Intramuscular and epimuscular microstimulation of single motor units

Abstract

191 SUMMARYA new ep!muscular method for stimulating single motor units (m.u.'s) in free prepared muscle is described. Unit isolation is stable and can be continued for long periods. The method is compared with an intramuscular stimulation technique and histological evidence is presented to confirm the validity of both techniques.Conventional methods for stimulation of individual motor-units {m.u.'s), i.e. stimulation of a.motoneuron or isolated ventral roots, are time-consuming and technically demanding. Mczeover such niethods are not suitable for human muscles. Buchthal et al.[1] stimulated in human muscle 'bundles of muscle fibres' with intramuscular electrodes. Several investigators [ 7,10--12 ] showed that such intramuscular stimulation may excite fine motor nerve twigs, which may lead to contraction of single m.u.'s.In this paper we will: (i) describe the difficulties involved in intramuscular stimulation of small musclm (EDL and soleus of rat); (fi) introduce 'epimuscul~ stimulation' to overcome these difficulties; (ifl) provide histological confirmation of the validity of both iutra-and epimuscular methods for single unit stimulation; (iv) ~ their limitations. The criterion we used ~~t all-or-nothing force and EMG adjured Close to the threshold value(1). ~ce our ex~" n~ dmmmd long term stable simulation of the same m:a.a second critmion~wmin~oduced, i.e. unvarying force and EMG reswhen ~ ~ ~al ~hbld stimulus amplitude (II), which

The different intracellular action potentials of fast and slow muscle fibres

“…The muscle was in vivo as described before . Single motor units were stimulated with the epimuscular stimulation method of Griep et al (1980). The body temperature of the rat and of the muscle were controlled and regularly checked.…”

Calculation and registration of the same motor unit action potential

“…This time is composed of the time needed for conduction along the nerve twigs and the endplate delay time. For the EDL muscle the mean interval was approximately 0.4 msec (Griep et al 1980, Fig. 2).…”

“…Griep et al {1980) showed clearly that this method of stimulation (the so-called epimuscular microstimulation) triggers a single motor unit via excitation of an axon terminal.…”

“…These false fibres were eliminated from the MUAP calculation. According to Griep et al (1980) only one motor unit was stimulated: the motor unit force decreased smoothly and the MUAP shape changed gradually.…”

In vivo magnetic and electric recordings from nerve bundles and single motor units in mammalian skeletal muscle. Correlations with muscle force.

“…All experiments were carried out at the optimal twitch length of the whole muscle (Wallinga-de Jonge, Boom, Boon, Griep, and Lammeree, 1980). The whole muscle twitch was generated by means of supramaximal stimulation of the common peroneal nerve, which was immersed in a small saline pool surrounded by muscles in the thigh.…”