motor_2011 - Motor Systems Nov. 9, 2011 Ralph Adolphs 1...

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Unformatted text preview: Motor Systems Nov. 9, 2011 Ralph Adolphs 1 Summary from last time Motor cortex Corticospinal tract Motor neurons Reflexes Basal ganglia Higher motor functions 2 Touch has labeled lines that originate in specialized receptors Touch has somatotopy DCML and pain pathways Discriminative and motivational aspects are dissociable Interrupt with questions if unclear Email me or visit if still unclear 3 4 Stages of Processing 1. 2. 3. 4. 5. 6. 7. Transduction Perception (early) Recognition (late perception) Memory (association) Judgment (valuation, preference) Planning (goal formation) Action 5 Examples of motor output • • • • • • • • • Spinal reflexes and motor units Posture and muscle tone Locomotion Control of distal extremities Breathing Eye movements Speech Emotions Autonomic Nervous System (visceromotor) 6 Motor output at different levels Reflexes --spinal --central Stimulus-coupled "Fixed action patterns" Emotional reactions Actions Long-term plans Stimulus decoupled 7 Frontal Eye Fields BA 8 Premotor/supplementary Motor cortex BA 6 Primary Motor Cortex BA 4 Prefrontal Cortex (Frontal Association Areas) Broca’s Area (left side) BA 44, 45 8 9 10 d of the many anglia function builds wn” effects of the ays. Any movement ertain motor commands ted and opposing m) be suppressed. tions of the direct per execution ect pathway suppresses osing movements. sis is that the basal r performing a sequence sensory cortex frontal frontal & prefrontal cortex area 4 PPC area 6 PMlat SMA VL ruber Corticospinal (lat) basal ganglia are r function. They motor cortex and act, he motor cortex. Also, ead to motor deficits. role of the basal ganglia ces. One clue to basal here are no descending ons in spinal cord or al ganglia act on hestrate the motor dorsolateral pathways basal ganglia reticular nuclei superior colliculus vestibular nuclei ventromedial pathways Spinal Cord LMNs, Interneurons, CPGs 11 12 13 anatomical layers called laminae horacic, five lumbar, and five Dorsal root ganglion VII IX IX IX IX X VIII ot An (s tero pi la no te th ra al l t am ra ic ct ) n ro eu IML IV V VI rn te In I lum n al ro II III Primary afferents in dorsal root le l co Ven tr rsa Skin c us M Do encoding pain, temperature and A , C, III, IV A , I, II Current Biology igure 1. The segmental organization of the spinal cord. rimary sensory neurons located in dorsal root ganglia project via dorsal roots onto spinal neurons largely within the dorsal horn, and lso project rostrocaudally via white matter axon tracts. The spinal cord is divided into several layers or laminae (left side of cord) aminae I–VI constitute the dorsal horn. Laminae VII–IX are in the ventral horn. Lamina IX contains the various motoneuron pools uclei) whose axons, along with sympathetic preganglionic neurons located in intermediolateral nucleus (IML), exit via ventral roots ensory information is transmitted to brain through two principal axon tracts, the dorsal column and anterolateral system. 14 • Motor unit – motoneuron and all innervated muscle fibers; variable number of fibers, depending on force required • • Alpha-motoneuron – final common pathway • • When MN fires, all muscle fibers contract Motoneuron terminals, endplates, muscle action potentials, muscle contraction Recruitment – adding muscle units to increase force of contraction 15 The Motor Unit 16 17 18 Dorsal Horn Sensory Ventral Horn Motor Ventral Root Motor 19 20 21 22 • • Force increased by recruiting motor units • Size principle – smallest motor units (and smallest force) first; then larger motor units • Muscle fibers – slow (red); fatigue resistant (intermediate); fast, fatigue (white) Motoneurons of different sizes – small MNS to small, slow motor units; large MNs to large, fast motor units 23 24 • Sensorimotor integration in absence of supraspinal input • MNs get input from sensory fibers, interneurons and descending fibers • • • Stretch reflexes Flexion-withdrawal reflex Crossed extensor reflex 25 agazine 953 1 2 3 4 5 6 7 8 9 10 11 12 13 14 lateral corticospinal rubrospinal tract dorsal corticospinal (rodent) medial reticulospinal ventral coticospinal tectospinal 13 1 vestibulospinal lateral reticulospinal 2 spino-olivary ventral spinocerebellar 10 12 spinothalamic 11 spinoreticular 9 dorsal spinocerebellar dorsal column 8 I-III 14 E IV-VI 3 C D X 7 6 5 I E F F H J 4 A B C D VIII H B IX I A IX B,C F G H B,C VII G E A I J Renshaw cells Ia reciprocal inhibitory Group I non-reciprocal inhibitory INs producing presynaptic inhibition of group I muscle afferents INs producing presynaptic inhibition of cutaneous afferents Dorsal horn group II INs Intermediate laminae group II INs INs involved in flexion/crossedextension reflexes Lamina VIII commissural INs serving crossed reflexes INs in group I excitation toextensors G Current Biology igure 3. Descending, ascending and interneuronal pathways. xons in white matter are arranged topographically into tracts that convey ascending, descending, and interneuronal signals to nd from brain and spinal cord regions. Approximate locations in white matter are shown. Some descending (yellow) and ascending athways (blue) are shown at right. Some interneuronal pathways are shown at left. Spinal neurons are labeled with the neuron pecific marker NeuN (red) to exemplify spinal cord neuron architecture. Note that there is a much greater density of neurons in the orsal horn with smaller cell diameters. any sensory, descending and nterneuronal systems, and odulatory mechanisms exist o feed convergent information o pre-selected interneuronal athways among alternatives. rain systems control movement constitute a functional unit of motor control across a joint termed the motor output stage. Another interneuron group, the group I non-reciprocal inhibitory interneuron, demonstrates the complex control of motor function patterns of coordination. Separate modular rhythmogenic elements control flexor and extensor activity across an individual joint and these modules reciprocally inhibit each other. 26 Comparable interconnections 27 • Muscle spindle – length and change of length of muscle • Golgi tendon organ – tension of muscle contraction • Sensory information distributed to spinal cord segment, dorsal column nuclei (proprioception), cerebellum 28 • Intrafusal fibers, several types, in parallel with extrafusal muscle fibers • Two types of sensory fibers – primary (Group Ia fibers) and secondary (Group II fibers) spindle afferents • • • Group Ia – change in length (dynamic) Group II – length (static) Efferent control over intrafusal fiber length – gamma-motoneurons 29 30 • Small MNs that project out ventral roots to intrafusal fibers • Activity in gamma-MNs contracts the intrafusal muscles and makes the spindle apparatus more sensitive • In turn, the group Ia and II fibers become more active • Gamma-bias impacts muscle tone 31 32 33 Damage to Motoneuron (Cell body or axon) • Loss of motor unit innervation – weakness or paralysis of muscle • Fasciculations – spontaneous contractions of muscle fibers; detected with electromyography (EMG) • Atrophy of muscles, due to loss of trophic factors from motoneuron • Hyporeflexia or areflexia 34 35 The Basal Ganglia 36 37 38 minergic neurons mpacta are lost in egenerating nigral ulate deposits of s. This is a e disease. LEFT RIGHT Motor Cortex Cortex + Corticostriate Striatum + VA-VL Motor thalamus ex t in t - - G pa lob lli us du s ion in the SN s to the direct kes away the direct pathway. p motor activity, to striatal direct pathway. opamine, activity down, and motor compounding this ilitation, ACh ibiting the f the direct ble whammy on of the excitation ing and now unput. Again, the tion reaching the r thalamus and ACh do pa Xm + ine Substantia Nigra (pars compacta) Ansa lenticularisLenticular fasciculus CST Lateral Corticospinal Tract (LCST) Parkinson’s Disease SN Dopamine cells lost Pyramidal decussation DIRECT PATHWAY Remember: direct turns UP movement + LMN Muscles Dopamine = direct pathway Dopamine excitation lost ACh inhibition unopposed LESS MOTOR ACTIVITY!!! 39 Characteristics of Basal Ganglia Diseases • Three common characteristics: – tremor and other involuntary movements – changes in posture and muscle tone – slowness of movement without paralysis • Cause either excess or diminished movement • Cognitive changes (via caudate nucleus) 40 Also, while we have emphasized the motor function of the basal ganglia, I would like you t that other behaviors are affected by similar but separate neural loops through the basal ganglia se include an oculomotor loop that plays a role in eye movement control and limbic and rontal loops that appear involved in emotion and cognitive function. As our understanding of e other loops increases, we may be able to alter the course of particular diseases. Finally, some National Board stuff. The term “basal ganglia” usually includes the caudate, men, globus pallidus, and amygdala. We use the term more loosely to refer to a group of nucle are anatomically interconnected and have important motor functions. These are the caudate, men, globus pallidus, substantia nigra, and subthalamic nuclei. The amygdala is technicall of the basal ganglia (due to its developmental origin), but functionally is part of the limbic 41 42 43 44 \ 45 46 Links between perception and action \ 47 W NEUROREPORT hy can’t you tickle yourself? Predictor Predicted sensory feedback (Corollary discharge) Efference copy Motor command Sensory discrepancy ("tickliness") Sensorimotor system Actual sensory feedback External influences (e.g. delay) Fig. 1. A model for determining the sensory consequences of a movement. An internal forward model makes predictions of the sensory feedback based on the motor command. These predictions are then 48 12. 13. 0.5 14. 15. 16. Difference in rating 0.3 0.1 17. 18. 0.1 19. 0.3 Symptoms present 0.5 0.7 Symptoms absent Normal control subjects Subject group Fig. 6. Graph showing the mean (tickly, pleasant and intense combined) perceptual rating difference between self-produced and externally pro- 20. 21. 22. 23. 24. 25. 26. 27. 49 ( J S 1 H J W P M F ( F ( S W C A C ( C 6 M 5 B ( Mirror Neurons 50 51 FDP ot tropxE FDP ot tropxE …gnitropxE 52 FDP ot tropxE FDP ot tropxE …gnitropxE 53 FDP ot tropxE FDP ot tropxE …gnitropxE 54 FDP ot tropxE FDP ot tropxE …gnitropxE 55 FDP ot tropxE FDP ot tropxE …gnitropxE 56 FDP ot tropxE FDP ot tropxE …gnitropxE ...
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