Motor systems - PDF document

1 Motor systems Chris Thomson BVSc(Hons), Dip ACVIM ( Neurol ), Dip ECVN, PhD Associate Professor Neurobiology, Dept. of Vet. Med., University of Alaska, Fairbanks, Alaska. 2 Quadrupedal Motor Systems What are their functions? 1. Antigravity support 2. Postural p

latform for movement 3. Movement initiation, maintenance and termination Fig 5.3 Thomson and Hahn Motor hierarchy • Motor unit – LMN and NMJ • Reflexes • Central pattern generators (CPG) • UMN – Semiautomatic function – brainstem – Skilled/

learned function – forebrain • Motor planning centres 3 EMG study Kiwi chick 4 Neuromuscular junction Fig 1.4 Thomson and Hahn Motor unit = MN + innervated muscle cells Size determines degree of fine control Examples A B A B 5 UMN and LMN: the confusing c

ouplet Upper motor neurons (UMN) – central MN • Location: confined to brain and spinal cord – ‘ManagemenP’ – Control motor activity » Initiate, regulate, terminate – Lower motor neurons (LMN) – peripheral MN • Location – nerve cell body in C

NS, axon in PNS – ‘Workers’ – Connect to muscle of body, limb or head – Key part of the reflex – Spinal and cranial nerves » Cause muscle to contract 6 Motor systems Picture of ‘Stephie’ By Catie, aged 6 LMN also in CNN and visceral efferents (au

tonomic) 7 Reflexes • What is their physiological role in posture and locomotion? – Agonist - antagonist muscle interaction – Antigravity – Gait switch between retraction and protraction Fig 4.3 Thomson and Hahn 8 Appendicular muscle reflexes – Ag

onist - antagonist muscle interaction • Intersegmental connection propriospinal tract – Antigravity – Gait switch between retraction and protraction Fig 5.3 Thomson and Hahn 9 Axial muscle myotatic reflex Fig 5.2 Thomson and Hahn Effect on posture? http

://www.vcahospitals.com/ 10 Locomotion and reflexes Fig 9.1 Thomson and Hahn • Reflex wiring – B asis of locomotion in quadrupeds – Muscle stretch induces reflex contraction – Extensor postural thrust reflex – Crossed extension reflex – Diagonal st

epping reflex 11 Movement facilitates movement Using reflex circuits Gait initiation Movement changes sensory (proprioceptive) input motor neuron excitation • Sensory input stimulates reflex function • Same limb e.g. hip extension reflex hip flexion â

€¢ Other limbs e.g. limb flexion crossed extension, diagonal stepping • Spinal reflexes are the basis of movement • Used by central pattern generators 12 Central Programme/pattern Generators • Basic motor control for rhythmical movement – Alternating

contraction / relaxation – Locomotion, flying, scratching, breathing, chewing, micturition • CPG – Trigger neurons (midbrain) • Affect timing, amplitude and pattern • Efferents via reticular formation, reticulospinal tract to oscillator neurons – O

scillator neurons (spinal cord) • Alternating support (extensor) and swing (flexor) phase • Alternating limbs – Influence LMN http://almirah.deviantart.com/art/Moki - Run - Cycle 13 How can this dog still walk? 14 Spinal reflexes and amplification • UMN

Connection to LMN – UMN - > interneuron - > g MN (most UMN) - > stretches muscle spindle Amplification stage - > reflex a MN firing • Clinical significance 1. Few UMN required to trigger oscillator neurons in intumescence 2. AmplificaPion of signal via

ɣ moPor neurons What about Spinal Walking? Fig 5.2 Thomson and Hahn 15 16 UMN centres • Brainstem – origin of semi - automatic movements • Forebrain – skilled/learned movements Fig 4.15 Thomson and Hahn Fig 9.4 Thomson and Hahn 17 Divisions of Motor

Systems • Extrapyramidal – Most important in quadrupeds • Pyramidal – Highly important in humans Fig 8.50, Dyce, Sack and Wensing , 4 th ed. 18 Extrapyramidal System • Origin – All brain divisions • e.g. basal nuclei, red nucleus, pontine and m

edullary reticulospinal , vestibulospinal , tectospinal tracts • Multisynaptic • Ipsi - and contralateral projection • Termination – a and g MN brainstem and spinal cord 19 Extrapyramidal System • Function – Posture and locomotion – Synapses pri

marily onto g - MN – Inhibitory • Medullary reticulospinal tract – Loss - > UMN spasticity – Excitatory • Extensor muscle facilitation – Vestibulospinal , tectospinal , pontine reticulospinal tracts • Flexor muscle facilitation – Rubrospina

l tract Fig 4.2 Thomson and Hahn Extensor spasticity after TL lesion 20 Spinal cord motor tracts Fig 4 - 5 Thomson and Hahn ID Name A Propriospinal ( spino - spinal) H Rubrospinal I Lateral corticospinal J Lateral tectotegmentospinal K Medullary (lateral) retic

ulospinal L Pontine (ventral) reticulospinal M Lateral vestibulospinal N Tectospinal O Ventral corticospinal P Medial vestibulospinal and medial longitudinal fasciculus 21 Extrapyramidal Tract Function • Rubrospinal • Important in dogs and cats • Semiskill

ed and postural (flexor) activity • Reticulospinal – Medullary • Suppresses antigravity muscle activity – Pontine • Standing posture http://www.releasethehounds.com/media 22 Extrapyramidal Tract Function • Vestibulospinal tracts (VST) • Lateral V

ST – From lateral vestibular nuclei (VN) – Stimulated by static head position – Ipsilateral antigravity muscles whole body • Medial VST – From medial, rostral and caudal VN – Stimulated by head acceleration – Output to neck/shoulder muscles » Mainta

ins head posture • Medial longitudinal fasciculus – Medial VN (and other brainstem nuclei) – VF – neck and cranial thoracic cord – Brainstem to CN III, IV, VI nuclei – Coordination eye, neck and TL posture during head movement Fig 8.5 Thomson and Hah

n 23 Extrapyramidal Tract Function • Tectospinal tracts – Lateral ( tectotegmentospinal ) • UMN for sympathetic output to eyes – To T1/T2 spinal cord segments • Active pupillary dilation in response to dim light – Medial • From the corpora quadri

gemina – Rostral and caudal colliculi • Function – head/neck movement in response visual/auditory stimuli » ‘Visual grasp’, ‘audiPory grasp’ https://s - media - cache - ak0 24 Thomson and Hahn Fig A7 Corpora quadrigemina • Rostral colliculus •

Caudal colliculus 25 Extrapyramidal system • Red lines are facilitatory • Black lines are inhibitory • NOTE: vestibulospinal tract is facilitatory to ipsilateral side Fig. 13.2 King 26 Why do we get spasticity with of UMN spinal cord lesions? 27 Pyra

midal Motor System • Mammals only – Output from motor cortex: – Via crus cerebri (A) – longitudinal fibres of the pons (B) • Corticopontine – To cerebellum and back to motor cortex • Corticonuclear – e.g. to CNN nuclei of brainstem • Corticos

pinal tract, – via medullary pyramids (C,D), to spinal cord – Tracts decussate – Spinal cord • 75% decussate at C1 - 2 into lateral funiculus (LF) • rest in VF, decussate just b/4 termination Fig A3 Thomson and Hahn Dog brain, ventral aspect A A B C

D D C B 28 Motor cortex output • Function – Skilled /learned movement • Humans/primates – 30% spinal cord WM • Quadrupeds – Dogs 10% spinal cord WM – c/w ungulates – Note » horses, camelids » raccoons http://www.horsenation.com/ Fig 8.50, Dyce

, Sack and Wensing , 4 th ed. 29 Pyramidal Motor System – Clinical significance of pyramidal lesions • Humans vs quadrupeds Human Pons XS: 30 years post - stroke Where is the Lesion ? Ovine pons, Thomson and Hahn Fig A30 Fig 8.50, Dyce, Sack and Wensin

g , 4 th ed. 30 31 32 Why the difference with a forebrain lesion? http://graphics8.nytimes.com Fig 4 - 10, Thomson and Hahn 33 Fig 8 - 14 deLahunta and Glass 34 Basal nuclei - components Note red = grey matter, blue = white matter. A. Caudate nucleus B. Globus

pallidus C. Internal capsule D. Putamen E. External capsule F. Claustrum G. Extreme capsule Corpus striatum = basal nuclei and intervening WM C E F Basal nuclei – function • Humans – disease affecting BN? • Feedback circuits – modify motor output â

€“ Ritual movements? • ‘Ordering Phe componenP parPs of complex movemenP’ (Jenkins) – Lesions • putamen – propulsive activity • globus pallidus – hypoactive • caudate n. – athetoid movements • Effect of unilateral lesion? Forebrain neopl

asia Photo courtesy Kate Hill WhaP’s Phis dog’s presenPing sign? 36 Neuro RAT R eflexes A trophy T one Differentiating disease in UMN versus LMN Fig 5.6 Thomson and Hahn Sign UMN – central MN dz (damaged UMN) LMN – peripheral MN dz (damaged LMN) Re

flexes Intact (increased) Decreased/absent Atrophy Disuse: mild generalised Neurogenic: severe, specific muscles Tone Intact (increased) Decreased/absent 37 UMN lesions • Clinical effect of UMN lesions – Depends on lesion location • Rigidity/ spasticity â€

“ Loss of inhibitory input » From forebrain – decerebrate rigidity » From medullary reticular formation – limb and trunk hypertonus • Paresis /paralysis – Loss of movement initiation – Decreased facilitation LMN – Loss of skilled motor activity/co

ntrol » Motor cortex (visual placing is a good test) • Postural abnormalities – Decerebrate rigidity – mesencephalic lesion – Pleurothotonus – mesencephalic lesion – Decerebellate rigidity – rostral cerebellum – Head tilt – vestibular dysfunc

tion – Torticollis – forebrain or neck LMN (hyper or hypoactivity ) – Schiff - Sherrington – acute thoracolumbar lesion Fig 9.6 Thomson and Hahn LMN lesions • ↓ / 0 Reflexes • neurogenic atrophy • ↓ / 0 tone 38 Henry 7 yo MN Corgi, Hx 1 mo

progressive RPL lameness 39 C oordination of movement Cerebellar Function – To coordinate posture and movement • Receives input information about – Position and movement of body parts » Spinocerebellar » Vestibulocerebellar tracts – Planned motor activit

y » Forebrain » Extrapyramidal system • Send output to – Brainstem UMN centres – Forebrain » motor planning centres Cerebellar function • Continual input from – Muscles and joints (SCP) – head, neck, trunk, limbs, tail – Vestibular system –

head position – Motor planning centres • Modifies output from UMN centres – Forebrain (skilled) and brainstem (semi - automatic) – C oordinate agonist - antagonist muscle function – At rest and during locomotion • Sets the postural platform – O

n which motor activity can occur 42 Functional connections of the cerebellum Cerebellar afferents : • Proprioceptive information from trunk, limbs and head • Motor planning • Motor cortex (voluntary) – via cortiocpontocerebellar • Extrapyramidal from

forebrain and midbrain, via olivary nucleus • Cerebellar efferents • Brainstem UMN nuclei • Forebrain motor centres Postural platform Fig 7.9 Thomson and Hahn • Planned motor activity – Inform cerebellum – Cerebellum checks body posture (SCP) – Ce

rebellar efferents to UMN centres sets postural platform (UMN coordination) – New SCP to cerebellum – Cerebellum informs motor cortex – Motor activity occurs • Cerebellar dysfunction Postural paralysis Cerebellar peduncles • Rostral CP – Afferent

• ventral spinocerebellar tract – Efferent • cerebellar nuclei to midbrain and forebrain UMN centres • Middle CP – Afferent only • corticopontocerebellar tract • Caudal CP – ( restiform and juxtarestiform bodies) – Afferent • Spinocerebell

ar (dorsal, cranial, cuneocerebllar ), • vestibulocerebellar , • olivocerebellar , • reticulocerebellar (pontine and medullary) – Efferent • Cerebellovestibular • Cerebelloreticular 44 Evans, 18 - 4 and 18 - 41 Cerebellar peduncles – b ilaterall

y paired Name for their position of attachment to the brainstem • Rostral – 12 (upper image ); 6 – lower image • Middle 10 • Caudal 11; 3 Sequential images Lateral aperture Caudal and rostral CP (?) Rostral CP Middle CP (?) Caudal CP (?) Pontine nu

clei Transverse fibres of the pons 46 Cerebellar Efferents Purkinje (pyramidal) cells – May be stimulated or inhibited – They are inhibitory • t o vestibular nuclei – direct inhibition • to excitatory cerebellar nuclei – Decrease their facilitati

on of motor activity – indirect inhibition – Lateral cerebellar nucleus » To forebrain – Interposital nucleus » To red nucleus and reticular formation – Fastigial nucleus » To vestibular nucleus and reticular formation Fig 7.6c Thomson and Hahn http:

//image.slidesharecdn.com/ histologyofnervesystem Lateral CN Fastigial CN Interposital CN 47 48 Locomotion Summary • Spinal reflexes and CPG – Foundation of movement • Supraspinal input – Initiates – Terminates – C oordinates – Modulates spinal refle