Effects of extensor and flexor group I afferent volleys on the excitability of individual soleus motoneurones in man

136

SUMMARY1. The possibility was investigated that interneuronal pathways contribute to I a excitation of quadriceps motoneurones in normal man. Two techniques were used: (1) the indirect spatial facilitation technique for investigating summation of Ia excitatory effects in interneurones which may be interposed in pathways to quadriceps motoneurones; (2) the post-stimulus time histogram method for time course measurement of the firing probability of voluntarily activated motor units following femoral nerve stimulation.2. The spatial facilitation technique was applied while using the quadriceps H reflex to assess the excitability of the whole motoneurone pool: the comparison was made between the excitatory effects of two conditioning stimuli applied either separately or together. Summation of effects at a premotoneuronal level is suggested if facilitation of the reflex evoked on combined conditioning stimulation is larger than the algebraic sum of facilitations evoked by separate stimuli.3. Quadriceps tendon tap and electrical stimulations applied to either the femoral nerve or to two of its branches, the nerves to the vastus lateralis and vastus medialis muscles, were used as conditioning stimuli. Since these stimuli were very weak (their strength being about at the threshold for facilitation of the test reflex), it can be assumed that they activated predominantly I a fibres.4. The facilitation of the quadriceps H reflex evoked on combined stimulation was significantly larger than the algebraic sum of facilitations evoked by separate stimuli. In many experiments, although conditioning stimuli did not evoke any reflex facilitation when applied alone, a significant facilitation appeared on combined stimulation.5. This 'extra' facilitation of the reflex on combined stimulation appeared with a central latency of 4-5 ms. It is argued that the only mechanism compatible with such a latency is summation at a premotoneuronal level.6. Post-stimulus time histograms (p.s.t.h.s) of voluntarily activated quadriceps motor units were made following femoral nerve stimulation. Stimulation was triggered at a fixed delay time after the activation of the motor unit. A special attempt was made to set this delay so that the motoneuronal after-hyperpolarization

Section: Responses Of Individualmotoneurone8mentioning

confidence: 99%

Evidence for interneuronally mediated Ia excitatory effects to human quadriceps motoneurones.

Fournier¹,

Meunier²,

Pierrot-Deseilligny³

et al. 1986

136

“…(Knox & Poppele, 1977). Assuming such a relation, others have used the integral of post-stimulus firing probability of human motor units to infer the shape of underlying p.s.p.s in motoneurones (Ashby & Labelle, 1977;Ashby & Zilm, 1978, 1982bHomma & Nakajima, 1979).…”

Section: Synaptic Potentials and Firing Probabilitymentioning

confidence: 99%

“…Our 402 SYNAPTIC POTENTIALS AND FIRING PROBABILITY observations also lend empirical support to the use ofthe integral of the post-stimulus firing probability of human motor units to estimate the initial time course of the underlying aggregate e.p.s.p.s. In active soleus motor units of human subjects, Ashby & Labelle (1977) documented post-stimulus effects produced by group I volleys in extensor muscle nerves; the duration of the primary correlogram peak (3-6 msec) was taken as a measure of the rise time of the underlying e.p.s.p. Their correlogram peaks were wider than ours, probably due to larger afferent volleys and to greater temporal dispersion of conduction in afferent and efferent pathways.…”

Section: -Correlogram Transformmentioning

confidence: 99%

Relation between shapes of post‐synaptic potentials and changes in firing probability of cat motoneurones

Fetz

Gustafsson

1983

281

228

SUMMARY1. The shapes of post-synaptic potentials (p.s.p.s) in cat motoneurones were compared with the time course of changes in firing probability during repetitive firing. Excitatory and inhibitory post-synaptic potentials (e.p.s.p.s and i.p.s.p.s) were evoked by electrical stimulation of peripheral nerve filaments. With the motoneurone quiescent, the shape of each p.s.p. was obtained by compiling post-stimulus averages of the membrane potential. Depolarizing current was then injected to evoke repetitive firing, and the post-stimulus time histogram of motoneurone spikes was obtained; this histogram reveals the primary features (peak and/or trough) of the cross-correlogram between stimulus and spike trains. The time course of the correlogram features produced by each p.s.p. was compared with the p.s.p. shape and its temporal derivative.2. E.p.s.p.s of different sizes (015--31 mV, mean 0-75 mV) and shapes were investigated. The primary correlogram peak began, on the average, 0-48 msec after onset of the e.p.s.p., and reached a maximum 0-29 msec before the summit of the e.p.s.p; in many cases the correlogram peak was followed by a trough, in which firing rate fell below base-line rate. The height of the correlogram peak with respect to base-line firing rate increased in proportion to both the amplitude of the e.p.s.p.s and the magnitude of their rising slope (in these data, amplitude and rising slope also covaried).3. The mean half-width of the correlogram peaks (065+0-28 msec (S.D.)) agreed better with the average half-width of the e.p.s.p. derivatives (0-55 + 033 msec) than

“…The effect of a particular input can be determined by constructing a histogram of the time of occurrence of motoneurone spikes following repeated presentation of a suitable stimulus. This procedure extracts from the naturally occurring spike train only those changes in firing which are time-locked to the stimulus (Moore, Segundo, Perkel & Levitan, 1970;Kranz & Corti, 1973;Kranz, Adorjani & Baumgartner, 1973;Stephens, Usherwood & Garnett, 1976;Knox, Kubota & Poppele, 1977;Ashby & Labelle, 1977). The effect of a given input is revealed in terms of the specific contribution it has made to the total firing pattern of the cell.…”

Section: Introductionmentioning

confidence: 99%

The reflex responses of single motor units in human hand muscles following muscle afferent stimulation.

Buller¹,

Garnett²,

Stephens³

1980

SUMMARY1. Changes in the probability of firing of motor units active during voluntary muscle contraction have been studied in human first and second dorsal interosseous muscles in response to muscle afferent stimulation.2. Short latency, possibly monosynaptic, excitatory responses were found in both first and second dorsal interosseous muscles following brief mechanical pulses applied to the belly of first dorsal interosseous. A second longer latency excitatory response followed the first with a mean latency of 25 msec.3. All units in both muscles showed qualitatively the same responses but units recruited at low levels of voluntary contraction strength were more responsive to muscle afferent input than units recruited at high contraction strengths. The excitatory effect of muscle afferent input within the two motoneurone pools appears to be weighted in the same way as the more complicated input associated with a gradually increasing voluntary contraction.4. These findings are discussed in relation to the relative importance of short and long latency reflex effects of muscle afferent input in the control of hand movements.