1. The discharge of impulses in afferent fibres dissected from the infraorbital and ulnar nerves of anaesthetized cats was recorded during controlled movements of the maxillary and carpal sinus hairs.2. Four main types of afferent units were identified. Two had slowly adapting responses characteristic of the epidermal type I, and dermal type II mechanoreceptors of the hairy skin. Two rapidly adapting responses to movement of the sinus hairs were found, one with a high velocity threshold and another with a low velocity threshold.3. The slowly adapting units showed a power relationship between the degree of displacement of the hair and the mean interspike interval of the response. Slowly adapting units also exhibited a power relationship between the velocity of displacement of a hair and the mean interspike interval of the response.4. The conduction velocities of all types of afferent units were measured and fell in the range of the Aalpha, fast myelinated fibres.5. Movements of the carpal sinus hairs yielded both types of slowly adapting response recorded in fibres of the ulnar nerve directly innervating the carpal sinus hair follicles, and rapidly adapting responses from Pacinian corpuscles, found in close association with, but external to, these follicles.6. On the basis of the findings in this study and the results of anatomical investigations of the receptor structures in the sinus hair follicle a correlation between the distinguishable afferent responses and the morphologically identifiable nerve endings has been proposed.

An electron microscopic and electrophysiological investigation was made of Merkel cell-neurite complexes in the sinus hair follicles of the cat. These mechanoreceptors respond with very precise phase locking to heavy-frequency vibratory stimuli as well as to static hair displacements. The mechanoelectric transduction process is faster than that known for any other somatic mechanoreceptor. These data show that the nerve endings themselves and not the Merkel cells are the mechanoelectric transducer elements in these receptors.

No abstract

No abstract

An electrophysiological study on single afferent nerve fibers in the ophthalmic nerve of the goose revealed two kinds of temperature-sensitive mechanoreceptors in the beak, which are innervated by large-diameter myelinated axons. Some Herbst corpuscles, which display rapidly adapting responses to mechanical stimulation, discharge tonically to cooling the receptive field. A static response maximum occurs a t temperatures between 15 and 25 "C. The vibration sensitivity of Herbst corpuscles decreases with temperature. Many slowly adapting Ruffini endings also respond with sustained discharges to cooling but behave like rapidly adapting mechanoreceptors on warming the receptive field. The temperature a t which the maximal static response occurs in different slowly adapting units varies between 10 and 30 "C.The fine structure of Herbst corpuscles and Ruffini endings was investigated electron microscopically in order to elucidate possible morphological substrates for the specific functional properties of the two receptor types. Both Herbst corpuscles and Ruffini endings are characterized by a distinct but different combination of nervous and nonnervous (auxiliary) tissue elements and by the occurrence of special structural units a t the sensory nerve endings. Such "transducer sites" presumably correspond to those areas of the receptor membrane where the mechanoelectric transduction process takes place. The most prominent constituent of a transducer site is a spurlike axon process, which in the Herbst corpuscle projects between the lamellae of the inner core, and in the Ruffini endings comes into contact with collagenous microfibrils, either directly or indirectly through the mediation of Schwann cell processes.Two morphological variants of Ruffini endings were recognized and were found to occur a t different locations in the dermis underlying the horny covering of the bill tip. One type is distinguished by the presence of a specialized terminal cell making contact with the initial branches of the arborizing receptor axon. The other type of Ruffini ending lacks the terminal cell.The structure-function relations in Herbst corpuscles and Ruffini endings are discussed on the basis of the electrophysiological and ultrastructural observations. It is argued that the different response characteristics of both receptor types to mechanical stimuli result from the specific kind