Relationship among recruitment order, axonal conduction velocity, and muscle-unit properties of type-identified motor units in cat plantaris muscle.
Relationship among recruitment order, axonal conduction velocity, and muscle-unit properties of type-identified motor units in cat plantaris muscle.
复制标题
猫跖肌中类型识别的运动单位的募集顺序、轴突传导速度和肌肉单位特性之间的关系。
DOI：
10.1152/jn.1985.53.5.1303
复制
发表时间：
1985
影响因子：
2.5
通讯作者：
Faden,JS
中科院分区：
文献类型：
--
作者：
Zajac,FE;Faden,JS
对大小原理假说(37，39-41)的严格解释是，肌肉的运动单位应该按照运动神经元的大小和神经肌肉单位的大小按升序招募(有关评论，请参阅参考文献)。9、39、73)。然而，对猫后肢大型混合肌肉的研究表明，运动轴传导速度和强直性张力分别被认为是运动神经元和肌肉单位大小的指标，在快速抽动(F型)运动单位亚群(12，13，23，24，30，32，63，71，79)中，这两个指标没有相关性。为了将重点放在F型单位上，我们比较了42对猫的足底(PL)运动单位的招募顺序、轴突传导速度和强直性张力，以及与其他肌肉单位的特性。在去大脑猫完整的L7腹根细丝中，功能性地分离出单个PL-α运动轴。刺激每个分离的运动轴突所产生的张力反应被用来确定肌肉单位的强直性张力，并将肌肉单位分为S(慢抽动，耐疲劳)、FR(快抽动，耐疲劳)、FI(快抽动，中等疲劳)和FF型(快抽动，高度疲劳)。通过对轴突传导时间和长度的测量，计算每个孤立轴突的传导速度。从切断的神经丝的近端记录轴突的反射放电，并将其与同一只猫不同的、先前切断的神经丝中的另一PL轴突的放电进行比较。在同名肌肉拉伸、肌腱敲击或I组强度的单次电击对PL神经引起的反射中，每个被研究的运动单位对的招募顺序被发现。如果两个轴突中的任何一个轴突都不能放电，就像高阈值F单位的情况一样，单突触反射可以通过在PL神经的完全可逆冷却阻滞近端施加500-PPS的条件反射来促进。在所有42对研究中，较弱的运动单位具有较低的招募功能阈值。招聘也始终如一地遵循S大于FR大于FI大于FF单位的顺序。因此，具有较高抗疲劳性的一对运动单元总是具有较低的功能阈值。在包含至少一种S运动单位的22对中的21对中，具有较慢传导运动轴突的单位具有较低的招募功能阈值。
A strict interpretation of the size-principle hypothesis (37, 39-41) is that a muscle's motor units should be recruited in an ascending order according to both the size of their motoneurons and the size of their innervated muscle units (for reviews see Refs. 9, 39, 73). Studies of large mixed muscles in the cat hindlimb, however, have shown that motor axonal conduction velocity and tetanic tension, which are frequently considered indices of motoneuron and muscle-unit size, respectively, are uncorrelated in the fast-twitch (type F) motor-unit subpopulation (12, 13, 23, 24, 30, 32, 63, 71, 79). Attempting to focus on type F units, we compared the recruitment order of 42 pairs of cat plantaris (PL) motor units with both axonal conduction velocity and tetanic tension as well as with other muscle-unit properties. Single PL alpha-motor axons were functionally isolated in intact L7 ventral root filaments of decerebrate cats. Tension responses produced by stimulating each isolated motor axon were used to find the tetanic tension of the muscle unit and to classify the unit (12) as either type S (slow twitch, fatigue resistant), type FR (fast twitch, fatigue resistant), type FI (fast twitch, intermediate fatigability), or type FF (fast twitch, highly fatigable). Conduction velocity of each isolated axon was computed from measurements of axonal conduction time and length. The axon's reflex discharges were recorded from the proximal end of the cut filament and compared with the discharges of another PL axon residing in a different, previously cut filament of the same cat. The recruitment order of each motor-unit pair studied was found during reflexes elicited by homonymous muscle stretch, tendon taps, or single shocks at group I intensity to the PL nerve. If either axon of the pair failed to discharge, as often was the case with the high-threshold type F units, the monosynaptic reflex was facilitated by a 500-pps conditioning train applied proximal to a complete reversible cooling block of the PL nerve. In all 42 pairs studied, the weaker motor unit had the lower functional threshold for recruitment. Recruitment also invariably followed the order S greater than FR greater than FI greater than FF units. The motor unit of a pair with the higher resistance to fatigue thus always had the lower functional threshold. In 21 of the 22 pairs containing at least one type S motor unit, the unit with the slower-conducting motor axon had the lower functional threshold for recruitment.(ABSTRACT TRUNCATED AT 400 WORDS)