Silver Wayne L, Finger Thomas E
Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109, USA.
Ann N Y Acad Sci. 2009 Jul;1170:202-5. doi: 10.1111/j.1749-6632.2009.03894.x.
The trigeminal nerve (TN) provides sensory information from the eyes, nose, and mouth. A subset of trigeminal nerve fibers, particularly those containing the neuropeptides substance P and calcitonin gene-related peptide (CGRP), responds to chemical irritants in the environment. Axons in the ethmoid and nasopalatine branches of the trigeminal nerve innervate the nasal mucosa where they ramify repeatedly. TN endings extend close to the nasal epithelial surface stopping at the line of tight junctions only a few micrometers from the surface. A single ethmoid nerve axon may send branches to the nasal mucosa, olfactory bulb, and the spinal trigeminal complex. Traditionally, irritants are thought to stimulate free TN endings in the nasal epithelium. Recently, however, solitary chemoreceptor cells (SCCs) have been found scattered throughout the nasal cavity. The SCCs are contacted by TN fibers and may express T2R ''bitter-taste'' receptors alpha-gustducin, and TRPM5. Peripheral trigeminal electrophysiological recordings in response to irritants have been obtained from the mucosa (negative mucosal potential, NMP) and the nerve to analyze characteristics of trigeminal stimuli. Responses to a wide variety of irritants have been recorded from the ethmoid nerve. In general, the more lipid soluble the compound, the lower the threshold. Nerve recordings have also suggested several mechanisms by which irritants elicit responses. Bitter substances elicit responses from the ethmoid nerve and cause a change in respiration indicating stimulation via SCCs. SCCs themselves respond to chemical stimuli and may be contributing to the detection of nasal irritants.
三叉神经（TN）负责传递来自眼睛、鼻子和嘴巴的感觉信息。三叉神经纤维的一个子集，特别是那些含有神经肽P物质和降钙素基因相关肽（CGRP）的纤维，对环境中的化学刺激物作出反应。三叉神经筛骨支和鼻腭支中的轴突支配鼻黏膜，并在其中反复分支。TN末梢靠近鼻上皮表面延伸，止于紧密连接线上，距表面仅几微米。单个筛骨神经轴突可能向鼻黏膜、嗅球和三叉神经脊束核发出分支。传统上，刺激物被认为会刺激鼻上皮中的游离TN末梢。然而，最近发现孤立化学感受器细胞（SCCs）散在于整个鼻腔中。SCCs与TN纤维接触，并可能表达T2R“苦味”受体、α - 味导素和瞬时受体电位阳离子通道亚家族M成员5（TRPM5）。已从黏膜（负黏膜电位，NMP）和神经获得对刺激物的外周三叉神经电生理记录，以分析三叉神经刺激的特征。已记录到筛骨神经对多种刺激物的反应。一般来说，化合物的脂溶性越高，阈值越低。神经记录还提示了刺激物引发反应的几种机制。苦味物质会引发筛骨神经的反应，并导致呼吸变化，表明通过SCCs产生刺激。SCCs自身对化学刺激有反应，可能有助于检测鼻腔刺激物。
