Modulation of slow and fast elbow extensor EMG tonic activity by stretch reflexes in man

Reflex EMG responses to sudden passive flexion of the elbow were recorded from anconeus and triceps brachii in 5 human volunteers. While the subjects were required not to resist the flexion movement, they were required to maintain an extension torque of 3.5 or 7.0 Nm prior to its onset. Under these isotonic conditions, the latency and amplitude of the reflex activities from anconeus and triceps brachii did not differ significantly, in contrast to the findings of Le Bozec (1986) in actively relaxed subjects. The myotatic/postmyotatic EMG amplitude ratio did not provide a further quantitative way to distinguish between these muscles. The absence of a difference between the reflex activities of a slow (anconeus) and a fast (triceps brachii) muscle is interpreted as resulting from a strong drive of spindle activity on the whole extensor motoneuron pool, which outweights the differences in recruitment due to the differing relative amounts of type I and type II fibres in the two muscles. Differences like those described between finger and calf muscles by other authors are thought to be due to the relative degree of corticalization of these muscles. All short and long latency responses of the muscles increased in magnitude and decreased in latency with increasing background EMG activity as well as with increasing initial length. The position and tonic activity dependency of these responses is explained in terms of alpha-gamma coactivation.     

Collagen gene construction and evolution

Summary Collagen genes appear to have been assembled by the tandem repetition of homologous primary (9 base pair), secondary (54 base pair), and tertiary (702 base pair) modules. In vertebrate interstitial collagen genes many of the secondary modules are separated by introns, but in invertebrate collagen genes the non-coding sequences lie near the ends of supposed tertiary modules and are therefore about 702 (54×13) base pairs apart. The genes for vertebrate interstitial collagens (types I–III) seem to have been constructed by the tandem repetition of five tertiary modules, three of which were subsequently shortened by internal deletions. This shortening of the gene resulted in the non-integral relationship between the period of the fibrils and the length of the molecules of vertebrate collagens, and was therefore responsible for the mechanical properties of the completed product. Comparisons of the amino acid sequences of various collagens indicate that the main types of collagen evolved about 800–900 million years ago, a date that agrees well with the fossil record of primitive Metazoa.     

Naloxone influences ultrasonic calling in young mice

The ultrasonic calls produced by three day old mice when separated from the nest mother and siblings increase in number when naloxone is injected.