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Types of MusclesSmooth: internal organsSkeletal/striated: voluntary muscles for body movementCardiac: heart, intermediateNeuromuscular JunctionSynapse where motor neuron axon meets a muscle fiberAcetylcholine (in skeletal muscles) excites muscles to contractAxon innervates > 1 muscle fibersEye muscles: 1 axon:3 fibersBiceps: 1 axon:100 fibersProprioceptorsReceptor that detects position or movement of a part of the bodyDetect stretch (muscle spindle) or tension (Golgi tendon organ) of a muscle  sends signals to SC  SC sends reflex signal to contract or relax the muscleMuscle SpindleParallel to muscleResponds to stretchMuscle stretches, receptor stretches…………didn’t finishGolgi Tendon OrganIn tendons, at opposite ends of musclesResponds to increase in muscle tension during a contraction  message to SC  inhibition of motor neurons (via interneurons)Vigorous contraction inhibits further contractionFlexor (withdrawal) reflexInitiated by cutaneous receptorsTonic inhibitionDescending influences coming down from brain that damp this reflex down so that only something strong or painful and activate itFull limb involvementPrimary afferents bifurcateIncludes interneuronsModified based on location of stimulusCrossed effectsInfant ReflexesGraspingSomething touches baby, they grab itBabinskiStroke the bottom of baby’s foot with a bit of force, its toes flare outRootingEdge of babies mouth is touched, they look around to look for a food sourceInhibited by cortex in adultsSequences of BehaviorCentral pattern generatorsNeural mechanisms that generate rhythmic patters of motor outputElicited by stimulus; frequency determined by spinal cord cellsFlapping wings, wet dog shake, find movement in fishSpinal cordMotor ProgramFixed sequence of movementsLearned or programmedLearned: sports, typing, piano playingProgrammed: grooming (mice), yawning (w/ stretch and inhalation/exhalation pattern), smiling, frowningAutomatic (If think about it, mess it up)Spinal cord, brainstem, cerebellumControl of Movement by CortexThe motor homunculusGives most devotion to face, hands, feetPrimary motor cortex contains upper motor neuronsAka precentral gyrus; in frontal lobeMotor control distributed over population of cellsActive even when imagining movementLeft side of cortex controls right side of bodyCorticospinal tract (why one side controls opposite side for voluntary movement)Mostly from primary motor cortexMost decussates (crosses) in medullaLateral CSTSynapses on lower motor neurons in spinal cord (ventral/anterior horn)Voluntary movementsMotor cortex to ventral (anterior) horn of spinal cordLateral CST:Terminates in Contralateral spinal cordControls distal limbsPyramidal tractWhat feeds into primary motor cortex?Supplementary motor cortexFor sequences of movementsPremotor cortexFor imitating movements (mirror neurons)Parietal, frontal, and temporal association cortices (what and where from visual, auditory, and somatosensation; perception of space in general)Another important connection: primary Somatosensory cortexBody part correlates between the two corticesFrom motor cortex to…Spinal cordVoluntary movement (CST)Central pattern generatorsModulation of reflexesBrainstemMotor cranial nervesAlso important connections with basal ganglia and cerebellumFeedback for later controlCerebellumMotor controlBalance and coordinationPostural controlLearned motor responses and skillsRapid ballistic movements that require accurate aim and timingEx- tapping a rhythm, speaking, typing, writing, athletics, music, eye movementsCognition/attentionTiming (sensory as well as movement)Organization of cerebellumInputs (indirect from spinal cord, cortex, vestibular system, etc)  cerebellar cortex  deep cerebellar nuclei  output targets (eventually including motor cortex)Basal GangliaPathways from cortex through bg, back to cortex, to inhibit or facilitate cortical activityCortex  basal ganglia and thalamusCaudate, putamen, globus pallidus, substantia nigra, subthalamic nucleusEnd of result: facilitation or suppression of cortical activityProblems with regions of basal ganglia – movement disturbances and cognitive / emotional disturbancesParkinson’s DiseaseOccurs when the dopamine producing cells that live in substantia nigra and project to striatum are destroyedNormally, dopamine in basal ganglia helps facilitate cortex, and thus movementWithout dopamine, too much inhibition of thalamus  too much inhibition of cortexRigidity, slowness (difficulty initiating movement), resting tremor, postural instabilityHuntington’s Diseasea fatal inherited disorder that causes degeneration of the caudate nucleus and putamenchromosome 4/// repeated sequences that code for glutamine…more repeats = earlier onsetcharacterized by uncontrollable jerking movements, and dementianot enough inhibition of thalamus so too much activity in cortexEndogenous RhythmsCircadian rhythms: rhythms that last about a day; humans’ last around 24.2 hoursWaking and sleepingHormone secretionUrine productionEating and drinkingSensitivity to drugsAge is important factorPeople around 20 year old most likely to go to bed late and wake up lateThis is not just learned- rates show a similar change across the lifespanOlder rats reach best performance shortly after awakening; younger (adolescent?) rats improve performance as day goes onWhy? To prepare for changes in environment before they occurSunrise/sunsetTemperature changes (day to night, and seasonal)Endogenous circannual rhythm1 year rhythm – hibernations, migrationsZeitgebera stimulus that resets the biological clockcircadian rhythms persis without light (“free running”), but light can reset themexamplestemperatureexercisenoisemealsbright lightJet LagProblem is that our endogenous rhythm doesn’t match external timeEasier to travel West (stay up later than normal and “sleep in”) than East (have to go to bed early and wake up early)Flight attendants on long trips across several time zones for more than 5 yearsSmaller than average hippocampus (adjusting to jet lag is stressful, and stress increases stress hormones and these can be toxic to the hippocampus especially)Some memory impairmentShift Work: people who work out of synch with regular sleep-wake cycleDuration of sleep depends on when go to bed (sleep less if go to bed in morning or afternoon)For those who work night shift, try to sleep during day, but it is difficultOther circadian rhythms (like temperature) do


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FSU PSB 2000 - MOVEMENT

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