Trulsson M, Essick G K
Dept. of Dental Medicine, Karolinska Institutet, Box 4064, S-14104 Huddinge, Sweden.
J Neurophysiol. 2010 Apr;103(4):1741-7. doi: 10.1152/jn.01146.2009. Epub 2010 Feb 3.
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.
对支配面部、牙齿、唇或口腔黏膜的下牙槽神经和舌神经中的单根传入轴突进行神经内微神经图记录和微刺激。使用自然机械刺激，根据单位类型[快适应I型（FA I）、FA毛、慢适应I型和II型（SA I和SA II）、牙周和深部舌单位]以及感受野的大小和形状，对35根单机械感受传入纤维进行了特征描述。随后，对所有传入纤维用30Hz的脉冲串持续刺激1.0秒。此后记录稳定的传入纤维还接受了5Hz和60Hz的单脉冲和脉冲串测试。结果显示，对面部区域的单根FA I、FA毛和SA I传入纤维进行电刺激可诱发一种感觉，该感觉在空间上与传入纤维的感受野相匹配，并且与自然机械刺激时观察到的传入纤维的反应特性一致。刺激FA传入纤维通常诱发本质上为振动的感觉；而SA I传入纤维的刺激则被感觉为持续压力。这些传入纤维在口腔面部组织中浅部终止，似乎对感知水平有特别强大的影响。相比之下，对单根牙周、SA II和深部舌传入纤维进行微刺激未能诱发与传入纤维感受野相匹配的感觉。这些传入纤维在组织中终止更深，在没有外部刺激时常常活跃，并且可能仅在多个传入纤维被刺激时才影响感知水平。有人提出，监测胶原纤维张力的自发活动传入纤维（SA II和牙周传入纤维）可能具有记录软组织机械状态的作用，据推测这有助于在中枢体感系统中维持身体的表征。
