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Alpha Gamma Coactivation



Motor Suppy to the Muscle

α (alpha) motor nueron

Supplies extrafusal fibers

Cause muscle contraction


γ (gamma) motor neuron

Supplies intrafusal fibers

Cause contraction of contractile ends of intrafusal fibers

Maintains tension in muscle spindle


Alpha-Gamma Coactivation

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

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

This is called alpha-gamma coactivation

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

Stimulation of extrafusal fibers

Muscle contraction

Shortening of muscle spindle

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

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

Stretch reflex cannot work properly when the muscle is contracted

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

Contraction of contractile ends of intrafusal muscle fibers

Stretches the central region of muscle spindle

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

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

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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Cardiovascular System > Organization of Cardiovascular System > ▶️ Introduction to Cardiovascular System

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