Butler Jane E, Gandevia Simon C
Prince of Wales Medical Research Institute and University of New South Wales, Sydney, Australia.
J Physiol. 2008 Mar 1;586(5):1257-64. doi: 10.1113/jphysiol.2007.145789. Epub 2007 Nov 1.
Survival requires adequate pulmonary ventilation which, in turn, depends on adequate contraction of muscles acting on the chest wall in the presence of a patent upper airway. Bulbospinal outputs projecting directly and indirectly to 'obligatory' respiratory motoneurone pools generate the required muscle contractions. Recent studies of the phasic inspiratory output of populations of single motor units to five muscles acting on the chest wall (including the diaphragm) reveal that the time of onset, the progressive recruitment, and the amount of motoneuronal drive (expressed as firing frequency) differ among the muscles. Tonic firing with an inspiratory modulation of firing rate is common in low intercostal spaces of the parasternal and external intercostal muscles but rare in the diaphragm. A new time and frequency plot has been developed to depict the behaviour of the motoneurone populations. The magnitude of inspiratory firing of motor unit populations is linearly correlated to the mechanical advantage of the intercostal muscle region at which the motor unit activity is recorded. This represents a 'neuromechanical' principle by which the CNS controls motoneuronal output according to mechanical advantage, presumably in addition to the Henneman's size principle of motoneurone recruitment. Studies of the genioglossus, an obligatory upper airway muscle that helps maintain airway patency, reveal that it receives simultaneous inspiratory, expiratory and tonic drives even during quiet breathing. There is much to be learned about the neural drive to pools of human inspiratory and expiratory muscles, not only during respiratory tasks but also in automatic and volitional tasks, and in diseases that alter the required drive.
生存需要足够的肺通气，而肺通气又依赖于在气道通畅的情况下，作用于胸壁的肌肉的充分收缩。直接和间接投射到“必需的”呼吸运动神经元池的延髓脊髓输出产生所需的肌肉收缩。最近对作用于胸壁的五块肌肉（包括膈肌）的单个运动单位群体的相位吸气输出的研究表明，不同肌肉在起始时间、渐进性募集以及运动神经元驱动量（以放电频率表示）方面存在差异。在胸骨旁和肋间外肌的低肋间间隙中，具有吸气放电频率调制的紧张性放电很常见，但在膈肌中很少见。已经开发出一种新的时间和频率图来描绘运动神经元群体的行为。运动单位群体的吸气放电幅度与记录运动单位活动的肋间肌区域的机械优势呈线性相关。这代表了一种“神经力学”原理，即中枢神经系统根据机械优势控制运动神经元输出，大概除了亨内曼运动神经元募集的大小原则之外。对颏舌肌（一种有助于维持气道通畅的必需的上气道肌肉）的研究表明，即使在安静呼吸期间，它也会同时接受吸气、呼气和紧张性驱动。关于人类吸气和呼气肌肉群的神经驱动，还有很多需要了解的，不仅是在呼吸任务期间，还包括在自动和自主任务中，以及在改变所需驱动的疾病中。
