The selectivity of fusimotor innervation in muscle spindles of the rat studied by light microscopy.

AUTOR(ES)

Arbuthnott, E R

RESUMO

Six muscle spindles and three muscle spindle poles from four rat soleus muscles have been sectioned serially at 1 micron intervals to trace the motor innervation by light microscopy. Forty myelinated axons had 92 endings on the intrafusal muscle fibres. 67.5% of these axons supplied a single type of muscle fibre only, 22.5% to dynamic bag1 (Db1) fibres, 15% to static bag2 (Sb2) fibres and 30% to chain fibres. The rest supplied more than one fibre type, 5% supplying the Db1 and one chain fibre, 20% supplying the Sb2 and chain fibres, but 7.5% (three axons) supplied all the fibre types together. Apart from these three axons all the fusimotor axons would be expected to have a clear dynamic or static action on the Group Ia discharge. Whilst for the cat entirely non-specific distribution does not exist, or at least is very rare, since only a small proportion of the rat fusimotor axons were in this category we conclude that fusimotor distribution in rats and cats is essentially similar.

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