北大神經生物學課件7-1神經系統(tǒng)對運動的調節(jié)

1、2021/8/141Central Nervous System Control of MovementXING, GUOGANG(邢國剛), MD. Ph.D.北京大學 神經科學研究所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下運動神經元的損傷表現(xiàn)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 快速牽拉肌腱而發(fā)生的牽張反射Clinic application：了解脊髓不同節(jié)段的功能狀態(tài) 單突觸反射潛伏期很短，約0.7s 只夠一次突觸傳遞時間延擱2021/8/14262021/8/1427B. Muscle tonus 肌肉受到緩慢而持續(xù)的牽拉而發(fā)生的收縮 使骨骼肌能保持一定的肌肉張

11、力 意義: 維持身體的姿勢(posture)，而不表現(xiàn)明顯的動作 表現(xiàn)：extensor(伸肌)和flexor(屈肌)都發(fā)生肌緊張直立時，以伸肌緊張為主，因重力作用于關節(jié)，使關節(jié)趨向彎曲， 伸肌受到牽拉，引起肌緊張反射，肌緊張度增加以對抗關節(jié)屈曲 因重力持續(xù)作用于關節(jié)，肌緊張也就持續(xù)發(fā)生。使直立姿勢得以維持多突觸反射潛伏期較長，經過多個突觸傳遞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 是一種可感受肌肉長度變化或感受牽拉刺激的 本體感受器v梭內肌感受部裝置位于中間,收縮成分位于兩端, 梭內肌收縮時或牽拉梭外肌時, 感受裝置對牽拉敏感性增高 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當肌肉等長收縮時,腱器官傳入沖動頻率, 肌梭傳入沖動頻率不變;當肌肉等張收縮時,腱器官傳入沖動頻率不變, 肌梭傳入沖動頻率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 是張力感受器, 其傳入沖動對同一肌肉運動神經元起抑制作用肌梭是長度感受器,其傳入沖動對同一肌肉運動神經元起興奮作用當肌肉被動牽拉時, 二者傳入沖動頻率均：首先興奮肌梭發(fā)動牽張反射, 肌肉收縮,牽拉力大到一定程度, 興奮腱器官而抑制牽

21、張反射牽張反射的特點： 反射弧簡單，感受器和效應器在同一塊肌肉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