Dynamic Bag 1 Fibre Response. Dynamic fusimotor stimulation causes local intrafusal contraction which stiffens the polar regions, but has little effect on the primary region. When stretch is maintained the polar regions 'creep' and the primary endings unload slightly. This is the basis of slow mechanical adaptation. Dynamic bag fibres are sensitive to change in length and this is enhanced by dynamic fusimotor stimulation.
Secondary afferents are rather less important.
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