lecture 7 motor processes

Lecture7

MotorProcesses

Cogs17*UCSD

ThreeTypesofMuscles

Striate(Skeletal)MuscleConnectedtoTendonstoBones

Voluntarymovements

Cardiac(Heart)MuscleHasendogenousrhythmofactivity,

modifiedbyneurons

Smooth(Organ)MuscleCansustaincontraction,

Mostlyautonomically controlled

SkeletalMuscles

Comein"AntagonisticPairs"

Foreach"FLEXOR"muscle,thatmovesbonestowardbody

Thereisacorresponding"EXTENSOR"muscle,thatmovessamebonesawayfrombody

Neuro-MuscularJunction

MotorNeurons(a orAlphaNeurons)

releaseAcytelcholineontomusclefibers

FiberrespondslikeaNeuronwould!Na+gatesopen,Na+enterscell

ChangeinpolarityopensCa++gatesCa++enterscell…

BUTinsteadofcausingreleaseofneurotransmitter,

Ca++activatesSarcomerestocontract themuscle

Zdisk

Sarcomere ContractileUnitinSkeletalMuscles

Sarcomere

Twokeyproteinsinvolved:Actinand

Myosin

Sarcomere ContractileUnitinSkeletalMuscles

MYOSIN

Cross-Bridges

WhenCa++entersmusclecells,

CrossBridgesactivated

ACTINcoil

SecuredtomuscleatZDisk

They'row' intopairsofActincoils

pullingthemclosertogether

SpinalReflexesSimpleCircuits

StretchReflex

MuscleSpindle(AProprioceptor)inmuscledetects

passivestretchofmuscle

MuscleSpindleexcites

MotorNeuronInSpinalCord

MotorNeuronstimulatessamemuscleto

contract,counterspassivestretch...asfromdoctor'shammer,

orfromshiftofweightwhilewalking

ThisistheONLYone-synapse

reflex

GolgiReflexOver-contractingmusclepullssohardontendonthatthe

GolgiTendonOrgan(aProprioceptor)

signalstheSpinalCord…

activatesanInhibitory Inter-Neuron

inSpinalCordthat…

inhibitsMotorNeuron

tooriginal muscle,reducing contraction

GolgiReflexOver-contractingmusclepullssohardontendon,thatthe

GolgiTendonOrgan(aProprioceptor)signalsSpinalCord

GolgiTendonOrganalso activatesan

Excitatory Inter-NeuroninSpinalCordthat

excitesMotorNeurontoAntagonistic muscle,increasing itscontraction,

whichdecreasesoriginal’scontraction

activatesanInhibitory Inter-Neuron

inSpinalCordthat

inhibitsMotorNeuron

tooriginal muscle,reducing contraction

PainWithdrawalReflex

Nociceptor(PainReceptor)

detectsnoxiousstimulus

NociceptorsynapsesinSpinalCordon

ExcitatoryInter-Neuron

ExcitatoryInter-Neuronexcites

MotorNeuron

MotorNeuroncontractsaflexormuscle

topullsensorawayfromnoxiousstimulus

ScratchReflex

OscillatorCircuit

ACerebellarReflex

SuchcircuitscanbereflexiveORcontrolled

(e.g.clapping)

Likethehuman"Raspberry"

(Tongue/Lipvibration)

InfantReflexes

Babkin ReflexPresspalms,fingersgrasp&mouthopens

Avestigialattempttoclingtofur

ACerebellarReflex

InfantReflexes

RootingReflexTouchcheek,headturns&infantsuckles

CanreappearinVERYdrunkadults,ifcerebellumsuppressedbyalcohol

ACerebellarReflex

Cortico-Spinal(Pyramidal)TractsForcontrolofvoluntary motion,oncontralateral sideofbody

Activatesmotorneuronstocontralateralskeletalmuscles

MostfiberscrosstoContralateral SpinalCord

inMedulla

Corticobulbar Tractforfacemovements

TrigeminalNervetoface

Arm

Face

CrossesoverinthePons

Cortico-SpinalPathwayfromMotorCortex

Ventro-MedialTracts

Primarilyforcontrolofposture,neck,shoulders&trunk,whereonesidecannot

moveseparatelyfromtheother

MakemultipleconnectionsinTectum,VestibularNucleus,ReticularFormation,

integratingwithsensory&arousalsystems

IncludescircuitsforWALKING,sincetwosidesmustbeintightcoordination

Bilateral andIpsi-Lateral

Cerebellum

Cerebellum

MNEMONIC:

Sarah the ballerinahas a hell of a cerebellum!

CerebellumForrapid,well-coordinated movements

requiringprecisetiming

Includepreprogramed(likeSaccades)andlearned-through-practicebehaviors...

...includingshiftsofAttention

Dependonreal-timeSensori-Motorfeedback

PurkinjeCell

CerebellarCircuits

~50BillioncellsinCerebellumalone!

CerebellarCircuits

PurkinjeCells(telephonepoles)

ThiscircuitcodesTIMEasDISTANCEsignalstravel

Sensory&Motorfeedback

ParallelFibers(telephonelines)

Purkinjes correspondtodifferentmusclegroups

Activityalongparalleltractsrepresenttimingofdifferentmoves

bychangesinPurkinjeoutputatdifferentplacesalongarray

DeepNuclei(sendinfoup

motorpathway)

SobrietyTestforCerebellumFunction

Smoothballisticmotionofhandtoface

Walkingastraightline,requiresbalance(integrationofvestibularinput)

CerebellumisparticularlysensitivetoAlcoholpoisoning,

impairingexecutionoftheseactions

BasalGanglia

Striatum

(Input)G.P.

(Output)

OrganizesactivityintoTASKS

A"Re-entrantSystem"thatkeepstrackofstatusof"sub-goals"

"Automates"complexsequentialprocess(e.g.driving) "Selects"what'sappropriatewhen

Pathologiesinclude(OCD)Obscessive CompulsiveDisorder,AttentionDeficitDisorders(ADD)&Parkinson'sdisease

InsufficientDOPAMINEfromSustantia Nigra (inTegmentum)

toStriatum

>>GreaterinhibitionfromGlobusPallidustomotornucleus(VLP)ofThalmus

Producestremors,difficultywithsmoothexecution,cognitivedeficits,eventuallyparalysis&death

Parkinsons'Disease

Treatedwith"L-Dopa",adopamineprecursorthatcrossesblood-brainbarrier

Butmanysideeffects,sinceDopaminesowidespread&multi-functionedinbrain

Canbecausedbyheadtrauma

Butalsotracedtoenvironmentaltoxins!

MotorCortex

MotorCortexPre-CentralGyrus

ATopological

Map

TopologicalCorticalMaps

MotorCortexPre-CentralGyrus

SomatosensoryCortexPost-CentralGyrus

AlignedwithTopologicalMapofbodysurfaceinadjacentSomatosensoryCortex

MotorHumunculus

NotethatHANDSareparticularlymagnified

evencomparedtoSomatosensorymap

Pre-MotorCortexPreparetoact;Planning

Prepareto

Speak

Broca's Area

MirrorCellSystem

"MirrorCells"respondwhensubjectsees/feelsselfperformingfamiliaract

Samecellsrespondwhensubjectseesanother performthatact

Simulationofobservedaction

IntegratedwithactivityofMirrorCellsinParietalLobe