Department of Anesthesiology Mannheim, University Heidelberg, Mannheim.
Eur J Dermatol. 2011 May;21 Suppl 2:43-7. doi: 10.1684/ejd.2011.1265.
The skin is equipped with nerve fibers subserving the senses for touch, temperature, pain and itch. Thickly myelinated Aβ-fibers are linked to low threshold mechano-receptors responsible to detect vibration and slight indentation of the skin. Among the thinly myelinated Aδ-fibers one class is crucial for the cold detection, but there also nociceptive Aδ-fibers for the detection fast rising noxious heat and punctate mechanical stimuli. Unmyelinated C-fibers consist of various classes mediating nociceptive (pain and itch) and non-nociceptive (warmth, pleasant touch) sensations. The unmyelinated C-fibers have close contact to the keratinocytes and the interaction between C-fibers and local skin cells is of particular interest, as efferent neuronal function has both local trophic and immunomodulatory function. In turn, excitability of C-fibers is governed in part by neurotrophins from neighbouring skin cells such as keratinocytes. This mechanism is held responsible to induce and maintain chronic itch and pain conditions. Beyond this interaction recently a direct involvement of keratinocytes in the transduction process has been discussed especially for temperature and noxious stimuli, as keratinocytes express a variety of sensory transduction molecules. Thus, the interplay between neurons and non-neuronal cells is operational not only in basic physiology, but also in chronic itch and pain patients.
皮肤配备有神经纤维，负责触觉、温度、疼痛和瘙痒等感觉。厚髓鞘的 Aβ 纤维与低阈值机械感受器相连，后者负责检测皮肤的振动和轻微凹陷。在薄髓鞘的 Aδ 纤维中，有一种纤维对冷觉的检测至关重要，但也有伤害性 Aδ 纤维用于检测快速上升的有害热和点状机械刺激。无髓鞘的 C 纤维由各种介导伤害性（疼痛和瘙痒）和非伤害性（温暖、舒适触摸）感觉的类纤维组成。无髓鞘的 C 纤维与角质形成细胞密切接触，C 纤维与局部皮肤细胞之间的相互作用特别有趣，因为传出神经元的功能既有局部营养作用，也有免疫调节作用。反过来，C 纤维的兴奋性部分受来自邻近皮肤细胞（如角质形成细胞）的神经营养因子的调节。这种机制被认为是引起和维持慢性瘙痒和疼痛的原因。除此之外，最近还讨论了角质形成细胞在转导过程中的直接参与作用，特别是对于温度和有害刺激，因为角质形成细胞表达多种感觉转导分子。因此，神经元和非神经元细胞之间的相互作用不仅在基础生理学中起作用，而且在慢性瘙痒和疼痛患者中也起作用。
