The Pacinian corpuscle has a framework of cytoplasmic lamellae arranged concentrically in the outer zone, and bilaterally in the core. Between these is an intermediate growth zone. The inner core shows an unexpected complexity in that its component lamellae are arranged in two symmetrical groups of nested cytoplasmic sheets. Longitudinal tissue spaces form clefts separating the two groups. The perikarya of the core lamellae lie in or near the intermediate growth zone, and send arms into the clefts. The arms then branch and terminate as lamellae which interdigitate with those of neighboring cells. The single nerve fiber loses its myelin sheath just before it reaches the inner core but retains its Schwann cell cytoplasmic covering for a short additional distance. The Schwann sheath is not continuous with the lamellae of the inner core. Inside the core the fiber contains a striking circumferential palisade of radially disposed mitochondria. The fiber does not arborize. Vascular capillaries penetrate the hilar region of the corpuscle only as far as the myelinated sheath of the nerve, and they have not been seen elsewhere in the corpuscle. There is direct continuity between the clefts of the core and tissue spaces in the vicinity of the capillaries. It is likely that this provides a route whereby metabolites reach the active nerve ending, as well as the cells of the growth zone. The outer zone consists of at least 30 flattened concentric cytoplasmic lamellae separated from one another by relatively wide fluid-filled spaces. Collagenous fibrils are present, particularly on the outer surface of lamellae, and tend to be oriented circularly. The girdle of proliferating cells constituting the growth zone, which is prominent in corpuscles from young animals, is the layer from which the outer lamellae are derived. Osmotic forces probably elevate the lamellae, and maintain turgor pressure.

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Gray & Sato (1953) recorded potentials from nerve fibres at the points where they left Pacinian corpuscles; when the Pacinian corpuscles were stimulated mechanically, they observed potentials which had three phases. The first of these phases, called the receptor potential, was graded to the stimulus strength, while the second and third phases represented diphasic impulse activity. On indirect evidence they assumed that the site of recording lay between the 'non-myelinated' terminal and the first node of Ranvier, and consequently that the receptor potential and the second phase were generated in the 'nonmyelinated' terminal, while the third phase originated from the first node of Ranvier.It is surprising that comparatively little is known about those histological features of the nerve fibre, which are necessary for the full interpretation of the potentials mentioned above; this, in spite of the fact that the presence of Pacinian corpuscles was first detected over two centuries ago (Lehmann, 1741) and that their histological appearance has been described in considerable detail on a number of occasions during the last 120 years (

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