Onset Of Motor Activity Research Articles

Ontogeny of fetal movements in the guinea pig

Assessment of fetal motility is an approach to evaluate the development and function of the nervous system before birth. Reference values for the time of first occurrence and the incidence of normal fetal movements are indispensable for studies in which prenatal motor activity is applied as a model to study the central and peripheral nervous systems. Studies on fetal motility have been performed in a few species, particularly in the human. The aim of the present study is to describe the ontogeny of fetal motility in the guinea pig, a precocious polytocous species. After a pilot study to establish procedures for repeated ultasonographic scanning of guinea pigs, 10 domesticated animals were scanned (5.0 or 7.5 MHz convex transducer) at 2–4 day intervals between day 24 and 63 of gestation (term age 68 days). Per animal two selected fetuses were each scanned for 15 min. Images were stored on videotape and analyzed off-line for the first onset, presence and quality of fetal movement patterns, and quantity of sideway bendings, general movements, breathing movements and periods of fetal rest. Twenty-five different movement patterns could be characterized, 6 emerging at the onset of motor activity were performed only temporarily. The very first fetal movement was observed on day 24 gestational age, and subsequently most other movements developed during a period of only 5 days. Interfetal difference in onset of the frequently occurring sideway bendings, general movements, and front and hind limb movements was only 2 days. Sideway bendings and general movements co-existed during days 29 to 43. There were developmental trends in the course of pregnancy. Sideway bendings increased rapidly between 24 and 30 days and declined hereafter. General movements and fetal breathing increased during midpregnancy and declined towards parturition. Conversely, fetal rest was observed for approximately 60% of time at midgestation and a marked increase was found towards parturition. There were no significant differences in developmental trend of the various movement patterns between individual fetuses. Fetal motility in the guinea pig followed a specific temporal pattern, like in the human, but at a different time scale. The present quantitative data will enable functional investigations into the role of the neuromuscular system. They may also facilitate studies on the effect of environmental influences, such as stress, drugs, toxic substances, and food conditions, on fetal neurobehavioural development in this species.

Synchronization of an Embryonic Network of Identified Spinal Interneurons Solely by Electrical Coupling

There is a need to understand the mechanisms of neural synchronization during development because correlated rhythmic activity is thought to be critical for the establishment of proper connectivity. The relative importance of chemical and electrical synapses for synchronization of electrical activity during development is unclear. We examined the activity patterns of identified spinal neurons at the onset of motor activity in zebrafish embryos. Rhythmic activity appeared early and persisted upon blocking chemical neurotransmission but was abolished by inhibitors of gap junctions. Paired recordings revealed that active spinal neurons were electrically coupled and formed a simple network of motoneurons and a subset of interneurons. Thus, the earliest spinal central pattern generator consists of synchronously active, electrically coupled neurons.

Readiness potentials recorded from the scalp and depth leads.

Readiness potentials on voluntary hand movements were recorded from the scalp (C3, C4), premotor cortex, subcortical white matter and VL nucleus of the thalamus. Subjects were healthy right-handed men and patients with involuntary movement disorders. We obtained a slow negative shift of brain electrical potentials from the scalp and cortex preceding voluntary hand movements. The mean time interval between the onset of the readiness potential and the onset of motor activity (mean T) was 0.8 sec on right hand movements and 1.0 sec on left hand movements in healthy men. In cases with parkinsonism, the mean T value was 1.4 sec in patients with akinesia, 1.1 sec in those without akinesia. The amplitude of readiness potentials was higher in the scalp contralateral to the hand movement. The readiness potentials recorded from the VL nucleus and white matter were reversed in polarity from those of scalp and cortex. Simultaneous recordings from cortex and VL nucleus showed early onset of readiness potentials from the cortex by approximately 0.1 sec compared with the VL nucleus.

NEUROMOTOR LATENCY AND TAKE-UP OF MUSCULO- TENDINOUS SLACK AS COMPONENTS OF RT

Summary.-Neuromotor and movement larencies were recorded from the stretched and slack muscles of the preferred upper arm in G Ss. Both latencies were significantly shorter from the stretched position. Possible factors underlying this finding are discussed. The results further suggest traditional measures of may be misleading when used as indices of variations in central functioning. Smith and Whitley (1964) found that following suetching of the prime movers is significantly faster than normal RT (p. 507), in human Ss. They suggest two mechanisms which may underlie their finding, namely, when the muscle is stretched the time required to move the limb is shortened because there is less slack muscle to contract before the inertia of the limb is overcome, and that the faster is probably related to some part of the mechanism involved in neuromuscular transmission which is significantly facilitated by (p. 508). However, take-up of musculo-tendinous slack may have two components, namely, take-up due solely to stretch of the relaxed muscle and further take-up due to tension induced reflexly by the stretching of the muscle. Mark (1963) has shown slow stretch of the calf muscles in human Ss may induce reflex tension in the stretched muscle when tension is present in other areas of the skeletal musculature. R. C. Davis (1940) has shown within limits the higher the immediately preceding tension the quicker the reaction. The second component coi~ld be eliminated by training S to keep the prime movers completely relaxed until actual initiation of the movement. Adequate EMG monitoring would be essential to check on this control. Some insight into the nature of the factors underlying Smith and Whitley's results may be gained from recordings of the latency from stimulus presentation to (1) the onset of motor activity in the prime movers and (2) the movement of the limb under conditions of full extension and some degree of flexion. To this end the following investigation was performed. Preliminary evidence was also sought as to the relative significance to individual differences in RT, of what might be called mechanical factors (i.e., musculo-tendinous slack) as compared with factors of a more dynamic nature. METHOD