Abstract
The functional, or true terminal innervation ratio (TIR) was estimated on 13 neuromuscular biopsies taken from 5 palmaris longus and 7 tibialis anterior muscles in 7 male and 6 female healthy young volunteers. Axonal ramification resulting in the innervation of more than 1 muscle fibre by 1 subterminal axon occurs in 10.6% of the total number of axons studied. Most of the branching axons (94%) innervate 2 muscle fibres. Only 5.1 of them supply 3 muscle fibres by trifurcation. Innervation of 4 muscle fibres by 1 ramified subterminal axon is extremely rare and was observed in 0.9% of branching fibres, i.e. in 0.1% of all axons studied. There is no significant difference between the TIR of palmaris longus and that of tibialis anterior, nor between the values obtained in males and females. A mean TIR of 1.12 was obtained (range 1.05–1.20). Statistical analysis indicates that values higher than 1.25 are outside the normal range of distribution.
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