Shinoda Y, Sugiuchi Y, Futami T, Ando N, Yagi J
Department of Physiology, School of Medicine, Tokyo Medical and Dental University, Japan.
J Neurophysiol. 1997 Mar;77(3):1234-58. doi: 10.1152/jn.1997.77.3.1234.
To reveal patterns of input from the six semicircular canals to motoneurons of various neck muscles and their relationship to the mechanical actions of individual neck muscles, patterns of input to neck motoneurons of the longissimus and the semispinalis muscle groups were investigated in the upper cervical spinal cord of anesthetized cats. Intracellular potentials were recorded from motoneurons of the longissimus muscle group (obliquus capitis superior muscle, OCS; splenius muscle, SPL; longissimus muscle, LONG) and the semispinalis muscle group (biventer cervicis muscle, BIV; complexus muscle, COMP), and effects of separate electrical stimulation of the six ampullary nerves on them were analyzed in each preparation. Neck motoneurons usually received convergent inputs from all of the six ampullary nerves, and motoneurons that supplied a particular muscle had a homogeneous pattern of input from the six ampullary nerves. Two different patterns of input were identified for motoneurons of these two muscle groups; one pattern for motoneurons of the longissimus muscle group and the other pattern for motoneurons of the semispinalis muscle group. Motoneurons of the OCS, the SPL, and the LONG muscles received excitation from the three contralateral ampullary nerves and inhibition from the three ipsilateral ampullary nerves. BIV and COMP motoneurons received excitation from the bilateral anterior canal nerves (ACNs) and the contralateral canal nerve (LCN) and inhibition from the bilateral posterior canal nerves (PCNs) and the ipsilateral LCN. Latencies of postsynaptic potentials (PSPs) evoked by stimulation of each of the six ampullary nerves indicated that the earliest component of excitatory PSPs (EPSPs) and inhibitory PSPs (IPSPs) was disynaptic in these motoneurons. However, trisynaptic IPSPs were evoked by stimulation of the contralateral PCN in a considerable number of BIV and COMP motoneurons. In OCS, SPL, and LONG motoneurons, all of the excitation from the contralateral and all of the inhibition from the ipsilateral ampullary nerves were mediated through the ipsilateral medial longitudinal fascicle (MLF). In BIV and COMP motoneurons, disynaptic excitation from the contralateral ACN and LCN and disynaptic inhibition from the ipsilateral LCN and bilateral PCNs were mediated through the ipsilateral MLF, whereas disynaptic excitation from the ipsilateral ACN was mediated through the ipsilateral lateral vestibulospinal tract. The patterns of semicircular canal input to neck motoneurons of these two muscle groups are related closely to the mechanical actions of the individual neck muscles and the optimal stimulus to the semicircular canals such that the connections will tend to stabilize head positions in response to head perturbations.
为揭示来自六个半规管的输入至各颈部肌肉运动神经元的模式及其与各颈部肌肉机械作用的关系，我们在麻醉猫的上颈脊髓中研究了输入至最长肌和半棘肌肌群颈部运动神经元的模式。记录了最长肌肌群（头上方斜肌，OCS；夹肌，SPL；最长肌，LONG）和半棘肌肌群（颈二腹肌，BIV；头后小直肌，COMP）运动神经元的细胞内电位，并在每个标本中分析了分别电刺激六条壶腹神经对它们的影响。颈部运动神经元通常从所有六条壶腹神经接收汇聚输入，且支配特定肌肉的运动神经元从六条壶腹神经接收的输入模式具有同质性。已确定这两个肌肉群的运动神经元有两种不同的输入模式；一种是最长肌肌群运动神经元的模式，另一种是半棘肌肌群运动神经元的模式。OCS、SPL和LONG肌肉的运动神经元从三条对侧壶腹神经接收兴奋，从三条同侧壶腹神经接收抑制。BIV和COMP运动神经元从双侧前半规管神经（ACN）和对侧半规管神经（LCN）接收兴奋，从双侧后半规管神经（PCN）和同侧LCN接收抑制。刺激六条壶腹神经中每条所诱发的突触后电位（PSP）潜伏期表明，在这些运动神经元中，兴奋性PSP（EPSP）和抑制性PSP（IPSP）的最早成分是双突触的。然而，在相当数量的BIV和COMP运动神经元中，刺激对侧PCN可诱发三突触IPSP。在OCS、SPL和LONG运动神经元中，来自对侧的所有兴奋和来自同侧壶腹神经的所有抑制均通过同侧内侧纵束（MLF）介导。在BIV和COMP运动神经元中，来自对侧ACN和LCN的双突触兴奋以及来自同侧LCN和双侧PCN的双突触抑制通过同侧MLF介导，而来自同侧ACN的双突触兴奋通过同侧外侧前庭脊髓束介导。这两个肌肉群颈部运动神经元的半规管输入模式与各颈部肌肉的机械作用以及对半规管的最佳刺激密切相关，从而使这些连接倾向于在头部受到扰动时稳定头部位置。
