Motor system. Guo-Fang Tseng

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1 Motor system Guo-Fang Tseng 1

2 Lower motoneuron: ~ final common path α-motoneuron γ-motoneuron Motor Unit Size principle Muscle spindle: nuclear bag ff. nuclear chain ff. Sensory: 1) from spindle type Ia: (annulospiral endings) type II: (flower-spray endings) 2) from tendon type Ib 2

3 Spinal Reflex: sensory + motor Muscle tone γ-loop α-γ coactivation 3

4 Lower motoneurons in ventral horn (spinal cord) 4

5 Lower Motoneurons in brainstem: * * 1) SE column: * CN III, IV, VI, XII 2) SVE column: CN V, VII, IX, X, (XI) * * 5

6 Interneurons Renshaw cells: recurrent inhibition Circuits of interneurons: pattern generators Central pattern generator: spinal locomotor circuits 6

7 Spinal Reflex 1) monosynaptic knee jerk reflex (patellar reflex; stretch reflex) 2) polysynaptic: antagonistic reflex withdrawal reflex 7

8 Withdrawal reflex flexor reflex with crossed extensor reflex Muscle Tone abnormality: hypotonia hypertonia 8

9 Upper motoneurons Supraspinal descending pathways: 1) ventromedial group: balance, posture antigravity 2) lateral group: limb control 9

10 Origin of corticospinal tract Layer Vb of primary motor cortex (4, M1), premotor cortex (6, PMC) (note: PMC projects more to brainstem reticular formation) supplementary motor cortex (SMC), cingulate motor area, 1st somatosensory area (3a in particular) 10

11 pyramidal axons corona radiata internal capsule crus cerebri (middle 3/5) pyramid pyramidal decussation Corticospinal tract 11

12 Corticospinal tract Laminae V, VI, VII, VIII, (IX) 12

13 Topography at the internal capsule 13

14 CS tract: control the precision & speed of skilled movement SELECTIVE LESION: Pyramidal tract lesion: A) Babinski sign B) slightly exaggerated stretch reflexes?? C) impaired discrete movements of fingers or toes? 14

15 Corticobulbar control: 1) To CNIII, IV, VI nucl. (eye moment control) from: frontal (areas 8 & 46) & parietal eye fields brainstem gaze centers: horizontal: rostral and caudal PPRF vertical: interstitial nucl. of Cajal at the rostral end of MLF CN III, IV, VI nucl. *conjugate eye movements; frontal eye field (saccade); parietal eye field (pursuit) bilateral control; polysynaptic eye movement toward the side contralateral to the initiating cortex **Convergence (close vision): disconjugate (control center at midbrain, rostral to oculomotor nucl.) 15

16 2) To CNV, VII, IX, X, XI, CN V: ends in nearby reticular formation (bilateral The rest end in nucleus directly 16

17 Central control of CN VII (cortical input to cranial nucl.: bilateral; to caudal nucl.: contralateral) Central Seven: unilateral upper MN lesion : paralyzes only lower face of opposite side Bell s palsy: unilateral lower MN lesion (e.g., facial nerve cut) : paralyzes half the face of the same side. 17

X: deviation of uvula to cortical lesion side on phonation @ to

18 @ To nucl. ambiguus: bilateral; but uvula & soft palate are contralateral X: deviation of uvula to cortical lesion side on to hypoglossal nucleus: contralateral X: deviation of tongue to the opposite (weak) side on protrusion (genioglossus) 18

19 The location of corticobulbar and corticopontine fibers in the crus cerebri 19

20 Rubrospinal: to cervical enlargement only Ventral tegmental decussation Rubrospinal tract Termination: spinal laminae V,VI,VII proximal upper limb flexor Inputs: ipsilateral corticorubral contralateral cerebellorubral 20

21 Medial (pontine) reticulospinal (RS) tract: oral & caudal pontine reticular nucl. chiefly ipsi.; vent. funiculus; excite extensor -MN; Excitatory center; inhibition from higher centers Lateral (medullary) RS tract: gigantocellular reticular nucl. bilateral; lat. funiculus inhibit extensor -MN(?); Inhibitory center; excitation from higher centers Characteristics: rather diffuse little somatotopy posture modulate muscle tone 21

Vestibulospinal tract Lateral VS tract: lat. vest. nucl.

proximal limb extensor -MN antigravity: posture, balance

; bilaterally MLF to upper T (on -MN) head & neck

22 Vestibulospinal tract Lateral VS tract: lat. vest. nucl. ipsi., ventral funiculus VII,VIII, excite paravertebral & proximal limb extensor -MN antigravity: posture, balance Medial VS tract: med. + inf. vest. nucl.; bilaterally MLF to upper T (on -MN) head & neck movements in response to vestibular input (MLF: ascending part, vestibulo-ocular reflex) 22

23 Vestibular nuclei inputs: 1) cerebellar fastigial nucl. 2) inhibitory: cerebellar Purkinje axons (No direct cerebral cortical lat. vest. nucl. ipsi. extensor contraction & flexor Decerebellate rigidity (extensor rigidity): lesion lat. vest. nucl. rigidity abolished 23

24 Mesencephalic projections to the spinal cord a) Periventricular (periaqueductal) central pain integrate autonomic and somatomotor activities in emotional behavior b) Tectospinal tract: superior colliculus dorsal tegmental decussation cervical cord neck muscles; br. to interneurons in gaze centers conjugate eye movement Orienting reflex: visual, auditory, vestibular, somatosensory inputs eye, head & neck movements 24

25 Propriospinal (Spinospinal) a) short: limb mm. lateral b) long: axial mm. medial 25

lobe: decerebellate rigidity alpha rigidity D: decorticate

26 A: decerebration: X between SC and IC: decerebrate rigidity gamma rigidity C: X cerebellar ant. lobe: decerebellate rigidity alpha rigidity D: decorticate rigidity: decorticate posturing Decerebrate posturing Excitatory inhibitory Decorticate posturing 26

27 Lower motoneuron lesion e.g., poliomyelitis A) Flaccid paralysis B) Loss of all reflexes hyporeflexia, areflexia Syndromes C) Pronounced Partial paralysis = paresis (part of the motor innervations of a muscle is lost) D) Hypotonia: decreased muscle tone E) Fibrillation potential: contraction of isolated denervated muscle fiber fasciculation: spontaneous contraction of motor unit(s) F) Sprouting of nearby intact nerve fibers 27

28 Upper motor neuron syndromes: spastic paralysis initially weak and flaccid, eventually spastic and hypertonia A) No profound atrophy of affected muscle: slow wasting B) Increased muscle tone: spasticity exaggerated stretch reflex (hyperreflexia): pronounced in antigravity mm. Clasp-knife rigidity Clonus : repetitive, alternating contraction of flexors and extensors C) Abnormal plantar reflex: Babinski sign 28

29 Clinical Terms: Pyramidal syndrome: e.g., what happens following capsular loss of cortical outputs as well as ascending characterized by losses of voluntary movements and spasticity Extrapyramidal syndrome: basal ganglia, cerebellum, reticular formation, or vestibular disorders with abnormal spontaneous characterized by involuntary difficulties in movement initiation and control, and changes in muscle tone 29

caudate + putamen: Globus pallidus (GP): internal

30 BASAL GANGLION Caudate nucleus Lentiform nucleus: putamen globus pallidus (pallidum) Striatum: the receiving part caudate + putamen: Globus pallidus (GP): internal (medial, GPi): external (lateral, GPe) (GPi & SNpr: output part) 30

31 31

32 Ventral striatum (VS) = nucleus accumbens Ventral pallidum (VP) = substantia innominata Basal Forebrain (substantia innominata) 1) Ventral striatopallidal system 32

33 1) motor, somatosensory cortex putamen 2) associational cortex caudate 3) thalamostriatal fiber: intralaminar & midline thalamic nucl. 4) nigrostriatal fibers: SNpc (dopaminergic) dopaminergic cells in ventral tegmental area ventral striatum 5) hippo form; temporal & prefrontal ctx, BL amygdala ventral striatum Inputs SNpc 2 parts in Substantia Nigra: SNpc (pars compacta) SNpr (pars reticulata) (also pars reticularis) 33

34 Striatopallidal projections: Striatal GABAergic cells: the receiving and output neurons 1) GABA/enkephalin neurons GPe 2) GABA/substance P neurons GPi + SNpr GPe GPi SNpr 34

35 Pallidofugal projections Direct pathways: from GPi and SNpr 1) GPi VA-VLa [ premotor ctx, SMC, frontal eye field, prefrontal ctx] 2) SNpr sup. colliculus (orienting/eye movement) 3) GPi pedunculopontine nucl. (cholinergic neurons) 4)?? habenular nucl. [ limbic sys., autonomic activity] 5) vent. pallidum MD [ prefrontal ctx, ant. cingulate gyrus 35

36 Pallidofugal- Indirect pathway: (Motor cortex) GPe subthalamus GPi, SNpr 36

37 upper GPi field H2 of Forel (lenticular fasciculus) field H of Forel + ansa lenticularis (from lower GPi) thalamic fasciculus (field H1 of Forel) VA-VLa *VLp receives cbr ff 37

38 Differences in circuitry Between Basal ganglia Cerebellum 38

39 Transmitter phenotypes of basal ganglion connections Glutamatergic: a) cortical fibers to striatum b) cortical fibers to subthalamus c) thalamic fibers to cortex d) subthalamic output fibers GABAergic: strial efferents pallidal efferents 39

40 Differences in the action of GABA/subs P neurons: (direct pathway) GPi/SNpr D1 receptor: GABA/enkephalin neurons: (indirect pathway) GPe D2 receptor: inhibitory 40

41 Parkinson s Dis. loss of dopaminergic neurons in SNpc 41

42 Disinhibition: thalamic disinhibition subthalamic disinhibition Parkinson s disease Huntington s disease Hemiballismus 42

43 Direct pathway: Facilitates movement 43

44 Pyramidal syndromes: sensory and motor losses, clasp-knife rigidity Extrapyramidal syndromes: 1:Dyskinesia: unwanted superfluous movements 1a) Hypokinetic: Parkinson's dis. loss of dopaminergic neurons in SNpc: akinesia; bradykinesia, tremor at rest, cogwheel rigidity 1b) Hyperkinetic: Huntington's dis. loss of striatal GABAergic cells; hereditary chorea, athetosis, dystonia, dementia, die in years 1c) Hemiballismus: lesion of contralateral subthalamus 2. Tardive (late) dyskinesia: abnormal face & tongue movements + cogwheel rigidity long-term antipsychotic drug treatment: DR3 hypersensitivity Cerebellar lesion syndromes: ataxia, hypotonia, intention tremor (ipsilateral) *dysmetria: such as past pointing 44

45 BASAL FOREBRAIN 1) Ventral striatopallidal system hippocampal formation, basolateral amygdala, temporal & prefrontal asso. cortices & neocortex ventral striatum ventral pallidum MD (thalamus) prefrontal cortex, ant. cingulate gyrus 2) Basal nucleus of Meynert (B) cholinergic neurons; GABAergic neurons diffuse projection: to all cortical areas + thalamus 3) Extended amygdala (BST: Bed nucleus of stria terminalis) : striatal cholinergic interneurons : corticopetal cholinergic neurons 45

46 Extended amygdala cortical areas similar to ventral striatopallidal system centromedial amygdala stria terminalis Bed nucleus of Stria Terminalis (BST) neuroendocrine, autonomic, somatomotor centers in hypothalamus & brainstem (emotional behavior) Level: slightly caudal to ventral striato-pallidal system 46

47 Central autonomic control Cortical regions: Insula, frontoparietal operculum, Medial prefrontal cortex Septal area (back end of the inner part of the frontal lobe)( pleasure zone in animals; role in reward and reinforcement along with the nucleus accumbens) Hypothalamus: esp. PV & lat. hypothalamic area Extended amygdala Periaqueductal gray 47

48 Medial forebrain bundle (1) dorsal vagal nucl. (2) autonomic nucl. of spinal cord (3) LC, Raphe, NTS (4) other reticular nucl. Dorsal longitudinal fasciculus (1) dorsal vagal nucl. (2) autonomic nucl. of spinal cord (Basal forebrain) Locus coeruleus 48

Motor System I Lower motor neurons: typed according to axon diameters

Motor System I Lower motor neurons: typed according to axon diameters MOTOR UNIT: a motoneuron + supplied m.f. -motoneuron: extrafusal muscle fibers -motoneuron: intrafusal muscle fibers, control the sensitivity