北大神经生物学课件7-1神经系统对运动的调节

1、2021/8/141Central Nervous System Control of MovementXING, GUOGANG(邢国刚), MD. Ph.D.北京大学 神经科学研究所Neuroscience Research Institute, Peking UniversityEmail address: 2021/8/1422021/8/1432021/8/144The mental body image seems to be generated by somatosensory, proprioceptive, and visual inputs to the posterior

2、 parietal cortex (area 5, area 7)2021/8/1452021/8/1462021/8/1472021/8/1482021/8/1492021/8/1410SensorimotorcortexBasalgangliaCerebellumBrain stemSpinal cordInterneuron - MotorneuronMotor unit(final common pathway)Receptorsmuscle, skin, joint12345vThese programs are accessed, executed, and modified by

3、 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 certain motor programs for the generation of coordinated movements vThe motor control can

4、 be divided into two parts:The spinal cords command and control of coordinated muscle contraction2021/8/1411Part 1 Spinal Control of Movement2021/8/14122021/8/1413Spinal circuitrySpinal circuitry control of control of movementmovement2021/8/14142021/8/14152021/8/1416The motor neuron pool is all of t

5、he alpha motor neurons that innervate one muscle2021/8/141730 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 nerve2021/8/1418The distribution of motor

6、 neurons in the spinal cordThe motor neurons that innervate distal and proximal musculature are found mainly in the cervical and lumbar-sacral segments of the spinal cordWhereas those innervating axial musculature are found at all levelsSegments C3-T1 have a swollen ventral horn that innervate skele

7、tal musculature in armsSegments L1-S3 have a swollen ventral horn that innervate skeletal musculature in legs2021/8/14192021/8/1420下运动神经元的损伤表现2021/8/1421Lou 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 m

8、an 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 19362021/8/1422This input is important for the initiation and contr

9、ol of voluntary movementThis input may be excitatory or inhibitory and is part of the circuitry that generates the spinal motor programsThis input provides feedback about muscle length2021/8/14232021/8/1424ReceptorEffectorSpinal Motor Neuron(center)SkinMuscleJointMuscle contractionHigherCenterVolunt

10、ary movementsNociceptive stimulusStretch musclesPosture maintenance2021/8/1425vTwo 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 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2021/8/14262021/8/1427B. 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

11、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2021/8/1428 Muscle spindles:nConsists of specialized skeletal muscle fibersnIn this middle region, group Ia sensory axons wrap

12、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 myelinated axons so they conduct action potentials very rapidlynIa axons enter the spina

13、l cord via the dorsal roots, branch repeatedly, and form excitatory synapses upon both interneurons and alpha motor neurons of the ventral hornsvMuscle 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 2021/8/1429+2021/8/1430nExtrafusal fibers are innervated by al

14、pha motor neuronsnIntrafusal fibers receive their motor innervation by another type of lower motor neuron called a gamma motor neuronnGamma 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 t

15、he muscle spindle, thereby pulling on the non-contractile equatorial region and keeping the Ia afferents active2021/8/1431Activation 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

16、Activation of gamma motor neurons contracts the poles of the spindle, keeping it “on the air”2021/8/14322021/8/1433vGolgi 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

17、 sensory axons that are slightly smaller than the Ia axons innervating the muscle spindles2021/8/1434Golgi 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

18、 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 attachmentMuscle spindles are arranged parallel to the extrafusal fibers2021/8/1435The Ib afferents enter the spinal

19、 cord, branch repeatedly, and synapse on interneurons in the ventral hornSome of these interneurons form inhibitory connections with the alpha motor neurons innervating the same muscle. This is the basis for the reverse myotatic reflex-Muscle spindle situated in parallel with the muscle fibers, Golg

20、i tendon organs are situated in seriesIa activity 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

21、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2021/8/14362021/8/14372021/8/1438nInhibitory inputnContraction of one set of muscles accompanied by the relaxation of the antagonist muscles is called reciprocal inhibitionnReciprocal inhibition is also used by descending pathways to overcome the powerful myotatic refl

22、ex2021/8/1439(A & C fibers)nExcitatory inputnFlexor reflex: used to withdraw a limb from an aversive stimulus, such as the withdrawal of your foot from the thumbtacknThe pain fibers entering the spinal cord branch profusedly and activate interneurons in several spinal segments. These cells event

23、ually 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)+2021/8/1440SpinalcordIpsilateralextensorsinhibitedContralateralextensorsactivated(contract)Ipsilateralfle

24、xorsactivated(contract)ContralateralflexorsinhibitedIpsilateralknee jointcloses up to remove footfrom tackContralateralknee jointopens up to support greaterweight2021/8/14412021/8/14422021/8/14432021/8/1444Some neurons respond to the activation of NMDA receptors with rhythmic depolarization(a) In th

25、e 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 Ca2+ ions to enter the cell(c) The rise in intracellular Ca2+ causes the Ca2+-activated potassium channels to open.

26、 K+ ions leave the neuron, hyperpolarizing the membrane. The hyperpolarization allows Mg2+ ions to enter and clog the NMDA channel, arresting the flow of Ca2+(d) As Ca2+ falls, the potassium channels close, resetting the membrane for another oscillation2021/8/1445Walking is initiated when a steady i

27、nput 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)

28、 interneurons. Thus, a burst of activity in one interneuron strongly inhibits the other(Pacemaker neuron)(Pacemaker neuron)2021/8/1446Part 2 Brain Control of Movement2021/8/14472021/8/14482021/8/14492021/8/1450The descending spinal tractsControl posture and under brain stem controlContol voluntary m

29、ovements of the distal musculature and under direct cortical control2021/8/1451(Pyramidal tract)Control fine movements of the arms and fingersThe effects of lateral pathway lesions(in monkeys)by Donald Lawrence & Hans Kuypers (in the late 1960s)Join in corticospinal tract in the lateral column o

30、f the spinal cordTerminate in the dorsolateral region of the ventral horns and intermedial gray matterWhere motor neurons and interneurons control the distal muscles, particularly flexorsInput from frontal cortex2021/8/14522021/8/1453The vestibulospinal and tectospinal tracts keep the head balance o

31、n the shoulders as the body moves through space , and they turn the head in response to new sensory stimuli(midbrain)Recive direct input from retinaRecive projections from visual cortex, as well as afferents carring somatosensory and auditory informationConstruct a map of the word around usThe motion of the fluid in this labyrinth, which accompanies movements of the head, activates hair cells that signal the vestibular nuclei via cranial nerve VIIIOne: Projects bi