Peripheral projections of fascicles in the human median nerve.

Intraneural microstimulation combined with microneurography was employed to study the degree of mixing of muscle and skin nerve fibres at two levels in the human median nerve, and to delineate the area of skin supplied by a fascicle. It was found that about half the fascicles at upper arm level appeared to supply exclusively skin or muscle, while the remainder were considerably committed to one or the other. Further, the projection territories of skin nerve fascicles, both at the wrist and in the arm, tended to be discrete, confluent areas covering no more than 20 per cent of the median nerve territory. At the wrist fascicular territories usually resembled the innervation area of a single palmar digital nerve while in the upper arm they tended to cover a digital interspace. These findings suggest that most of the rearrangements of spinal root fibres into terminal nerve branch groupings occur at brachial plexus level, while the intraneural fascicular plexus may act as a safety mechanism allowing for nondermatomal overlap at proximal level.