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Neuromuscular integration. Tom Burkholder [email protected] 4-1029 Weber 123 http://www.ap.gatech.edu/burkholder/8813 /. Technical Frog anatomy Muscle mechanics Force transducer Feedback control. Conceptual Muscle physiology Proprioceptors Sensorimotor integration.

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Neuromuscular integration

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Neuromuscular integration l.jpg

Neuromuscular integration

Tom Burkholder

[email protected]

4-1029

Weber 123

http://www.ap.gatech.edu/burkholder/8813/


Learning goals l.jpg

Technical

Frog anatomy

Muscle mechanics

Force transducer

Feedback control

Conceptual

Muscle physiology

Proprioceptors

Sensorimotor integration

Learning goals

Develop a closed loop hybrid system to investigate some aspect of neuromuscular control. Ideally, the structure or parameters of the computational system will test a model of biological control


References l.jpg

References

  • Gasser HS and Hill AV. The dynamics of muscular contraction. Proc R Soc Lond (B) 96: 398-437, 1924.

  • Rack PM and Westbury DR. The effects of length and stimulus rate on tension in the isometric cat soleus muscle. J Physiol (Lond) 204: 443-460, 1969.

  • Nichols TR and Houk JC. Improvement in linearity and regulation of stiffness that results from actions of stretch reflex. J Neurophysiol 39: 119-142, 1976.

  • McCrea DA. Spinal circuitry of sensorimotor control of locomotion. J Physiol 533: 41-50, 2001.

  • Lutz GJ and Rome LC. Built for jumping: the design of the frog muscular system. Science 263: 370-372, 1994.

  • Rome LC, Swank D, and Corda D. How fish power swimming. Science 261: 340-343, 1993.

  • Chizeck HJ, Crago PE, and Kofman LS. Robust closed-loop control of isometric muscle force using pulsewidth modulation. IEEE Trans Biomed Eng 35: 510-517, 1988.


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Control of Motion

  • Phylogenic background

  • Motor proteins

  • Muscle properties

  • Control systems


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Protista motility

  • RNA Polymerase

  • Mitosis

  • Swimming

    • Flagella

    • Cilia

  • Crawling

    • Rolling

    • Pseudopod formation

      • Chemotactic

      • Receptor mediated activation of myosin


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Nematodes

  • Large scale swimming

    • Cyclical

    • Force/motion phase

  • Specialized organs

    • Sensors

    • Motors

    • Wiring

  • Complex behavior

    • Avoidance

Muscle activation

Muscle activation


Insect flight l.jpg

Active force

Passive force

Stimulation

Applied length

Insect Flight

  • Indirect flight muscles

    • Activated less than once per cycle

  • Molecular kinetics

    • Springlike, but positive work

    • Stretch activation


  • Mammalian locomotion l.jpg

    Mammalian locomotion

    • Multiple limbs

    • Ballistic


    Muscular work during gait l.jpg

    Muscular work during gait

    • Positive work

    • Passive elastic mechanisms

    Daley, M. A. et al. J Exp Biol 2003;206:2941-2958


    Terrestrial posture l.jpg

    Terrestrial posture

    • Support body against gravity

    • Perturbation control

      • External (wind)

      • Internal (respiration, muscle)

    • Small movements


    Motor proteins l.jpg

    Motor proteins

    • Kinesin, dynein, myosin

    • Globular head

      • Filament binding & ATPase

    • Cargo-carrying tail

    Myosin

    Kinesin


    Myofilament structure l.jpg

    Myofilament structure

    • Myosin polymers arrange motor domains to maximize interaction with actin filament

    200 nm


    Structural homogeneity l.jpg

    Structural homogeneity

    • Structural order yield functional consistency

      • Narrow range of sarcomere “strength”

      • Minimizes intra-muscular force loss


    Sliding filament theory l.jpg

    Z

    I

    A

    I

    Sliding filament theory

    • Force varies in proportion to crossbridge binding


    Crossbridge cycle l.jpg

    Crossbridge cycle

    • ATP driven, ratchet motion

    • Mechanochemical coupling by crossbridge elasticity


    Crossbridge cycle16 l.jpg

    Crossbridge Cycle

    Hydrolysis of ATP energizes myosin; moves crossbridge

    ATP binding to myosin displaces actin

    Energized myosin binds actin

    Myosin binds actin strongly (rigor)

    Release of inorganic phosphate triggers power stroke


    Fundamental reactions l.jpg

    Fundamental reactions

    • Actin-myosin association

      • Slow (20 ms)

      • All or none change in force

    • Power stroke

      • Fast (1 ms)

      • Modulatory

    A rapid shortening pushes crossbridges through the power stroke. These crossbridges rapidly accommodate the change and are slowly displaced by new crossbridges


    Isotonic shortening l.jpg

    Isotonic shortening

    • Muscle can shorten against less load than it can hold.

    • Stimulate muscle

    • Allow force to stabilize

    • Release against

      constant load

    Magnetic

    catch

    Counterweight

    Muscle


    Dynamic response of muscle l.jpg

    1.8

    1.6

    1.4

    1.2

    Po

    100

    00

    1.0

    Force

    Force response

    0.8

    500

    0.6

    0

    0.4

    0.2

    0.2

    0

    (mm)

    Vmax

    L

    0.0

    D

    0

    100

    200

    300

    400

    -0.5

    0

    0.5

    1

    Time (ms)

    Applied length

    Shortening Velocity

    Dynamic response of muscle

    • Isotonic force velocity relation

    • Stretch and hold response

    Force (mN)


    Engineering analog l.jpg

    1.8

    1.6

    1.4

    1.2

    Po

    Force

    1.0

    0.8

    0.6

    0.4

    0.2

    Vmax

    0.0

    -0.5

    0

    0.5

    1

    Shortening Velocity

    Engineering analog

    • “Force-length” is like stiffness

    • “Force-velocity” is like viscosity

    F=Fo-bv

    F=kx


    Phenomenological hill model l.jpg

    Phenomenological (Hill) Model

    • Linear model

      • Force-length spring constant

      • Force-velocity viscosity

    • Standard linear solid analogy

      • Contractile Force-length

      • Contractile Force-velocity

      • Elastic elements account for dynamics


    Control of activation l.jpg

    Control of activation

    • Troponin/tropomyosin complex

      • Bind actin

      • Block myosin

      • Calcium dependent


    Calcium control l.jpg

    Calcium control

    • Contractile dynamics are calcium dependent

    • Efficient contraction requires homogeneous calcium transients

    • Sarcoplasmic reticulum

    • T-Tubules


    Excitation contraction coupling l.jpg

    Excitation contraction coupling

    • Synaptic discharge initiates action potential

    • V-gated Ca2+ channels open

    • Ca2+ bind TnC

    • Force generation

    • Recovery

    Action potential

    Calcium

    Force


    Force summation l.jpg

    Force summation

    • Nonlinear addition of subsequent APs


    Force frequency l.jpg

    Force Frequency

    • Muscle & species dependent

    • Myosin kinetics

    • Calcium kinetics


    Whole muscle organization l.jpg

    Whole muscle organization

    • Physical

      • Fiber

      • Fascicle

      • Muscle

      • Agonist

    • Neural

      • Motor unit

      • Compartment

      • Muscle

      • Synergy


    Motor unit l.jpg

    Motor Unit

    • Alpha motorneuron

      • Large (12-20 um)

      • High CV (70-120 m/s)

    • Innervated muscle fibers

      • 10-1000 fibers/neuron

      • Generally proportional to axon size

      • Generally of similar function

    • 5-1000s per muscle

    MN

    Innervated fibers


    Whole muscle force modulation l.jpg

    Whole muscle force modulation

    • Rate

      • Force-frequency

      • Continuous control

    • Recruitment

      • Select subpopulation of MU

      • Force sharing

      • Metabolic optimization

      • Size principle


    Motor unit control l.jpg

    Motor unit control

    • Smooth force generation

      • Individual MUs sub-tetanic

      • Rate & phase variation


    Electrical stimulation l.jpg

    Electrical stimulation

    • Recruitment

      • Axonal input resistance

      • Capacitance

    • Synchrony

    • Recruitment modulation

      • Intensity

      • Pulse width

      • High frequency block


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