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Biomedical subjects

J A Stephens

Publications and source records attributed to J A Stephens.

At least 73 records · Page 4Linked to original sources
PubMed1978

The projection of jaw elevator muscle spindle afferents to fifth nerve motoneurones in the cat.

1. By spike-triggered averaging of intracellular synaptic noise it has been shown in pentobarbitone anaesthetized cats that jaw elevator muscle spindle afferents with their cell bodies in the mid-brain have a relatively weak monosynaptic projection to masseter and temporalis motoneurones. 2. Extending the spike-triggered averaging method to recording extracellular excitatory field potentials it has been shown that virtually all the spindles do project monosynaptically to the motoneurone pool. It is concluded that the general weakness of the projection is due to its restriction to a small proportion of the motoneurones, possibly those concerned most with tonic postural functions. 3. The shape of individual intracellular e.p.s.p.s together with the spatial distribution of extracellular excitatory potential fields provide some evidence for a dentrically weighted distribution of the synapses. 4. Evidence is presented that both primary- and secondary-type spindle afferents project monosynaptically, the secondary effects being some 71% of the strength of the primary ones.

Action Potentials↗
PubMed1977

The mechanical properties of human motor units with special reference to their fatiguability and recruitment threshold.

The recruitment thresholds, twitch tension, twitch contraction time and fatiguability of human motor units have been studied in the first dorsal interosseous of the hand. Units recruited at contraction strengths less than 50 g had relatively low twitch tensions (0.18-1.9 g), long contraction times (59-146 msec) and were non-fatiguable. Units recruited at higher contraction strengths (less than 200 g) had higher twitch tensions (15-26g), faster contraction times (33-57 msec) and were highly fatiguable. It is concluded that during graded voluntary muscle contractions motor units are recruited in order of increasing contraction strength and diminishing fatigue resistance.

Adolescent↗