BRAIN REGULATION OF MOTOR ACTIVITY - PowerPoint Presentation

1. BRAIN REGULATION OF MOTOR ACTIVITY

2. BRAIN REGULATION OF MOTOR ACTIVITYControl of skeletal muscle activity muscle tone and movementa-motor neurons in brain stem and SCa-motor neurons are the final common pathway

3. MUSCLE TONEContinuous partial contraction of skeletal muscles in a relaxed awake animalMuscle tone is important forMaintenance of postureVenous return to heartMaintenance of body temperatureInitiation of locomotor activityAlterations in posture

4. NEURAL MECHANISMS IN MUSCLE TONEMuscle tone is lost when Dorsal or Ventral root fibers are cutBoth sensory and motor systems involvedSegmental control of muscle toneDescending tracts Change muscle toneEg: corticospinal , reticulospinal tractsCerebral motor systems Fiber systems that change muscle tone

5. MOVEMENTInvolves organized contraction of sk. muscles Propulsion of organism along the groundAlternate shifting of limbsFine degree of organization of muscle contraction Smoothness of locomotionFlexors initiate locomotion simultaneously extensors relaxForward movement of limb fine balance of phasic contraction of agonists & antagonist musclesAs the limb is placed on the ground myotatic reflexes produce a supporting column of the limb

6. MECAHNSIMS IN MOTOR ACTIVITYMotor activity involves complex interrelationships among muscles that create movement muscles that oppose (regulate the rate of movement)Those that stabilize joints for supporting the bodyPrecession of these relationships determines the smoothness of movementsMechanisms that regulate the precession are local to SCRhythmic alternation of movements in limbs could be observed in a spinal animalMechanisms for coordinating movement of all the four limbs arePartly inherent to SC Mostly regulated by higher centers

7. VOLUNTARY AND REFLEX MOTOR ACTIVITYDifficult to distinguish between the twoReflex Motor Activityinherent to SCnot apparently regulated by higher centersVoluntary Motor ActivityRequires involvement of higher centersComplex CNS pathways are involvedNo difference in voluntary or reflex motor activities elicited

8. DECEREBRATE RIGIDITYDecerebrate animalBrain stem is cut through the mid brainMuscle tone is greatly increasedStrong tonic contraction of both extensors and flexors in limbsBut extensors being more powerful, limbs remain in extensionTherefore decerebrate rigidity is also known as “exagerated reflex standing”Decrebrate rigidityNot due to irritation at the level of leisonPersists in chronic preparationRelease phenomenonCaused by withdrawal of normal descending inhibitory signals to segmental myotatic reflexes in SCCaused by loss of activation of inhibitory centers in RF of medulla controlled by cortexMuscle tone is a balance between descending inhibtory and local faciltatory influencesIf inhibitory influences are removed, the facilitatory effects are exhibited

9. CEREBRAL CONTROL OF MOTOR ACTIVITYBrain controls motor activity throughPyramidal SystemExtra Pyramidal SystemNot independent but interdependent

10. PYRAMIDAL SYSTEMComposed of only one tractCorticospinal tractOrignates in the pyramidal cells in frontal cortex Name bec. of the shape at medullaMany of the fibers terminate within the motor nuclei of brain stem before reaching the level of pyramidMany fibers are Small and unmyelinated

11. FUNCTIONS OF THE PYRAMIDAL SYSTEMGreat facilitation is required to elicit motor activity from this tractIn animals Corticospinal tract fibersterminate on interneurons in SCThat excite flexors and inhibit extensors in limbsNormal standing posture in animals is extensionThus initial movement of locomotion is flexionPyramidal tract induces the required initial flexion

12. EXTRA PYRAMIDAL SYSTEMAll motor areas other than corticospinal tractTraditionally EPS includes:Caudate NucleusPutamenGlobus PallidusSubstantia NigraRed NucleusSubthalamic NucleusThalamusRostral colliculusCerebellumReticular formation

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14. EXTRA PYRAMIDAL SYSTEMAfferent fibers received via various sensory systemsReciprocal connections to act in cohesionIntegrated activity important for Maintenance of posture and movement

15. FUNCTIONS OF SUBSTANTIA NIGRADestruction leads to muscle rigidity2. Sends inhibitory signals to a and g motor neurons in the spinal cord

16. FUNCTIONS OF SUBTHALAMIC NUCLEUSControls rhythmic alternate movements of contra lateral limbs2. Also influences globus pallidus

17. FUNCTIONS OF RED NUCLEUSA relay station for cortical control of a and g motor neurons 2. Stimulation causes activation of flexors of hind limbs and inhibition of extensors3. Inhibits both extensors and flexors in fore limbs

18. FUNCTIONS OF CAUDATE NUCLEUS, GLOBUS PALLIDUS AND PUTAMENHighest level of motor integration below cortex2. Initiate precise, synchronous and rhythmic motor activity as in a trotting horse3. Also modify motor activity initiated by the cortex

19. FUNCTIONS OF RETICULAR FORMATIONReticulo-spinal tracts alter activity of a and g motor neurons2. Reticulocortical projections alter the activity of cortex3. In association with cerebellum modifies the motor activity of pyramidal and EP systems

20. NERVOUS SYSTEMCEREBELLUM

21. CEREBELLUMConsidered silent area of brain for a long timeElectrical stimulation: no sensation or motor activityAblation: No Paralysis /Loss of functionAblation: abnormal rapid movementsEg: walking, running, talking etcVital to the control of rapid muscular activitiesCerebellum has no direct control over musclesHow then cerebellum controls muscular contractions?monitoring and making corrective adjustments in motor activities elicited by other parts of brainCerebellum has topographical representation of peripheral parts

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23. CEREBELLUM – FUNCTIONAL DESIGNReceives continuously updated information about peripheral parts regarding the instantaneous status, position, rates of movement and forces acting on peripheral partsThen cerebellum compares this instantaneous status with the intended status and Appraises the motor systems of any discrepency so that they send corrective signalsAgain cerebellum compares motor intentions with instantaneous statusThis goes on till a motor activity completed exactly as intenededThus cerebellum initiates major motor correction in real time – during the motor activityTo be able to undertake these real time corrective actions cerebellum is endowed withExtensive and rapid input system from both periphery and CNS motor areasEqually extensive and rapid out put system that feeds into motor areas

24. MOTOR AREAS IN THE CNSMOTOR SIGNALS / INTENTIONSPERIPHERAL ORGANSCEREBELLUMCORRECTION SIGNALS DESCREPENCYINSTANTANEOUS STATUSCEREBELLUM – FUNCTIONAL DESIGN

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26. FUNCTIONS OF CEREBELLUMMainly involved in controlling movementsControl of Posture and EquilibriumCerebellar Stretch ReflexControl of voluntary movementsDamping function of cerebellumCerebellar predictionControl of smooth progressionExtra motor prediction of cerebellumControl of ballistic movements

27. CONTROL OF POSTURE AND EQUILIBRIUM BY CEREBELLUMCerebellum controls movement and equilibrium in association with brain stem and spinal cordFor maintenance of equilibrium during movement rather than while standing Floculonodular lobe of cerebellum is importantVestibular apparatus is closely connected to cerebellum

28. CEREBELLAR STRETCH REFLEXAdds support to spinal cord stretch reflexSince the feed back time is considerably longer, the reflex is prolonged It is through this feed back pathway many postural adjustments of the body occur.

29. CEREBELLAR STRETCH REFLEX

30. CEREBELLAR CONTROL OF VOLUNTARY MOVEMENTSAlso known as ERROR CONTROL functionMotor cortex transmits far more signals than required during rapid movementsCerebellum assesses the rate of movement and calculates the time required to reach the intended pointThis information is fed into cortexNow the cortex transmits inhibitory signals to agonist muscles and excitatory signals to antagonist muscles at the appropriate timeThus cerebellum applies brakes to stop movement at the precise point of intention

31. DAMPING FUNCTION OF CEREBELLUMAll the body movements are essentially pendularwhen a limb is moved, momentum develops momentum must be overcome to stop the movementMomentum makes all pendular movements to overshootIf cerebellum is destroyed such overshoot occursThis is recognized by the conscious centers of cortex Cortex initiates movement in opposite direction to bring the limb back to point of intentionBut again the limb overshoots and again correction is initiatedlimb oscillates several times before reaching the intended point Intention tremor / action tremorIn an intact animalSignals from cerebellum to cortex And then from cortex to the limb Dampen the movement of limb such that overshooting does not occur

32. FUNCTIONS OF CEREBELLUM IN PREDICTIONHelps CNS to predict future position of moving parts of the bodyWithout cerebellum, this prediction is so deficient the moving parts move farther than the point of intentionThis is called dysmetriaDysmetria is pronounced in rapid than slow movements

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34. CEREBELLAR CONTROL OF SMOOTH PROGRESSIONMost important feature of normal motor function isAbility to progress smoothly from one movement to the next in an orderly successionWhen cerebellum is damaged, the organism cannot control the beginning of the next movementTherefore the succeeding movement may start too soon or too lateAs a result simple movements like walking become completely in-coordinated

35. EXTRA MOTOR PREDICTION BY CEREBELLUMCerebellum plays a role in predicting events other than motor activitiesEg; Rate of progression of auditory and visual phenomenaEg: an animal can predict from the rate of change in visual scene how rapidly it is approaching an objectCerebellum provides spatiotemporal relationships to sensory information

36. CEREBELLAR CONTROL OF BALLISTIC MOVEMENTSExtremely rapid movementsEg: eye movements towards points of interest in visual sceneIf cerebellum is damaged such movements become disorganizedBut these movements are so rapid that even the rapid input-output system between the cerebellum and cortex cannot account for them

37. NERVOUS SYSTEMHYPOTHALAMUS

38. HYPOTHALAMUSHypothalamus is sexually dimorphicBoth in structure and functionSexually dimorphic nucleus (SDN) present in preoptic areaRegulates sexual behaviour Size of SDN is 2X more in homosexual ramsIt is larger in heterosexual than gay men

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40. Afferent fibers from many tracts going to thalamus, basal ganglia and other higher centers Efferent fibers into hypothalamus originate in higher centersAFFERENTS AND EFFERENTS INTO HYPOTHALAMUS

41. Oxytocin release & water consrvBladder contr. HR & BPVasopressin releaseFeeding reflexessatietyGI stimulationBody temp., Panting, sweating, Thryotropin Vasopressin & circadian rhythmsThirst , hunger, LH, FSH, GHRHPupil dilat, Shvrng BPThirst, hunger, emotional driveFUNCTIONS OF HYPOTHALMIC NUCLEI

42. FUNCTIONS OF HYPOTHALAMUSClassified intoVegetativeEndocrineBehavioralVegetative functions include control ofCardiovascular systemBody temperatureBody waterUterine contractionsGI motility and feeding reflexesSleep and wakefulnessInduction of pubertyFunctions

43. CARDIOVASCULAR REGULATION BY HYPOTHALAMUSStimulation of posterior and lateral hypothalamus increasesarterial pressure (BP) and Heart rate (HR)Stimulation of POA has the opposite effectDecreases BP and HRThese effects are brought about by hpothalamic stimulation / inhibition of vagal fibers to heart

44. HYPOTHALAMIC REGULATION OF BODY TEMEPERATURELarge areas in the anterior hypothalamus especially the POA are involved in this functionAn increase in temperature of blood flowing through these areas induces heat dissipationConversely decrease in temperature induces heat conservationIn addition discuss hypothalamic thermostat

45. REGULATION OF BODY WATER BY HYPOTHALAMUSRegulation occurs through two separate pathsThirst mechanismUrinary excretion of waterThirst centre is in lateral hypothalamusSensitive to osmolality of surrounding ECFIf the ECF becomes hypertonic thirst is inducedIf the ECF becomes iso / hypotonic thirst is abolishedRenal excretion of water is controlled from SONSON also has osmoreceptors just like thirst centreWhen ECF becomes hypertonic, osmoreceptors send signals in posterior Pituitary to release ADHADH then increases reabsorption of water in renal DCT and CDConversely when ECF is iso- / hypotonic ADH release signals are abolishedTherefore more water is excreted in urine

46. REGULATION OF UTERINE CONTRACTIONS BY HYPOTHALAMUSStimulation of PVN causes secretion of oxytocinNormal stimuli for neurons in PVN areSucklingSexual intercourseManipulation of external genitalia Oxytocin induces Contractions ofsmooth muscles in the uterusAnd also myoepithelial cells in mammary gland

47. HYPOTHALAMIC REGULATION OF GASTRO INTESTINAL MOTILITY AND FEEDING REFLEXESHunger centreLocated in lateral hypothalamic areaDamage to this centre causes an animal to loose all interest in food to the extent of death due to starvationSatiety centreLocated in the ventromedial nucleusStimulation causes an animal to stop eating suddenlyDamage to this centre causes insatiable hungerMamillary bodies Induces feeding reflexes such as licking of lips, swallowing etc

48. REGULATION OF SLEEP AND WAKEFULNESSStimulation dorsal to MBsGreatly excites RASCauses wakefulness, alertness and excitementStimulation of anteriorhypothalmus in the septumInhibits mid brain RASInduces sleep

49. ROLE OF HYPOTHALAMUS IN INDUCTION OF PUBERTYHypothalamus in all mammals is insensitive to gonadal hormones till any animal attains right body weight and / ageAt the right body weight and / appropriate ageHypothalamus responds to gonadal hormonesStarts producing gonadotropin releasing hormone (GnRH)GnRH in turn cause release of gonadotrophic hormones from the anterior pituitaryGonadotrophins in turn induce gametogenesis and steroidogenesis in the gonads that signals onset of puberty.

50. ENDOCRINE FUNCTIONS OF HYPOTHALAMUSHypothalamic releasing factors / hormonesSecreted into hypothalmo-hypophyseal portal blood vesselsSome of them induce while others inhibit secretion of anterior pituitary hormonesThere are 9 releasing hormones / factorsEg: corticotrophin releasing hormpone (CRH), Thyrotrophin releasing hormone (TRH), GnRH etcTwo posterior pituitary hormonesADH and oxytocin are synthesized in the hypothalamus (PVN and SON)Stored and released from posterior pituitary on receiving neural signals from hypothalamus

51. BEHAVIORAL FUNCTIONS OF HYPOTHALAMUS

52. Reward centreLocated in the lateral and VMN areaStimulation causes feelings of pleasantness

53. Punishment centreLocated in periventricular structuresStimulation gives feelings of fear, terror and punishment

54. Sensory experiences which are neither rewarding nor punishing are not rememberedIf a sensory experience is accompanied by reward or punishment, the response of the animal becomes more and more intense with each repetition of the experienceThus the organism builds up strong memory traces for rewarding or punishing experiencesTherefore the reward and punishment centers in hypothalamus play important role in selecting information for learning.

55. LHALHAStimulation in the lateral hypothalamus leads toIncrease in general activity, Rage and Fighting

56. Stimulation of most medial portion of medial hypothalamus leads toFear and Punishment reaction

57. Stimulation of lateral portion of medial hypothalamus results in different behaviours depending on the region stimulated most anterior portion Sex drive (in front of POA) Area slightly posterior mainly drinking but some eating Area little farther excessive eating Most posterior area Sex drive

58. TopicPart A MarksPart B MarksTotalBody Fluids & Kidney102232Thermoregulation & Skin51823Digestion in simple stomach71825Digestion in Rumen82226Neurophysiology102030TOTAL40100140

59. NERVOUS SYSTEMTHALAMUS

60. THALAMUSConsidered greatest sensory ganglion of the brainConnects toBasal ganglia and cerebral cortex aboveBrain stem and spinal cord belowConnections are generally direct through long tractsSome indirect connections also are presentDivided into EpithalamusDorsal thalamusVentral thalamus

61. EPITHALAMUSHabenular NucleusParaventricular NucluesPretectal areaFunctions unknown

62. DORSAL THALAMUSSpecific Projection system (SPS)Place and modality specificityLateral genniculate body (LGB)Relays visual signals from optic tracts to visual cortexMedial genniculate body (MGB)Relays auditory signals from cochlear nerve to auditory cortexVentral basal complex (VBC)Relay of all somatic sensations except pain fromMedial lemniscal system (MLS)and spinothalamic tract (STT)to primary and secondary somatic cortexVia the trigeminal tractsPosterior Nuclear GroupRelay of pain signals from MLS & STT to cortex Latero ventral nucleiRelays signals from cerebellum to cortexNon-specific projection system (NSPS)Controls cortical activities of consciousnessOther nuclei of obscure functionsPulvinar, dorsomedial and posterior

63. VENTRAL THALAMUSVenterolateral genniculate bodyUnknown functionNucleus reticularisPart of NSPS

64. NERVOUS SYSTEMTHE BASAL GANGLIA

65. BASAL GANGLIAAnatomy is complex and poorly understoodFunctionally basal ganglia includeCaudate nucleusPutamenGlobus PallidusSubstantia nigraSub ThalamusMajor portions ofThalamusReticular formation andRed nucleusOperate in close association with aboveTherefore included in the motor control system of basal ganglia

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67. FUNCTIONS OF BASAL GANGLIADecortication ( Removal of cortex)All discrete movements disapperBut the animal is able to Walk, Eat, Sleep, Have sex normallyDestruction of basal gangliaOnly stereotyped movements such as extension, flexion, rotation etc, would remainFurther muscle rigidity through out the body occursStimulation of basal gangliaMuscle tone through out the body decreasedBasdal ganglia operate inhibitory influence on muscle tone throughCortexBSRF

68. FUNCTIONS OF BASAL GANGLIA IN BIRDSCortex is poorly developed in birdsTherefore basal ganglia form the highest level of motor integrationControl all voluntary movements undertaken by cortex in mammals

69. NERVOUS SYTEMTHE CEREBRAL CORTEX

70. THE CEREBRAL CORTEXLargest portion of CNSLeast understood portion alsoFunctional parts of cortex comprises of a thin layer ~ 100 billion neurons (in humans )Most of these neurons areGranular, fusiform or PyramidalArranged in six layerTopmost layer is agranular cortex –motor in functionLowermost is the granular cortex –sensory in functionLayers in between have intermediate charactersCortex functions in close association with thalamusAll the sensory pathways to cortex pass through thalamus

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73. FUNCTIONS OF SPECIFIC AREAS OF CORTEXDifferent functions are localized in specific areasSeveral of these functional areas are mappedAll areas concerned with perception of different senses are collectively called “SENSORY CORTEX”Those areas which elicit motor responses on stimulation are together called “MOTOR CORTEX”

74. PRIMARY SENSORY AREAS OF CORTEXIncludesSomatic sensory areaVisual sensory areaAuditory sensory areaGustatory cortexOlfactory sensory areaAll these areas have spatial localization of signals from peripheryEach sensory area has an association areaPrimary sensory area analyzes only simple aspects of a signalAssociation areas analyze intricate patterns of sensory signals

75. PRIMARY VS. ASSOCIATION AREASWhen primary visual area is stimulated only flashes of light are seen One would identify bright / low light and different colors of lightbut no patterns in the visual sceneVisual association area in coordination with primary visual area interprets the patterns in the visual sceneSimilarly when primary auditory cortex is stimulatedOnly sound is heard but not words or musicHowever, whether the sound is loud or low can be perceivedAuditory association area in coordination with primary auditory cortex interprets the sounds heardPrimary sensory areas cannot interpret the meaning of a sensationBut if primary sensory area is destroyed that sensory experience is completely lost even though association area is functional

76. SMOATIC SENSORY AREASArea of cortex to which somatic sensory signals are projectedLie in the anterior portions of parietal lobesTwo distinct and separate areas receive afferent fibers from the relay nuclei in thalamusCalled somatic area I and IISomatic area I appears to be more importantSomatic area I has high degree of spatial and modality specificationIn somatic area II such specification is poorNot much is known about the functions of somatic area II

77. FUNCTIONS OF SOMATIC AREA IDestruction of this area causes loss / defects in the following functions:Inability to localize discretely different sensationsCrude localization is still possibleInability to judge critical degrees of pressureInability to judge weight of objectsInability to judge shape of objectsInability to judge texture of materialInability to recognize relative orientation of different parts of the bodyLoss of knowledge and ability to recognize complex objectsLoss of contra lateral side of the bodyExamines only one side of the objects presentedKnowledge

78. GENERAL INTERPRETATIVE AREAAll sensory association areas meet in the posterior part of superior temporal lobeGENERAL INTERPRETATIVE AREA / Knowing area / tertiary association areaProvides meaning in terms of day to day life to different sensory experiencesWell developed in the dominant side of the brain

79. MOTOR CORTEXDivded intoPrimary / voluntary motor areaMotor association areaMotor supplemental areaAll these areas are somato topically organizedSpecific areas represent groups of muscles in each area of the bodyExtent of representation depends on the discreteness of movement requiredEg; vocal cords in humans represent a larger area than in animalsAfferent signal in flow from somatic cortex, thalamocortical tracts in both SPS and NSPSMotor association area is invovled in special movements such as writing, talking, knitting, sewing etc.Motor supplemental area requires very strong stimulation to elicit any motor activityFunctions not knownMay be a stand bye for motor association areas

80. NERVOUS SYSTEMLIMBIC SYSTEM

81. LIMIBIC SYSTEMLimbic system controlsEmotional behaviour and Motivational driveHypothalamus is at the centre of Limbic system surrounded by other subcortical structureSeptumParaolfactory areaAnterior nucleus of the thalamusPortions of basal gangliaThe hippocampus and The amygdalaLimbic cortex Surrounds the above subcortical structures and includesOrbitofrontal areaSubcallosal gyrusCingulate gyrusParahippoicampal gyrusThe uncusFunctions already discussedFunctions not clearly understoodMay be cerebral association area for control of behaviour

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84. HIPPOCAMPUSStimulation can cause any behavioral patterns ofPleasureRagePassionExcessive driveAny sensory input causes activation of some portion of hippocampusThen signals get distributed to other parts of limbic systemTherefore hippocampus is an additional channel through which incoming sensory signals initiate appropriate behaviourHippocampus is also involved in STM and LTMIf destroyed STM of only a few seconds duration could be establishedTherefore no learning is possible

85. AMYGDALAStimulation causes all effects of stimulation of hypothalamus such as Changes inAP, HR,GI motility DefecationMicturitionPupillary dilatation,PiloerectionSecretion of ant. pituitary hormonesAdditionally stimulation also causes different types of involuntary movements includingTonic movements such as raising headBending of bodyCircling movementsClonic rhythmic movementsMovements associated with olfaction, eating, licking, chewing and swallowingFurther stimulation of some of the amygdaloid nuclie can cause behaviours ofRagePunishmentSevere pain, fear and sexual activities