Free nerve endings in the epidermis terminate in the stratum granulosum. The endings are “free” in that they lack a connective tissue or Schwann cell investment. Such neuronal endings subserve multiple sensory modalities including fine touch, heat, and cold, without apparent morphologic distinction. Networks of free dermal endings surround most hair follicles and attach to their outer root sheath (Fig. 15.12). In this position, they are particularly sensitive to hair movement and serve as mechanoreceptors. This relationship imparts a sophisticated degree of specialization in the receptors that surround tactile hairs (vibrissae), such as the whiskers of a cat or rodent, in which each vibrissa has a specific representation in the cerebral cortex.
Other nerve endings in the skin are enclosed in a connective tissue capsule. Encapsulated nerve endings include the following: tions applied on the skin surface.  Meissner’s corpuscles are responsible for sensitivity to light touch. Ruffni’s corpuscles that sensitive to skin stretch and torque.
Pacinian corpuscles are deep pressure receptors for mechanical and vibratory pressure.
Pacinian corpuscles are large ovoid structures found in the deeper dermis and hypodermis (especially in the fingertips), in connective tissue in general, and in association with joints, periosteum, and internal organs. Pacinian corpuscles usually have macroscopic dimensions, measuring more than 1 mm along their long axis. They are composed of a myelinated nerve ending surrounded by a capsule structure (see Figs. 15.11 and 15.12a). The nerve enters the capsule at one pole with its myelin sheath intact. The myelin is retained for one or two nodes and is then lost. The unmyelinated portion of the axon extends toward the opposite pole from which it entered, and its length is covered by a series of tightly packed, flattened Schwann cell lamellae that form the inner core of the corpuscle. The remainder or bulk of the capsule, the outer core, is formed by a series of concentric lamellae; each lamella is separated
Merkel’s cell free endings of afferent axon terminal disk of afferent axon terminal of afferent axon b terminal branches of afferent axon dermal papilla terminal branches of afferent axon spiral terminals of afferent axon
FIGURE 15.11 • Diagram of the sensory receptors in skin.
from its neighbor by a narrow space containing lymphlike fluid (Plate 46, page 523). The appearance of the concentric lamellae as observed in the light microscope is reminiscent of the cut surface of a hemisected onion. Each lamella is composed of flattened cells that correspond to the cells of the endoneurium outside the capsule. In addition to fluid between the lamellae, collagen fibrils are present, although sparse, as are occasional capillaries.
Pacinian corpuscles respond to pressure and vibration through the displacement of the capsule lamellae. This displacement effectively causes depolarization of the axon.
Meissner’s corpuscles are localized within dermal papillae and serve as touch receptors.