Greer J J, Allan D W, Martin-Caraballo M, Lemke R P
Department of Physiology, University of Alberta, Edmonton, Canada T6G 2S2.
J Appl Physiol (1985). 1999 Mar;86(3):779-86. doi: 10.1152/jappl.1999.86.3.779.
In this overview, we outline what is known regarding the key developmental stages of phrenic nerve and diaphragm formation in perinatal rats. These developmental events include the following. Cervical axons emerge from the spinal cord during embryonic (E) day 11. At approximately E12.5, phrenic and brachial axons from the cervical segments merge at the brachial plexi. Subsequently, the two populations diverge as phrenic axons continue to grow ventrally toward the diaphragmatic primordium and brachial axons turn laterally to grow into the limb bud. A few pioneer axons extend ahead of the majority of the phrenic axonal population and migrate along a well-defined track toward the primordial diaphragm, which they reach by E13.5. The primordial diaphragmatic muscle arises from the pleuroperitoneal fold, a triangular protrusion of the body wall composed of the fusion of the primordial pleuroperitoneal and pleuropericardial tissues. The phrenic nerve initiates branching within the diaphragm at approximately E14, when myoblasts in the region of contact with the phrenic nerve begin to fuse and form distinct primary myotubes. As the nerve migrates through the various sectors of the diaphragm, myoblasts along the nerve's path begin to fuse and form additional myotubes. The phrenic nerve intramuscular branching and concomitant diaphragmatic myotube formation continue to progress up until E17, at which time the mature pattern of innervation and muscle architecture are approximated. E17 is also the time of the commencement of inspiratory drive transmission to phrenic motoneurons (PMNs) and the arrival of phrenic afferents to the motoneuron pool. During the period spanning from E17 to birth (gestation period of approximately 21 days), there is dramatic change in PMN morphology as the dendritic branching is rearranged into the rostrocaudal bundling characteristic of mature PMNs. This period is also a time of significant changes in PMN passive membrane properties, action-potential characteristics, and firing properties.
在本综述中，我们概述了围产期大鼠膈神经和膈肌形成的关键发育阶段的已知情况。这些发育事件包括以下内容。颈轴突在胚胎（E）第11天从脊髓发出。在大约E12.5时，来自颈段的膈神经和臂神经轴突在臂丛处汇合。随后，随着膈神经轴突继续向腹侧生长朝向膈肌原基，而臂神经轴突转向外侧生长进入肢芽，这两个群体分道扬镳。一些先驱轴突在大多数膈神经轴突群体之前延伸，并沿着一条明确的轨迹向原始膈肌迁移，它们在E13.5时到达原始膈肌。原始膈肌肌肉起源于胸腹皱襞，这是体壁的一个三角形突出物，由原始胸腹和胸心包组织融合而成。膈神经在大约E14时开始在膈肌内分支，此时与膈神经接触区域的成肌细胞开始融合并形成明显的初级肌管。随着神经迁移穿过膈肌的各个部分，沿神经路径的成肌细胞开始融合并形成额外的肌管。膈神经肌内分支和伴随的膈肌肌管形成一直持续到E17，此时神经支配和肌肉结构的成熟模式接近完成。E17也是吸气驱动传递至膈运动神经元（PMN）开始以及膈传入神经到达运动神经元池的时间。在从E17到出生（妊娠期约21天）期间随着树突分支重新排列成成熟PMN的头尾束状特征，PMN形态发生了显著变化。这个时期也是PMN被动膜特性、动作电位特性和放电特性发生重大变化的时期。
