Stuesse S L, Cruce W L, Powell K S
J Comp Neurol. 1983 Jul 10;217(4):432-9. doi: 10.1002/cne.902170407.
In amphibians, the spinomedullary region of the central nervous system is compressed rostrocaudally because of the absence of a neck. In Ranid frogs, the hypoglossal nerve emerges as the ventral ramus of the second spinal nerve. The first spinal nerve, though present in tadpoles, is absent as a separate nerve in adults. To investigate the central nervous system components of the hypoglossal nerve in Rana pipiens, we soaked identified, transected branches of this nerve in horseradish peroxidase, a retrograde and anterograde tracer. We found that the hypoglossal nerve in these frogs originates from two efferent nuclei located in the caudal medulla, a medial and a lateral one. Afferent fibers, primarily from the tongue, are also found in the hypoglossal nerve and travel in the dorsolateral funiculus of the spinal cord, descending to thoracic levels of the cord. Efferents to intrinsic tongue muscles and the genioglossus muscle originate in the medial medullary nucleus. Efferents to the sternohyoid muscle, which travel through the hypoglossal nerve, originate in the lateral medullary nucleus. Since in mammals the sternohyoid muscle is innervated by the first spinal nerve, we have obtained experimental evidence that the hypoglossal nerve in Rana pipiens contains components of this spinal nerve.
在两栖动物中，由于没有颈部，中枢神经系统的脊髓延髓区域在前后方向上受到挤压。在蛙科青蛙中，舌下神经作为第二对脊神经的腹支发出。第一对脊神经在蝌蚪中存在，但在成年青蛙中作为一条独立的神经不存在。为了研究牛蛙舌下神经的中枢神经系统组成部分，我们将该神经已确定的、横断的分支浸泡在辣根过氧化物酶中，辣根过氧化物酶是一种逆行和顺行示踪剂。我们发现，这些青蛙的舌下神经起源于位于延髓尾部的两个传出核，一个内侧核和一个外侧核。传入纤维主要来自舌头，也存在于舌下神经中，并在脊髓的背外侧索中走行，下行至脊髓的胸段。支配舌内肌和颏舌肌的传出纤维起源于延髓内侧核。支配胸骨舌骨肌的传出纤维通过舌下神经走行，起源于延髓外侧核。由于在哺乳动物中胸骨舌骨肌由第一对脊神经支配，我们获得了实验证据，证明牛蛙的舌下神经包含这条脊神经的组成部分。
