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Biomedical subjects

E Godaux

Publications and source records attributed to E Godaux.

At least 19 recordsLinked to original sources
PubMed1979

Voluntary motor commands in human ballistic movements.

The integrated electromyogram of the first dorsal interosseous muscle in normal humans presents a brief early burst in voluntary ballistic abduction of the index finger. Unexpected decrease in torque load does not change the burst. By contrast, in fast ramp abduction with a time-to-peak of 0.5 second, the electromyographic activity is fairly continuous up to the peak displacement, and it is silenced with a delay of 50 msec by unexpected unloading. Thus fast ramp, but not ballistic, voluntary contractions are under current long loop control from proprioceptive input. In a second set of experiments, the analysis of single motor unit potentials with highly selective electrodes in interosseous muscle indicated that ballistic thresholds are smaller than ramp thresholds under either isotonic or isometric conditions. However, the recruitment rank of the motor units was identical in finger abductions carried out in either ramp or ballistic modes.

Adult↗
PubMed1978

Ballistic contractions in fast or slow human muscles: discharge patterns of single motor units.

1. Single motor units were recorded from the masseter, soleus and first dorsal interosseous muscles of normal adult man. An analysis of discharge patterns was carried out either during slow ramp voluntary contractions, or during self-initiated isolated ballistic voluntary contractions. The isometric myogram was simultaneously recorded.2. Each motor unit was only recruited when the peak force of a brisk contraction exceeded a certain value and a ;ballistic force threshold' (in kg) was estimated for the unit from a large series of brisk contractions of different strengths. For each muscle, the ranking order for recruitment of different motor units recorded from one electrode position was virtually identical in slow ramp versus brisk ballistic contractions of different force (Kendall rank correlation coefficient = 0.91-1.0). There was no evidence for any consistent selective activation of fast twitch motor units in ballistic contractions.3. The ballistic force threshold is considerably reduced with respect to the slow ramp force threshold for the motor units of the soleus muscle. This drop is also marked for the units of the first interosseous and tibialis anterior muscles, whereas it is only small for the units of the masseter muscle. These data have been validated after consideration of the complicating factor related to the possible differential involvement of synergic muscles in ramp or ballistic contractions.4. In the masseter and first interosseous muscles, the time to peak is about 80 msec in small ballistic voluntary contractions and it increases to about 150 msec in strong contractions. This effect appears related to repetitive discharges of single motor units when their force threshold is exceeded. By contrast, in the soleus muscle, the time to peak remains at about 150 msec both in small and in strong ballistic contractions and most soleus motor units fire only one spike in the ballistic burst.5. Brisk ballistic contractions are graded in force by the recruitment of additional motor units according to their usual rank order. The importance of rate gradation through the repetitive firing of motor units varies in the different human muscles investigated, being quite significant in isometric brisk contractions of the masseter and first interosseous muscles but much less so in the soleus muscle in which little repetitive firing of single motor units was observed over the range of ballistic forces studied.

Action Potentials↗
PubMed1978

Mechanism of the vibration paradox: excitatory and inhibitory effects of tendon vibration on single soleus muscle motor units in man.

1. The parameters of presynaptic inhibition of the Ia spindle afferents from soleus muscle by vibration have been investigated. The inhibitory effects increase with the amplitude of vibration, but decrease when the vibration frequency is increased.2. The monosynaptic reflex threshold of twenty-one single soleus motor units activated in the H (Hoffmann) reflex by a single electrical stimulus to the posterior tibial nerve was estimated quantitatively and expressed in relation to the size of the simultaneously recorded H reflex.3. A parametric study of the effects of various Achilles tendon vibrations on the reflex threshold of the single soleus motor units indicated that their order of derecruitment is concordant with their rank order for activation in the phasic reflexes of the soleus. The last recruited motoneurones are the most susceptible to being silenced by steady vibration.4. Muscle vibration progressively recruits single motor units according to the motoneurone size principle through polysynaptic proprioceptive pathways. However the presynaptic inhibition of Ia spindle afferents simultaneously induced by the vibration works in reverse on the same rank order of motoneurones of the soleus spinal pool, thereby limiting the polysynaptic recruitment of units in the tonic vibration reflex while depressing the autogenic phasic proprioceptive reflexes. These mechanisms elucidate the so-called vibration paradox and extend the size principle of Henneman to presynaptic inhibitory effects.

Achilles Tendon↗
PubMed1977

Ballistic contractions in man: characteristic recruitment pattern of single motor units of the tibialis anterior muscle.

1. Single motor units were recorded with highly selective electrodes from intact tibialis anterior muscle in the adult man. A detailed parametric analysis was made of the discharge patterns during voluntary isometric contractions of different peak forces carried out at various rates of force development. 2. During the smooth tracking of a ramp force, the different motor units recorded from a given muscle site were recruited in a consistant order, each unit becoming active when the muscle developed a certain level of force. The threshold of some of the units in such slow ramp contractions exceeded 8 kg. By contrast, in brisk ballistic contractions reaching a peak force of 12 kg in less than 0-15 sec, the same motor units discharged in a transient burst which largely preceded the muscle force production. 3. In slow tracking ramp contractions, the instantaneous frequency of single motor units was initially rather low (5-15/sec) and it increased as the ramp force augmented. By contrast, in (strong) ballistic contractions, the same units discharged at an unusually high instantaneous frequency (60-120/sec) early in the burst and the firing frequency decreased thereafter. Such hitherto unknown pattern appears characteristic of ballistic contractions and it was not found in even fast tracking ramp contractions achieving 12 kg in only 0-4 sec. 4. The potentials of the different motor units activated are rather crowded at intervals of a few msec in the early burst of a strong ballistic contraction and observations on the rank activation of the different motor units do not provide reliable data for the analysis of the recruitment order of units in ballistic contractions. 5. A new method is described for estimating ballistic force threshold of single motor units. When a large series of brisk ballistic contractions with peak forces ranging from 0-05 to 12 kg was carried out any given motor unit only became active when the ballistic peak force exceeded a certain reproducible value. A detailed analysis of the recruitment order based on these ballistic force thresholds showed it to be virtually identical to the recruitment order of the same units in slow tracking ramp contractions (correlation=0-95). 6. Ballistic contractions are graded in force both by the recruitment of additional motor units in stronger contractions, and by an increase in their rate of firing. These gradation mechanisms are discussed.

Action Potentials↗
PubMed1976

Habituation of exteroceptive suppression and of exteroceptive reflexes in man as influenced by voluntary contraction.

Habituation kinetics were found to vary considerably in different polysynaptic pathways of the brain stem in man. The exteroceptive reflex of the digastric muscle habituates markedly, even for stimuli repeated at 1-min intervals. The second component of the blink reflex habituates for intervals below about 8 sec, but this can largely be prevented by steady voluntary contraction of the muscle. On the other hand the exteroceptive suppressions of the masseter muscle only disclose slight habitaution of their late component ES2 and no habituation of the early component ES1. This does not appear to be affected by voluntary activation since the suppressive effects present the same pattern in relaxed masseter muscles tested by proprioceptive reflex activation. Exteroceptive reflexes and exteroceptive suppressions of similar latencies disclose genuine and important differences in their habituation kinetics.

Adult↗
PubMed1975

Exteroceptive suppression and motor control of the masseter and temporalis muscles in normal man.

Single electrical stimuli to the gums and mucosa inside the mouth elicit two successive exteroceptive suppressions (ES1 and ES2) in the voluntary electromyogram of the masseter and temporalis muscles in normal man. The same afferent axons appear to be involved in the two effects, as indicated by the intensity function, the electrical excitability, the afferent conduction velocity and the lack of differential effect of Xylocaine infiltration of the inferior alveolar nerve. Two similar phases of inhibition involve the monosynaptic masseter reflex and the synchronized electromyographical spikes induced by jaw vibration. Exteroceptive suppression is thought to be mediated, in the brain stem, by both an oligosynaptic (ES1) and a multisynaptic (ES2) mechanism.

Action Potentials↗
PubMed1975

Human masseter muscle: H- and tendon reflexes. Their paradoxical potentiation by muscle vibration.

We developed a method for direct electrical stimulation of the masseter nerve in man. Both direct M-reponses and genuine H-reflexes were recorded from the ipsilateral masseter muscle. Muscle vibration that inhibits the Achilles tendon reflex and the soleus H-reflex was found to potentiate the masseter tendon reflex and also the masseter H-reflex. This unexpected contrast may be related to peculiar brain stem circuitry of the masseter reflex mechanism.

Achilles Tendon↗
PubMed1975

Vibration-induced discharge patterns of single motor units in the masseter muscle in man.

Single motor unit potentials were recorded with small bipolar wires from intact masseter muscles in the adult man and a detailed parametric analysis of the effects of muscle vibration on motor unit discharges was carried out. 2. When the vibration amplitude was kept constant, each unit started firing at a definite threshold of vibration frequency. With higher frequencies the rate of firing rapidly reached a maximum. Units recruited at higher frequencies presented a lower maximum rate of firing. 3. When the vibration frequency was kept constant, each masseter unit discharged at a definite threshold of vibration amplitude. With higher amplitudes the unit quickly reached a maximum rate of discharge. Units with a higher frequency threshold tended to also present a higher amplitude threshold. Motor unit "excitability" curves could be plotted using the combined threshold conditions for frequency and amplitude of applied vibrations. 4. With a given parametric set of vibration, the units only started firing at a given delay after the onset of vibration. The delay was quite different for different units and it increased considerably, sometimes by several seconds, when the vibration amplitude was made smaller. 5. In all the experimental conditions tested, and even when the unit discharge did not start until several seconds after vibration onset, the unit potential presented a close and highly consistent temporal relation to the vibration cycles. The slow recruitment process is thought to involve a polysynaptic excitatory mechanism which progressively depolarizes the masseter motoneurones close to their threshold, the actual firing being triggered by monosynaptic excitatory post-synaptic potentials from I(a) afferents, hence the small latency jitter recorded. This special pattern of tonic vibration reflex in jaw-closing muscles in man may result from the lack of reciprocal inhibition from the jaw-opening muscles.

Action Potentials↗
PubMed1975

Evidence for a monosynaptic mechanism in the tonic vibration reflex of the human masseter muscle.

Vibration of the masseter and temporalis muscles in normal human adult subjects elicits a tonic vibration reflex with unexpected features. The electromyographic response is not asynchronous as in the limb muscles, but involves well-defined spikes with a one-to-one temporal relation to the vibration cycles. The effect of various parameters such as muscle stretch, vibration frequency or amplitude, etc, has been investigated. The small latency fluctuation of the vibration-induced spikes is compatible with a monosynaptic reflex mechanism which is considered to be assisted by a polysynaptic facilitatory background of proprioceptive origin.

Adult↗