable of generating coordinated walking movements,When you walk,you alternately withdraw and extend your two legs,What is the mechanism to coordinate the timing?,This could be descending commands from upper motor neurons?,No!,This control is exerted from within the spinal cord?,Yes!,40,41,Central pattern generators within the spinal cord,The circuit for the coordinated control of walking must reside within the spinal cord,In general,circuits that give rise to rhythmic motor activity are called,central pattern generators,How do neural circuits generate rhythmic patterns of activity?,The simplest pattern generators,are,single neurons,whose membrane properties endow them with,pacemaker properties,(pacemaker neurons),42,Rhythmic activity in a spinal interneuron,(,Pacemaker neuron),Some neurons respond to the activation of NMDA receptors with rhythmic depolarization,(a),In the resting state,the NMDA receptor channels and the calcium-activated potassium channels are closed,(b),Glutamate causes the NMDA receptors to open,the cell membrane to depolarize,and Ca,2+,ions to enter the cell,(c),The rise in intracellular Ca,2+,causes the Ca,2+,-activated potassium channels to open.K,+,ions leave the neuron,hyperpolarizing the membrane.The hyperpolarization allows Mg,2+,ions to enter and clog the NMDA channel,arresting the flow of Ca,2+,(d),As Ca,2+,falls,the potassium channels close,resetting the membrane for another oscillation,43,A possible circuit for rhythmic alternating activity(walking),Walking is initiated when a steady input,excites two interneurons,that connect to the motor neurons controlling,the flexors and extensors,respectively.The interneurons respond to a continuous input by generating bursts of outputs.The activities of the two interneurons alternate because,they inhibit each other via other(inhibitory)interneurons,.Thus,a burst of activity in one interneuron strongly inhibits the other,(Pacemaker neuron),(Pacemaker neuron),44,Part 2 Brain Control of Movement,45,How does the brain communicate with the motor neurons of the spinal cord?,46,Overview,来自高级中枢的,下行投射,对脑干和脊髓环路的运动控制主要影响,随意运动,和,朝向目标,的运动,发出下行投射的中枢位于,脑干,某些部位以及,大脑皮质的运动区域,脑干,内的两个主要结构,前庭核,和,网状结构,对,维持姿势,很重要,皮质主要运动区,和,次要运动区(运动前区),主要对运动进行,计划,并使运动高效率执行，皮质的这种作用是通过对,脑干,内的某些高级中枢以及,脑干、脊髓中运动神经元,和,环路中间神经元,的控制来完成的,47,The descending spinal tracts control of movement,48,The descending spinal tracts,Control,posture,and under,brain stem,control,Contol,voluntary,movements,of the distal musculature and under direct,cortical,control,49,(,Pyramidal tract),Control fine movements,of the arms and fingers,The effects of lateral pathway lesions,(in monkeys),by Donald Lawrence&Hans Kuypers,(in the late 1960s),The Lateral Pathways,X,Join in corticospinal tract in the lateral column of the spinal cord,Terminate in thedorsolateral,region of the ventral horns and,intermedial gray matter,Where motor neurons and interneurons control the,distal,muscles,particularly,flexors,Input from frontal cortex,X,50,The Ventromedial Pathways,Contain four descending tracts,the vestibulospinal tract,the tectospinal tract,the pontine reticulospinal tract,the medullary reticulospinal tract,Oringinate,in the,brain stem,Terminate,among the,spinal interneurons,Controlling proximal and axial muscles,Use sensory information about balance,body position,and the visual enviroment to reflexively,maintain balance and body posture,51,Thevestibulospinal,and,tectospinal,tracts keep the,head balance,on the shoulders as the body moves through space,and they turn the head in response to new sensory stimuli,(,midbrain),Recive direct input from,retina,Recive projections from,visual cortex,as well as afferents carring,somatosensory and au