Schematic illustration of receptors (endings of peripheral branches of primary afferent neurons, capable of converting environmental energy into neural excitation). Free nerve endings (upper left) are shown extending into the epidermis. Tactile corpuscles (lower left) involve epidermal cells transformed into sensory cells by nerve endings. Encapsulated receptors (right) consist of nerve endings encapsulated by lemmocytes and perineural epithelium in various configurations in order to modify the mechanical sensory response.