Intraneural microneurography and microstimulation were performed on single afferent axons in the inferior alveolar and lingual nerves innervating the face, teeth, labial, or oral mucosa. Using natural mechanical stimuli, 35 single mechanoreceptive afferents were characterized with respect to unit type [fast adapting type I (FA I), FA hair, slowly adapting type I and II (SA I and SA II), periodontal, and deep tongue units] as well as size and shape of the receptive field. All afferents were subsequently microstimulated with pulse trains at 30 Hz lasting 1.0 s. Afferents recordings whose were stable thereafter were also tested with single pulses and pulse trains at 5 and 60 Hz. The results revealed that electrical stimulation of single FA I, FA hair, and SA I afferents from the orofacial region can evoke a percept that is spatially matched to the afferent's receptive field and consistent with the afferent's response properties as observed on natural mechanical stimulation. Stimulation of FA afferents typically evoked sensations that were vibratory in nature; whereas those of SA I afferents were felt as constant pressure. These afferents terminate superficially in the orofacial tissues and seem to have a particularly powerful access to perceptual levels. In contrast, microstimulation of single periodontal, SA II, and deep tongue afferents failed to evoke a sensation that matched the receptive field of the afferent. These afferents terminate more deeply in the tissues, are often active in the absence of external stimulation, and probably access perceptual levels only when multiple afferents are stimulated. It is suggested that the spontaneously active afferents that monitor tension in collagen fibers (SA II and periodontal afferents) may have the role to register the mechanical state of the soft tissues, which has been hypothesized to help maintain the body's representation in the central somatosensory system.
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"Instead, it seems more likely that tiny particles could be detected by forces at contact because mechanoreceptors in the periodontal ligament that can detect these have been located (Trulsson & Essick 2010). In fact, periodontal receptors regularly respond, not to the scale of forces of mastication in general (Trulsson 2006), but to the range of sub-Newton forces (Trulsson & Johansson 1994, Trulsson & Essick 2010) that we have shown would be required to detect those particles that could cause wear (Lucas et al. 2013). "
"In contrast, the canines play a guiding role during lateral jaw movement. The inferior alveolar nerves were more sensitive to the central incisor stimulation than the canine (Trulsson and Essick, 2010). Thus, periodontal mechanoreceptors of the central incisors may carry more information than those of the canines, or the canine-driven PMR may be more strongly influenced by other proprioceptive factors from intra-and juxta-oral organs: e.g., the temporomandibular joint, muscle spindles, and tongue (Takada et al., 1996). "
[Show abstract][Hide abstract] ABSTRACT: Introduction:
The present study was designed to clarify whether the bilateral cooperation in the human periodontal-masseteric reflex (PMR) differs between central incisors and canines.
Surface array electrodes were placed on the bilateral masseter muscles to simultaneously record the firing activities of single motor units from both sides in seven healthy adults. During light clenching, mechanical stimulation was applied to the right maxillary central incisor and canine to evoke the PMR. Unitary activity was plotted with respect to the background activity and firing frequency. The slope of the regression line (sRL) and the correlation coefficient (CC) between the central incisor and canine and the lateral differences between these values were compared.
There were significant differences in the sRL and CC, as well as lateral differences, between the central incisor- and canine-driven PMR.
These results suggest that the PMR differs depending on both the tooth position and laterality.
Full-text · Article · Jun 2012 · Frontiers in Physiology
[Show abstract][Hide abstract] ABSTRACT: The human skin is innervated by a network of thin, slow-conducting afferent (C and Aδ) fibers, transmitting a diverse range of information. Classically, these fibers are described as thermo-, noci- or chemoreceptive, whereas mechanoreception is attributed exclusively to thick, fast-conducting (Aβ) afferents. A growing body of evidence, however, supports the notion that C tactile afferents comprise a second anatomically and functionally distinct system signaling touch in humans. This review discusses established as well as recent findings which highlight fundamental differences in peripheral and central information coding and processing between Aβ and C mechanoreception. We conclude that from the skin through the brain, C touch shares more characteristics with interoceptive modalities (e.g. pain, temperature, and itch) than exteroceptive Aβ touch, vision or hearing. In this light, we discuss the motivational-affective role of C touch as an integral part of a thin-fiber afferent homeostatic network for the maintenance of physical and social well-being.
No preview · Article · Oct 2010 · Experimental Brain Research