Lee K H, Chung K, Chung J M, Coggeshall R E
J Comp Neurol. 1986 Jan 15;243(3):335-46. doi: 10.1002/cne.902430305.
Measurements of cell body and peripheral and central axon sizes were made for primary sensory neurons outlined by the intracellular injection of HRP. Conduction velocities were also measured on the outlined processes. The sensory neurons were then subdivided into A and C cells on the basis of the conduction velocity of the impulses carried by the processes of these cells. Central processes of both A and C cells are smaller than the peripheral processes, but the size differential is greater for the C cells. For A cells there is a linear relation between the size of the peripheral axon and the conduction velocity of the impulses carried by these axons, but the confidence limits are wide. For C cells there is a linear relation between the size of the central process and conduction velocity of the impulses carried by the processes, but for the peripheral processes two aberrant processes resulted in no correlation between process size and conduction velocity. For A cells, the size of the central and peripheral processes and the conduction velocity of the impulses carried by the peripheral processes are linearly correlated with cell body size. By contrast no such correlations can be demonstrated for C cells. This presumably implies an important difference in that the size of the cell body is correlated with axon size and impulse conduction velocity for A cells but not for C cells. A widely accepted generalization is that large sensory cells give rise to myelinated axons and small sensory cells to unmyelinated axons. In this study, myelinated and unmyelinated are defined on the basis of impulse conduction velocity. For those cells that are clearly large (greater than 50 microns in diameter), the conduction velocity of the impulses carried by their processes is always greater than 2.5 m/s, and for those cells that are clearly small (less than 35 microns in diameter), the conduction velocity is always less than 2.5 m/s. Thus for these cells the above generalization holds. For the intermediate-sized cells (35-50 microns), however, the size of the cell body bears no predictable relation to the conduction velocity of the impulses carried by those processes, and thus to whether the axons are myelinated or unmyelinated. Thus the above generalization does not hold for this intermediate group of cells, and since there are many cells in this size range, we feel that the generalization that large cells give rise to myelinated axons and small cells to unmyelinated axons is an oversimplification.
对通过细胞内注射辣根过氧化物酶（HRP）勾勒出的初级感觉神经元的细胞体、外周和中枢轴突大小进行了测量。还对勾勒出的神经突起进行了传导速度测量。然后根据这些细胞的神经突起所携带冲动的传导速度，将感觉神经元细分为A类和C类细胞。A类和C类细胞的中枢神经突起都比外周神经突起小，但C类细胞的大小差异更大。对于A类细胞，外周轴突的大小与这些轴突所携带冲动的传导速度之间存在线性关系，但置信区间较宽。对于C类细胞，中枢神经突起的大小与这些神经突起所携带冲动的传导速度之间存在线性关系，但对于外周神经突起，两个异常的神经突起导致神经突起大小与传导速度之间没有相关性。对于A类细胞，中枢和外周神经突起的大小以及外周神经突起所携带冲动的传导速度与细胞体大小呈线性相关。相比之下，C类细胞则没有这种相关性。这大概意味着一个重要的差异，即细胞体的大小与A类细胞的轴突大小和冲动传导速度相关，但与C类细胞无关。一个被广泛接受的普遍观点是，大型感觉细胞产生有髓轴突，小型感觉细胞产生无髓轴突。在本研究中，有髓和无髓是根据冲动传导速度来定义的。对于那些明显较大（直径大于50微米）的细胞，其神经突起所携带冲动的传导速度总是大于2.5米/秒，而对于那些明显较小（直径小于35微米）的细胞，传导速度总是小于2.5米/秒。因此，对于这些细胞，上述普遍观点成立。然而，对于中等大小的细胞（35 - 50微米），细胞体的大小与这些神经突起所携带冲动的传导速度没有可预测的关系，因此与轴突是否有髓也没有关系。因此，上述普遍观点不适用于这一中等大小的细胞群体，而且由于这个大小范围内有许多细胞，我们认为大型细胞产生有髓轴突而小型细胞产生无髓轴突的普遍观点过于简单化。
