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📚 > Physiology > Muscle Physiology > Skeletal Muscles_>

Alpha Gamma Coactivation



Motor Suppy to the Muscle

α (alpha) motor nueron

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Supplies extrafusal fibers

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Cause muscle contraction


γ (gamma) motor neuron

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Supplies intrafusal fibers

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Cause contraction of contractile ends of intrafusal fibers

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Maintains tension in muscle spindle


Alpha-Gamma Coactivation

As such activation of only α (alpha) motor neuron is required for voluntary muscle contraction.

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Yet, the upper motor neuron activates both, α (alpha) and γ (gamma) motor neurons simultaneously for voluntary muscle contraction.

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This is called alpha-gamma coactivation

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It keeps the muscle spindle sensitive to stretch over a wide range of muscle length.


Without Concurrent Activation of γ (gamma) Motor Neuron

Activation of only α (alpha) motor neuron

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Stimulation of extrafusal fibers

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Muscle contraction

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Shortening of muscle spindle

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Sensory endings on the muscle spindle become slack i.e. become loose

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In this state the sensory endings are not sensitive to changes in muscle length

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Stretch reflex cannot work properly when the muscle is contracted

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This is prevented by concurrent activation of γ (gamma) motor neuron along with α (alpha) motor neuron


With Concurrent Activation of γ (gamma) Motor Neuron

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Contraction of contractile ends of intrafusal muscle fibers

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Stretches the central region of muscle spindle

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Keeps the sensory endings in muscle spindle taut even though the entire muscle is contracted

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In this state the muscle spindle continues to be sensitive to stretch

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Stretch reflex can work properly when the muscle is contracted.


  • Thus alpha-gamma coactivation helps maintain normal stretch reflex over a wide range of initial muscle length.

 

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