1、1234The mental body image seems to be generated by somatosensory,proprioceptive,and visual inputs to the posterior parietal cortex(area 5,area 7)5678910SensorimotorcortexBasalgangliaCerebellumBrain stemSpinal cordInterneuron -MotorneuronMotor unit(final common pathway)Receptorsmuscle,skin,joint12345
2、vThese 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 certain motor programs for the gener
3、ation of coordinated movements vThe motor control can be divided into two parts:The spinal cords command and control of coordinated muscle contraction111213141516The motor neuron pool is all of the alpha motor neurons that innervate one muscle1730 mixed spinal nervescervical 1-8thoracic 1-12lumbar 1
4、-5sacral 1-5The ventral horn of the spinal cord contains motor neurons that innervate skeletal muscle fibersVentral roots+Dorsal root=Spinal nerve18The distribution of motor neurons in the spinal cordThe motor neurons that innervate distal and proximal musculature are found mainly in the cervical an
5、d 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 skeletal musculature in armsSegments L1-S3 have a swollen ventral horn that innervate skeletal musculature in legs1920下运动神经元的损伤表现21L
6、ou 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 w
7、ith New York Yankees,who died of ALS(amyotrophic lateral sclerosis)in 193622This 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 about m
8、uscle length2324ReceptorEffectorSpinal Motor Neuron(center)SkinMuscleJointMuscle contractionHigherCenterVoluntary movementsNociceptive stimulusStretch musclesPosture maintenance25vTwo 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
9、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2627B.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28 Muscle spindles:nConsists of specialized ske
10、letal 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 myelinated axons so t
11、hey 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 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
12、 29+30nExtrafusal fibers are innervated by alpha 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 fibe
13、rs causes a contraction of the two poles of the muscle spindle,thereby pulling on the non-contractile equatorial region and keeping the Ia afferents active31Activation of alpha motor neurons shortens the extrafusal muscle fibers.If the muscle spindle becomes slack,it goes“off the air”and no longer r
14、eports the length of the muscleActivation of gamma motor neurons contracts the poles of the spindle,keeping it“on the air”3233vGolgi 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
15、 group Ib sensory axons that are slightly smaller than the Ia axons innervating the muscle spindles34Golgi 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 I
16、a 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 fibers35The Ib afferents enter the spinal cord,branch
17、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,Golgi tendon organs a
18、re 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张反射牵张反射的特点：反射弧简单，感受器和
19、效应器在同一块肌肉363738nInhibitory 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 reflex39(A&C fibers)nExcitatory inputnFlexor reflex:u
20、sed 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 eventually excite the alpha motor neurons that control all of the flexor
21、 muscles of the affected limb(and inhibitory interneurons are also recruited to inhibit the alphas that control the extensors)+40SpinalcordIpsilateralextensorsinhibitedContralateralextensorsactivated(contract)Ipsilateralflexorsactivated(contract)ContralateralflexorsinhibitedIpsilateralknee jointclos
22、es up to remove footfrom tackContralateralknee jointopens up to support greaterweight41424344Some 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 cau
23、ses 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.K+ions leave the neuron,hyperpolarizing the membrane.The hyperpolarization allows Mg2+ions to enter and clog the NMDA cha
24、nnel,arresting the flow of Ca2+(d)As Ca2+falls,the potassium channels close,resetting the membrane for another oscillation45Walking is initiated when a steady input excites two interneurons that connect to the motor neurons controlling the flexors and extensors,respectively.The interneurons respond
25、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)4647484950Control postur
26、e and under brain stem controlContol voluntary movements of the distal musculature and under direct cortical control51(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 corticospin
27、al tract in the lateral column of 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 cortex5253The vestibulospinal and tectospinal tracts keep the h
28、ead 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 retinaRecive projections from visual cortex,as well as afferents carring somatosensory and auditory informationConstruct a map of the word around u
29、sThe 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 bilaterally down the spinal cord and activates the cervical spinal circuits that control neck and back muscles and guid head mo
30、vementRely sensory information from the vestibular labyrinth in the inner earAnother:Projects ipsilaterally as far down as the lumbar spinal cordIt helps us maintain an upright and balanced posture by facilitating extensor motor neurons of the legsStimulation at one site in this map Lead to an orien
31、ting response that directs the head and eyes to move54The pontine reticulospinal tract enhance the antigravity reflexes of the spinal cordBy facilitating the extensors of the lower limbsHelps maintain a standing posture by resisting the effects of gravityThe medullary reticulospinal tract has the opposite effect:it liberates the antigravity muscles from reflex controlActivity in both reticulospinal tracts is controlled by descending signals from the cortexControl posture of the trunk and the antigravity muscles of the limbs5556
