Number and diameter distribution of myelinated afferent fibers innervating the paws of the cat and monkey

Abstract

The number and the diameter distribution of the myelinated cutaneous fibers innervating fore and hind paw were histologically examined in the cat and monkey. In five cats, the superficial peroneal nerve innervating the dorsal surface of the hind paw and the superficial plantar nerve innervating the palmar surface were composed of 2668–2950 fibers, 40–44% of which were group II fibers. On the other hand, the superficial radial nerve innervating the dorsal surface of the fore paw and the sensory branch of median nerve innervating the palmar surface were composed of 3270–3680 fibers, of which 67–72% were group II fibers. Therefore, it was found that the cutaneous fore paw nerves contained more group II fibers than the hind paw cutaneous nerves. In five monkeys the percentages of group II fibers composing the superficial peroneal nerve and superficial plantar nerve (2893–3374 fibers) were the same as those of the hind paw nerves in the cat. On the other hand, the percentages of group II fibers of the median nerve (4173–4472 fibers) were 75–78%, about 10% larger than those of the superficial radial nerve (3596–3821 fibers) whose values were 66–69%. Therefore, in the monkey, the forepaw nerves innervating the palmar surface also contain more group II afferent fibers compared to the ones innervating the dorsal one (hairy skin).