Distribution of sole Pacinian corpuscles: a histological study using near-term human feet.

Introduction: Fast-adapting afferent input from the sole Pacinian corpuscles (PCs) is essential for walking. However, the distribution of PCs in the plantar subcutaneous tissue remains unknown.

Materials And Methods: Using histological sections tangential to the plantar skin of eight near-term fetuses, we counted 528-900 PCs per sole.

Results: Almost half of the sole PCs existed at the level of the proximal phalanx, especially on the superficial side of the long flexor tendons and flexor digitorum brevis. Conversely, the distribution was less evident on the posterior side of the foot. The medial margin of the sole contained fewer PCs than the lateral margin, possibly due to the transverse arch. In contrast to a cluster formation in the anterior foot, posterior PCs were almost always solitary, with a distance greater than 0.5 mm to the nearest PC.

Discussion And Conclusion: Because a receptive field of PCs is larger than that of the other receptors, fewer solitary PCs might cover the posterior sole. In infants, the amount of anterior sole PCs seemed to determine the initial walking pattern using the anterior foot without heel contact. Anterior PCs concentrated along flexor tendons might play a transient role as tendon organs during the initial learning of walking. During a lesson in infants, mechanical stress from the tendon and muscle was likely to degrade the PCs. In the near term, the sole PCs seemed not to be a mini-version of the adult morphology but suggested an infant-specific function.