神經(jīng)生物學：第六章 運動調(diào)控

1、walkruneatBrush teethPlay tennis1Motor ControlStructrueSpinal Control of movementThe somatic motor systemThe lower motor neuronExcitatin-contraction couplingSpinal control of motor unitsBrain Control of movementDescending spinal tractsThe planning of movement by the cerebral cortexThe basal gangliaT

2、he initiation o f movement by primary motor cortexThe cerebellum3IntroductionMotor ProgramsMotor system: Muscles, joints and neurons that control musclesRole: Generation of coordinated movementsParts of motor controlSpinal cord coordinated muscle contractionBrain activate motor programs in spinal co

3、rd4The Somatic Motor SystemTypes of MusclesSmooth: digestive tract, arteries, related structures; innervated by autonomic nervous system; control the blood pressure and blood flow.Striated: Cardiac (heart) and skeletal (bulk of body muscle mass); heart musule contracts rhythmically even in the absen

4、ce of any innervation. Innervated by ANS to accelerate or slow doen heart rate. Skeletal muscle is to move the bones around the joints, to move eyes, to control respiration, to control ficial expression and to produce speech.Skeletal muscles + nervous system33 somatic5Somatic motor systembonesMuscle

5、sFlexionExtensionFlexor extensor6Axial muscles: movements of the trunkProaxial muscles: move the shoulders, elbow,pelvis and kneeDistal muscles: move the hands, feet, and digits (fingers and toes) 7The lower motor neuronThe somatic muscles are innervated by the somatic motor neurons in the ventral h

6、orn of the spinal cord. They are sometimes called lower motor neurons to distinguish them from the higher-order upper motor neurons of the brain.Final common pathway: Only LMN directly command muscle contraction. 8English neurophysiologist1932 Nobel Prize for Physiology or MedicineHis contributions:

7、SynapseFinal common pathwayMotor unitProprioceptionDecerebrate rigidityNoted publications:The Integrative Action of the Nervous SystemMammalian Physiology: a Course of Practical ExercisesCharles Scott Sherrington1857-19529The segmental organization of Lower motor neuronThe segments include Cervical

8、1-8,thoracic 1-12, lumbar 1-5, sacral 1-5.Spinal sgement?123450 arm muscles10The distribution pattern of lower motor neurons in the ventral hornLMN are distributed within the ventral horn at each spinal segment in a predictable way.The cells innervating axial muscles are medial to the cells innervat

9、ing distal musclesThe cells innervating Flexors are locating at dorsal, while those innervating extensors are locating at ventral. 11Two categories of lower motor neuron Alpha motor neuronGamma motor neuron12Alpha motor neuronAlpha motor neurons directly trigger the generation of force by muscles.Mo

10、tor unitMotor neuron pool13Graded control of muscle contraction110m hurdles14Two ways for CNS to grade the muscle contractionBy varying the firing rate of motor neurons.Alpha motor neuron-Ach-neuromuscular junction-excitatory postsynaptic potential a rapid contraction and relaxation sustained contra

11、ction requires a continual action potentials, high frequency presynaptic activity causes temporal summation of the post synaptic responses. THIS summation increases the tension in the muscle fibers and smoothes the contraction.By recruiting additional synergistic motor units. The extra tension provi

12、ded by an active motor unit depends on how many muscle fibers are in the unit. Eg. In the antigravity muscles of leg, each motor unit tends to be quite large. more than 1000muscle fibers per single alpha motor neuron.1516Not all muscle is the same.17Different typeFast twitch fiber: fewer mitochondri

13、a and rely on anaerobic metabolism. They contract rapidly and powerfully, but fatigue rapidly.slow twitch fiber: a large number of mitochondria and enzymes. relatively slow to contract but can sustain contraction for a long time without fatigue. antigravity muscles of leg and in the flight muscles o

14、f birds.18Types of motor unitsFast motor units: contain rapidly fatiguing white fibers. They are bigger and have faster conducting axons. Higher firing rateSlow motor units contains slowly fatiguing red fibers. Smaller ,more slowly conducting axon. lower firing rate19Crossed-innervation experimentFa

15、st motor unitslow motor unitFast twitch fiberslow twitch fiber20Input sources12321Muscle spindleDeep within most skeletal muscles.Also called stretch receptorIs contained in a fibrous capsule.Consists of specialized muscle fibersGroup Ia axons wrap around the fibersTo detect changes in muscle length

16、 (stretchThey are specialized for body sense, to tell us about how our body is positioned and moving in space.Intrafusal muscleExtrafusal muscle2223110m/11.91s100m/9.58sEfferentAfferentGroup Ia axonThickest myelinated axonsConduct action potential rapidlyThe largest and fastestEnter spinal cord via

17、dorsal rootsBranch repeatedly and form synapses upon both interneurons and alpha motor neuronsPowerful, a single Ia axon synapses every alpha motor neuron in the pool innervating the same muscle.Question: what is the function of this sensory input?24Myotatic reflex When a muscle is pulled on, it ten

18、ds to pull back. This was first shown by sherrington. Called myotatic reflex.If you cut the dorsal root, the stretch reflex will be eliminated even though the alpha motor neuron left intact. That means sensory feedback was involved.25The knee-jerk reflex testTo test the intactness of the nerves and

19、muscles in this reflex arc26肱二頭肌反射：醫(yī)師以左手托扶病人屈曲的肘部，并將拇指置于肱二頭肌肌腱上，然后以叩診錘叩擊拇指，正常反應為肱二頭肌收縮，前臂快速屈曲。反射中樞在頸髓56節(jié)。27肱三頭肌反射 (triceps reflex) ：醫(yī)師以左手托扶病人的肘部，囑病人肘部屈曲，然后以叩診錘直接叩擊鷹嘴突上方的肱三頭肌肌腱，反應為三頭肌收縮，前臂稍伸展。反射中樞在頸髓7828 跟腱反射：方法：仰臥、髖、膝關節(jié)屈曲、下肢外旋外展位，醫(yī)生用左手托病人足掌，使足呈過伸位，然后以叩診錘叩擊跟腱。反應為腓腸肌收縮，足向跖面屈曲。 29臨床意義：深反射的減弱或消失:下運動神經(jīng)元損

20、傷，多為器質(zhì)性病變，如末梢神經(jīng)炎，神經(jīng)根炎，脊髓前角灰質(zhì)炎可使反射弧遭受損害。深反射亢進：上運動神經(jīng)元損傷3031Gamma motor neuronAlpha motor neuron innervates extrafusal muscle.Gamma motor neuron innervates intrafusal neuron.32The function of gamma motor neuronActivation of alpha motor neuron cause s the extrafusal muscle fibers to shorten.If the muscl

21、e spindle becomes slack, it is no longer report the length of the muscle.Activation of gamma motor neurons causes the poles of the spindle to contract, keeping it working.33Summary Monosynaptic myotatic reflex arc can be viewed as a feedback loop. The principles of feedback control systems are that

22、a set pioint is determined, that means the muscle length is determined. Deviation from the set point are detected by a sensor (Ia axon) and deviations are compensated for by an effector system.(alpha motor neuron)34Gamma loopGmma motor neuron-intrafusal muscle fiber-Ia afferent axon-alpha motor neur

23、on-extrafusal muscle fibersI afferent35Proprioceptive inputs from the musclesMuscle spindleGolgi tendon organ36Golgi tendon organIt monitors muscle tension or force of contractionAre located at the junction of the muscle and the tendon Are innervated by group Ib sensory axons37Compare golgi tendon o

24、rgan with muscle spindleMuscle spindle Golgi tendon organSituated in parallelIn seriesEncodes muscle length informationMuscle tension informationInnervated by IaIb axonSynapses on interneuron and alpha motor neuronSynapses on interneuron38Reverse myotatic reflexprotects the muscle from being overloa

25、ded.to regulate muscle tension within an optimal rangeImportant for fine motor acts39Spinal interneuronsSpinal interneurons receive synaptic input fromPrimary sensory axons.Descending axons from the brainCollaterals of lower motor neuron axonsInterneurons themseleves networked togetherThis allows co

26、rordinated motor programs40Inhibitory input+-Interneurons play a critical role even in the simplest reflex. Eg. Myotatic reflexReciprocal inhibation41Excitatory inputQuestion: is inhibatory interneurons involved in this process?42Crossed-extensor reflex43The generation of spinal motor program for wa

27、lkingIs it a series of commands from the upper motor neurons? NO!Is this control exerted from within the spinal cord? YES! according to the headless chickenCircuits that give rise to rhythmic motor activity a re called central pattern generators.44NMDA receptors was sufficient fto generate this loco

28、motor activity45Sten GrillnerKarolinska InstituteLampreyA possible circuit for rhythmic alternating activity46Amyotrophic lateral sclerosis -lower motor neuron diseaseALS was first described by Jean-Martin Charcot, a french neurologist.Symptoms: Muscle weakness and paralysis. All voluntary movements

29、 eg. Walking, speaking, swallowing and breathing is lost within 1-5 years.Sensation and intellect or cognition are not affectedRare, 1/20000, victims: Lou Gehrig, baseball player.Pathology: alpha motor neurons and their upper motor neurons degeneration.Cause: unknown. Oxidative damage, excitortoxici

30、ty47Brain Control of movementDescending spinal tractsThe planning of movement by the cerebral cortexThe basal gangliaThe initiation o f movement by primary motor cortexThe cerebellum48The motor control hierarchyHow does the brain influence the activity of the spinal cord to command voluntary movemen

31、ts?49Descending spinal tracts voluntary movement of distal musculatureUnder direct cortical controlPostture and locomotionUnder brain stem control?How does the brain communicate with spinal cord50The Lateral PathwaysThe Lateral PathwaysVoluntary movement - Under direct cortical controlComponentsCort

32、icospinal tract (pyramidal tract)Rubrospinal tract51.What is voluntary movement?First, voluntary movements are organized around the performance of a purposeful task. Eg. lift a glass of water, return a tennis serveSecond, the effectiveness of voluntary movements improves with experience and learning

33、. Finally,unlike reflexes, voluntary movements are not mere responses to environmental stimuli but can be generated internally52The longest neural tract2/3 originate in the motor cortex1/3 originate in the somatic sensory cortexPass through internal capsule-cerebral peduncle-pons-base of the medulla

34、, forms medullary pyramid-crosses at the junction of medulla and spinal cord,pyramidal decussation-terminate at the dorsal lateral region of ventral hornCorticospinal tractCerebral pedunclemedullaSpinal cord53Internal capsuleThe internal capsule is a white matter structure situated in the inferomedi

35、al part of eachcerebralhemisphere of brain. It carries information past the basal ganglia, separating the caudatenucleus and the thalamus from the putamen and the globus pallidus. The internal capsule contains both ascending and descending axons. The Internal Capsule contains fibres going to and com

36、ing from the cerebral cortex The corticospinaltract constitutes a large part of the internal capsule, carrying motor information from the primary motor cortex to the lower motor neurons in the spinal cord. 54strokeWhat is the symptoms of this patient? haemorrhagic stroke55Pyramidal decussationAt the

37、 junction of medulla and spinal cordThe pyramidal tract crossesThe right cortex commands the muscles on the left side, the left cortex controls the muscles on the right side.56Rubrospinal tractMuch smallerOriginate in the red nucleusDecusate in the ponsJoin in the corticalspinal tract in the lateral

38、 column of the spinal cordMajor source of input is the very region of frontal cortex that also contribute to the cortical spinal tract57The Lateral Pathways (Contd)The Effects of Corticospinal LesionsDeficit in fractionated movement of arms and handsParalysis on contralateral side Recovery if rubros

39、pinal tract intactSubsequent rubrospinal lesion reverses recovery 58The Ventromedial PathwaysOriginate in the brain stem, terminate among the spinal interneuronControl proximal and axial musclesUse sensory information about balance, body position, and the visual enviorment; Maintain balance and body

40、 Posture Four components:The Vestibulospinal tract : head balance, head turningThe Tectospinal tract: orienting responseThe Pontine Recticulospinal: Medullary Recticulospinal tract59Posture and locomotion - originates in brain stemThe Vestibulospinal tract : head balance, head turning;receive inform

41、atin from vestibular labyrinth; project bilaterally down to the spinal cordThe Tectospinal tract: orienting response;receive input from the retina and visual cortex;The Ventromedial Pathways60The Ventromedial PathwaysThe Pontine and Medullary Reticulospinal tractOriginate in the reticular formationP

42、ontine: enhances antigravity reflexesMedullary: liberates antigravity muscles from reflex61The reticular formationThe reticular formation are inter-meshed neural networks throughout the brainstem, that are involved in multiple tasks such as regulating the cardiovascular system, breathing, sleep-wake

43、cycle and filteringincoming stimuli to discriminateirrelevantbackground stimuli. 62Damage to the upper motor neuronSpinal shock: reduced muscle tone (hypotonia), areflexia and paralysis. With the loss of descending brain influence, the functions of spinal cord appear to shut down.Reflexive function

44、reappear: spasticity is characterized by a dramatic and sometimes painful increase of muscle tone. (hypertonia)Babinski sign: 63Babinski signFirstly described by the french neurologist joseph babinski in 1896.Sharply scratching the sole of the foot from the heel toward the toes causes reflexive upwa

45、rd flexion of the big toe and an outward fanning of the other toes.Normal response to this stimulus is to curl the toes downward.Normal infants also exhibit the babinski sign because their descending motor tracts have not yet matured.64Descending Spinal Tractscorticospinal tractrubrospinal tractreti

46、culospinal tract(pontine, medullary)tectospinal tractVestibulospinal tractDorsolateral region of the vental horns (motor neuron), intermediate zone (interneuron)Control distal flexorVoluntary movement of the distalmuscle.Terminate at spinal interneurons controlling axial and proximal muscles.maintai

47、n balance and body position.65Motor CortexMotor cortex is a circumscribed region of the frontal lobe.Area 4 +Area 6Demonstrated by Wilder Penfieldelectric stimulation experimentSimilar functions; different groups of muscles innervatedSMA: distal motor unitPMA: proximal motor unit through rubrospinal

48、 track“Primary motor cortex” or “M1”“Higher motor area” Lateral region Premotor area (PMA) medial region Supplementary motor area (SMA)66Somatotopic organization of precentral gyrus67The Contributions of Posterior Parietal and Prefrontal CortexAlmost all neocortex is engaged in voluntary movement co

49、ntrol.Area 5: Inputs from primary sensory cortex.Area 7: Inputs from higher-order visual cortical areas such as MT. Anterior frontal lobes: Abstract thinking, decision making and anticipating consequences of action. All the above cortex converge inputs to Area 6: convert signals encoding what action

50、s to make to how.Contribute most of the corticalspinal tracts68Area 6 (SMA，PMA) : motor planning Neurons in PMA and SMA are active before movement.The neurons play an important role in the planning of movement. 69The Basal GangliaBasal ganglia Project to the ventral lateral (VLo) nucleusProvides maj

51、or input to area 6Cortex Projects back to basal gangliaForms a “l(fā)oop”70Anatomy of The Basal GangliaDeepConsist71The Basal GangliaThe Motor Loop:Excitatory connection from cortex to putamenCortical activationExcites putamenInhibits globus pallidusRelease VLo from inhibitionActivity in VLo influences

52、activity in SMAA positive-feedback loop72The direct and indirect pathways in the basal ganglia pathway73正常情況下，黑質(zhì)到紋狀體的輸入通過激活殼核細胞增強運動環(huán)路的活動，即將VL從蒼白球的抑制中解脫出來。IndirectdirectBasal Ganglia DisordersParkinsons disease: Trouble initiating willed movements due to increased inhibition of the thalamus by basal

53、gangliaSymptoms: Bradykinesia, akinesia, rigidity and tremors of hand and jawpathology: Degeneration of dopaminergic substantia nigra inputs to striatumDopa treatment: Facilitates production of dopamine to increase SMA activitySubstantia nigra pars compacta74Parkinsons disease75IndirectdirectPD時，多巴胺耗竭關閉了通過基底神經(jīng)節(jié)和VL到SMA的輸入通路，這是導致PD運動癥狀的根本原因。Huntingtons diseaseSymptoms: Hyperkinesia, dyskinesia, dementia, impaired cognitive disability, personality disorder，chorea, flicking motionsPathology: loss of neurons in caudate, putamen, globus pallidusLoss of inhibition with loss of neuro