Mitchell R A, Berger A J
Am Rev Respir Dis. 1975 Feb;111(2):206-24. doi: 10.1164/arrd.1975.111.2.206.
The main respiratory muscles are under both voluntary and involuntary (automatic) control. These two control systems come from separate sites in the CNS and have separate descending pathways; the final integration of these outputs occurs at segmental levels in the cord. Voluntary control arises from the motor and premotor cortex and descends in the cord in the corticospinal tract. Involuntary control is mediated by both rhythmic and nonrhythmic systems located in the brainstem. Recent studies have associated the classic respiratory centers with specific nuclei in the brainstem. The pneumotaxic center is located in the nucleus parabrachialis, and the medullary respiratory centers are located in the vicinity of the nucleus of the solitary tract (dorsal respiratory group) and the nuclei ambiguus and retroambigualis (ventral respiratory group). Most axons from the medullary nuclei cross in the medulla and descend in the ventral and lateral columns to segmental levels. The classic medullary respiratory centers described by Pitts have been shown to be the site of origin of tonically firing long reticulospinal axons that descend in the ventral and lateral columns. This system is thought to provide a nonrhythmic involuntary biasing of the membrane potential of respiratory motoneurons in the cord. The site of generation of eupnic breathing and the mechanism of rhythm generation remain unknown. However, recent studies indicate that reciprocal inhibition between populations of inspiratory and expiratory cells (bistable oscillator model) does not occur in the medulla; rather we suggest that inhibitory phasing of inspiratory cells generates inspiratory rhythm, and periodic inhibition of tonically active expiratory neurons results in respiratory rhythm. We suggest that the inhibitory phasing occurs in the dorsal respiratory group, which is also the site of integration of respiratory afferents. The main site of integration of the voluntary and involuntary control systems is the cord where the respiratory motoneuron output is determined by descending information from these systems, as well as with intrasegmental and intersegmental reflexes. Separation of the voluntary and involuntary control systems also occurs in man and discrete lesions may interrupt one system without significant alteration of the other.
主要呼吸肌受自主和非自主（自动）控制。这两种控制系统来自中枢神经系统的不同部位，具有各自独立的下行通路；这些输出的最终整合发生在脊髓的节段水平。自主控制起源于运动皮层和运动前区皮层，并通过皮质脊髓束在脊髓下行。非自主控制由位于脑干的节律性和非节律性系统介导。最近的研究已将经典呼吸中枢与脑干中的特定核团联系起来。呼吸调整中枢位于臂旁核，延髓呼吸中枢位于孤束核（背侧呼吸组）以及疑核和后疑核（腹侧呼吸组）附近。来自延髓核团的大多数轴突在延髓交叉，并在腹侧和外侧柱下行至节段水平。皮茨描述的经典延髓呼吸中枢已被证明是在腹侧和外侧柱下行的持续性放电的长网状脊髓轴突的起源部位。该系统被认为为脊髓中呼吸运动神经元的膜电位提供非节律性的非自主偏倚。平静呼吸的产生部位和节律产生机制仍然未知。然而，最近的研究表明，吸气和呼气细胞群之间的相互抑制（双稳态振荡器模型）并非发生在延髓；相反，我们认为吸气细胞的抑制相位产生吸气节律，而对持续性活动的呼气神经元的周期性抑制导致呼吸节律。我们认为抑制相位发生在背侧呼吸组，它也是呼吸传入纤维的整合部位。自主和非自主控制系统的主要整合部位是脊髓，在脊髓中，呼吸运动神经元的输出由来自这些系统的下行信息以及节段内和节段间反射决定。自主和非自主控制系统在人类中也相互分离，离散性病变可能会中断一个系统而不会对另一个系统产生显著改变。
