Clinical Laboratory for Bionic Extremity Reconstruction, Department of Plastic, Reconstructive and Aesthetic Surgery, Medical University of Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria; Center for Biomedical Research, Medical University of Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria.
Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria.
J Adv Res. 2023 Feb;44:135-147. doi: 10.1016/j.jare.2022.04.009. Epub 2022 Apr 22.
Neuromuscular control of the facial expressions is provided exclusively via the facial nerve. Facial muscles are amongst the most finely tuned effectors in the human motor system, which coordinate facial expressions. In lower vertebrates, the extracranial facial nerve is a mixed nerve, while in mammals it is believed to be a pure motor nerve. However, this established notion does not agree with several clinical signs in health and disease.
To elucidate the facial nerve contribution to the facial muscles by investigating axonal composition of the human facial nerve. To reveal new innervation pathways of other axon types of the motor facial nerve.
Different axon types were distinguished using specific molecular markers (NF, ChAT, CGRP and TH). To elucidate the functional role of axon types of the facial nerve, we used selective elimination of other neuronal support from the trigeminal nerve. We used retrograde neuronal tracing, three-dimensional imaging of the facial muscles, and high-fidelity neurophysiological tests in animal model.
The human facial nerve revealed a mixed population of only 85% motor axons. Rodent samples revealed a fiber composition of motor, afferents and, surprisingly, sympathetic axons. We confirmed the axon types by tracing the originating neurons in the CNS. The sympathetic fibers of the facial nerve terminated in facial muscles suggesting autonomic innervation. The afferent fibers originated in the facial skin, confirming the afferent signal conduction via the facial nerve.
These findings reveal new innervation pathways via the facial nerve, support the sympathetic etiology of hemifacial spasm and elucidate clinical phenomena in facial nerve regeneration.
面部表情的神经肌肉控制仅由面神经提供。面部肌肉是人类运动系统中最精细的效应器之一，它们协调面部表情。在较低等的脊椎动物中，颅外面神经是混合神经，而在哺乳动物中，它被认为是纯运动神经。然而，这一既定概念与健康和疾病中的几种临床症状并不相符。
通过研究人类面神经的轴突组成，阐明面神经对面部肌肉的贡献。揭示运动面神经的其他轴突类型的新神经支配途径。
使用特定的分子标志物（NF、ChAT、CGRP 和 TH）区分不同的轴突类型。为了阐明面神经轴突类型的功能作用，我们使用选择性消除三叉神经中的其他神经元支持。我们使用逆行神经元追踪、面部肌肉的三维成像和动物模型中的高保真神经生理测试。
人类面神经显示出只有 85%的运动轴突的混合群体。啮齿动物样本显示出运动、传入和令人惊讶的交感神经轴突的纤维组成。我们通过追踪中枢神经系统中的起源神经元来确认轴突类型。面神经的交感纤维终止于面部肌肉，表明存在自主神经支配。传入纤维起源于面部皮肤，证实了通过面神经的传入信号传导。
这些发现揭示了面神经的新神经支配途径，支持面肌痉挛的交感病因，并阐明了面神经再生中的临床现象。
