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    Chapter 10: Control of Body Movement

    Dr. Wei in Ren

    BME 5010

    Artificial Limb

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    Asking the right questionsHow do we move the wa we do?Why do we move the way we do?Constraints ...

    Things which limit our range of movements thus shaping them

    ...and affordancesThings which permit (or even suggest) certainmethods of movement or interaction with anobject

    Motor Control Hierarchy

    Motor commands from thebrain have been modifiedby a variety of excitatoryand inhibitory controlsystems, including

    essential feedback fromsensory afferent neurons,along with vision andbalance cues.

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    I. Highest Level (cerebral cortex)1

    the primary motor cortex (Execution)responsible for generating the neural impulsescontrolling execution of movement

    the secondary motor cortex (Selection)premotor cortex guidance of movement and controlo prox ma an run musc es o e o ysupplementary motor area planning and coordinationof complex movements.posterior parietal cortex for transforming visualinformation into motor commands

    Extensive neural networks between the major motor areas of the cerebral cortex permit fine control of movement, utilizingsensory and intentional signals to activate the appropriatemotor neurons at an appropriate level of stimulation.

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    Cerebellumcoordination of voluntary motor movement, balance, and muscle tone.

    coordination of force, extent and duration of the contractions of themuscles."learn" and store motor patterns.

    Injury to the cerebellum may result in:* impaired coordination of motor movement** impaired ability to perform rapid alternating

    movements* tremors upon intentional movement* staggering, wide based walking* tendency toward falling* weak musclesslurred speech

    Basal Ganglia (BG)= Caudate Nucleus, Putamen,Globus PallidusSuppress antagonistic or

    unwanted motor behaviorsForm a link in a circuit thatoriginates in and returns tosensorimotor cortex

    enea e sur ace o ecortex)Particularly important for (1)

    habit learning, e.g., how to drive acar, and (2) selection ofmovements.

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    Cerebellum vs. Basal GangliaThe cerebellum receives input only from the sensorimotor parts of thecor ex, w ereas e asa gang a rece ve npu rom e en recerebral cortex.The cerebellum output goes only to the premotor and motor cortex,while the basal ganglia also project to the prefrontal associationcortex.The cerebellum has direct ties with the spinal cord and the brainstem.The basal ganglia have little connection to the brainstem, and no direct

    .The cerebellum apparently modifies the output of motor systems to

    bring intention into line with performance; it acts as a comparator.It has been suggested that the cerebellum has a very large associative memory.

    Park inson s Disease

    A disorder of the central nervous s stem, which affects thebrain and spinal cord.One of the most common movement disorder, and the mostcommon symptom of Parkinsons disease is constant shaking,or tremors.Certain cells in the brain make a chemical substance calleddopamine . Dopamine carries messages that tell the body howand when to move. Parkinson's disease occurs when these

    ra n ce s e or are amage an t ere s no onger enougdopamine to carry these messages, and movement becomesmore difficult.

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    III. Local levelThe lowest level of hierarch (S inal cord )Motor neurons alpha and gamma

    descending pathwaysInterneuronsexcitatory and inhibitory

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    Examples of the categories of information modifying theproduction of motor commands from the brain.

    Descending Motor PathwaysPathwa s from brain carr in motor

    commands down to lower motor neurons

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    Corticospinal pathwaysoriginate in cerebral cortex and terminate inthe spinal cord

    contralateral or crossed, meaningt at t e e t cortex contro s t emuscles on the right side of thebody (& vice versa),

    Brainstem pathwaysoriginate in the brain stemand terminate in the spinalcord

    n uences ps a era same s emotor activity.

    Important in the control of uprightposture, balance, and walking

    Note: Overlap of function between the two pathways!!

    Descending Pathways

    n erac on ex s s e ween edescending pathwaysRedundant design means damage to onesystem may be partially compensated forby the remaining systemAll movements require continuous,coordinated interaction of both types ofpathways

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    Local control of Motor Neurons

    Afferent Input:

    -

    Motor Neurons:

    Tension-monitoring: Golgi Tendon OrganJoint receptors: Sense pressure & Position

    Alpha neuronsGamma neuronsAlpha-gamma Coactivation

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    Stretch Receptor

    Skeletal Muscle AnatomyExtrafusal fibers

    Alpha motor neurons

    Intrafusal fibersStretch receptors

    Note: contractile musclefibers are extrafusal fibersand are innervated by motorneuron

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    Muscle Spindles

    Composed of 3-10 intrafusalmuscle fibers that lackmyofilaments in their centralregions

    Regardless of the reason for a change in length, the stretched spindle in scenario (a)generates a burst of action potentials as the muscle is lengthened; in scenario (b), theshortened spindle produces fewer action potentials from the spindle.

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    Alpha-Gamma Coactivation

    Alpha motor neurons (larger andcontrol the extrafusal fibers) andGamma motor neurons (smaller andcontrol the intrafusal fibers) are

    -time to get continuous informationabout muscle length.

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    Significance of Alpha-Gamma Coactivation

    M aintains constant level of stretch inintrafusal fibers during contraction andrelaxation to provide optimal feedback.

    Tension-monitoring systemsGolgi tendon organ (GTO) receptors

    Located within tendonsContracting the muscle

    activates the Golgi tendon organs

    NOTE this reciprocal innervation is opposite that of the muscle-spindleafferents!

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    GTO activation inhibits

    Golgi tendon organ (GTO) receptors

    the agonist muscle (viarelease of glycine ontoalpha-motoneuron)

    GTO receptors functionto revent over- contraction of striated

    muscle

    8.29

    Tension Monitoring in Muscles

    Stimulation of the afferent neurons of Golgi tendonorgans activates motor neurons of antagonisticmusclesThus, inhibits motor neurons of the contractingmuscle and its synergists

    NOTE this reciprocal innervation is oppositethat of the muscle-spindle afferents!

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    Stretch Reflex

    to stretching within the muscle

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    Knee Jerk Reflex: Stretch & Reciprocal

    Inhibition Reflexes

    Monosynaptic or polysynaptic ?

    Monosynaptic vs. polysynaptic reflex

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    Flexion Reflex: Pull away from Painful Stimuli

    Leg retracts from painfulstimulus and body issupported by extending theother leg.This mechanism providesfurther input from sensoryreceptors. (e.g. a response

    withdrawal reflex).

    Key components of Reflex Arc

    Receptor12 3

    4

    Sensory neuron Integrationcenter

    5 Effector

    Motor neuron

    Stimulus

    Skin

    Spinal cord(in cross-section)

    Interneuron

    Receptor site of stimulusSensory neuron transmits the afferent impulse to the CNSIntegration center either monosynaptic or polysynaptic region withinthe CNSMotor neuron conducts efferent impulses from the integration centerto an effectorEffector muscle fiber or gland that responds to the efferent impulse

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    SUMMARY:Muscle spindle afferents monitormuscle length.Golgi tendon organs monitor muscletension.Flexion Reflex: Pull away from PainfulStimuli

    Muscle Tone

    Resistance of skeletal muscle topassive stretch

    The continuous and passivepartial contraction of themuscles . It helps maintain

    pos ure

    Due to viscoelastic properties of muscle, joints & the degree of alpha motor neuron activity

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    Muscle Tone

    Hypertonia abnormally high muscle tone due togreater than normal alpha motor neuron activity

    Due to disorders of descending pathways thatdecrease inhibitory influences on motor neurons

    H otonia abnormall low muscle tone,accompanied by weakness, atrophy, and decreasedor absent reflex responses

    Muscle Tone

    develop increased tone briefly when they arestretched a bit, followed by relaxationRigidity: continual hypertonia, resistance topassive stretch is constantOther types of hypertonia include cramps(prolonged) and spasms (brief)

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    Mode of Body MovementVoluntary onsc ous awareness an a en on s rec e

    toward the action.

    InvoluntaryReflexes

    , , - ,coughing, knee jerkgraded control by eliciting stimulus

    Movement occurs at joints!

    Control of Voluntary Movement

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    Balance is MIRACULOUS !!!

    ..Complex and Interactive

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    In physics, the center

    Center of Gravity (COG)

    of gravity (CoG) of anobject is the averagelocation of its weight.In a uniform

    ,coincides with theobject's center ofmass .

    Motor activity must be informed about the bodyscenter of gravity in order to make adjustmentsin the level of stimulation to muscles whosecontraction prevents unstable conditions (falling).

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    Characteristics of Walking (Gait Cycle)

    CyclicCyclicUniversal PatternUniversal PatternBiBi--laterally symmetriclaterally symmetricRange of S eedsRange of S eedsAdaptable to Varied SurfacesAdaptable to Varied Surfaces

    EfficientEfficient

    Gait analysis

    Gait Analysis: Techniques andRecognition of Abnormal Gait

    April 30, 2007

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    Gait analysis involves the measurement of:

    . empora pa a ve oc y, ca ence, s eplength, etc.

    2. Kinematics - the movement of the body inspace without any reference to forces.

    Gait Analysis: Techniques andRecognition of Abnormal Gait

    April 30, 2007

    . net cs - t e orces nvo ve n pro uc ngthese movements.

    4. Dynamic Electromyography - the study of muscular activity patterns during walking.

    Intrafusal muscle fibersA) are found in muscle spindles.B) are innervated by alpha motor neurons.C) generate most of the tension in a skeletal muscle.D) A and B.E) A and C.

    A

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    Draw a muscle s indle within amuscle, labeling the spindle,intrafusal and extrafusal musclefibers, stretch receptors, afferentfibers, and alpha and gammaefferent fibers.

    jerk (stimulus, receptor, afferentpathway, integrating center, efferentpathway, effector, and response).