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Biomedical subjects

M C Brown

Publications and source records attributed to M C Brown.

At least 235 records · Page 13Linked to original sources
PubMed1973

Studies on the site of termination of static and dynamic fusimotor fibres within muscle spindles of the tenuissimus muscle of the cat.

1. The site of termination of static and dynamic fusimotor fibres has been mapped by finding which intrafusal muscle fibres have been depleted of glycogen as a result of tetanic stimulation of single gamma fibres. Long periods of stimulation coupled with occlusion of the blood supply were necessary to cause glycogen depletion.2. In cat tenuissimus muscle, dynamic gamma motor fibres always activated bag intrafusal muscle fibres, and occasionally chain fibres. Static gamma fibres always activated chain fibres and frequently activated bag fibres as well.3. It is argued that these results can be fitted into the hypothesis of the mechanism of internal functioning of the spindle originally proposed by Jansen & Matthews (1962). It is also pointed out that the results raise problems concerning the mechanism of development of the spindle motor innervation.

Action Potentials↗
PubMed1971

A comparison of the spindles in two different muscles of the frog.

1. The responses of spindles in the iliofibularis muscle of frogs to stretch during either small motor nerve fibre stimulation or the application of suxamethonium were compared.2. All spindles which were excited by small motor nerve fibre stimulation were also excited by suxamethonium, and their responses to these two methods of excitation were very similar. The drug dose was usually 5-10 mug/ml. but smaller and larger doses were effective. Large doses (> 100 mug/ml.) could sometimes lead to a reversible partial block of the spindle response to stretch.3. Suxamethonium also caused a prolonged contraction in extrafusal slow muscle fibres. This contraction was not responsible for the effect on the spindle, because the time course of its action on the muscle tension and on the spindle afferent was different.4. It was concluded that suxamethonium stimulated prolonged contraction in the small intrafusal muscle fibres, which are known to be innervated by the small motor nerve fibres.5. Only about half of the spindles in the iliofibularis muscle were excited by suxamethonium.6. In the sartorius muscle which has no slow extrafusal muscle fibres, no spindles were found to be excited by suxamethonium in the way characteristic of that due to small intrafusal muscle fibre contraction.7. It is concluded that, in frog muscles which have no slow extrafusal fibres, the muscle spindles do not have small intrafusal muscle fibres of the kind found in the iliofibularis muscle.

Animals↗
PubMed1971

The responses of frog muscle spindles and fast and slow muscle fibres to a variety of mechanical inputs.

1. The tension in the iliofibularis muscle of frogs was recorded while the muscle was stretched or released. At the same time recordings were made from single spindle afferents in dorsal root filaments. Either large or small motor nerve fibres were stimulated in split ventral root filaments.2. While small motor nerve fibres were stimulated the discharge from muscle spindle afferents was greatly increased by stretching, and greatly reduced by shortening the muscle. This sensitivity to movement was shown even if the movements were small, so that a stretch of 0.2% of the muscle length was sufficient to cause a pronounced increase in the afferent discharge.3. In contrast, during stimulation of the large motor nerve fibres the spindle was much less sensitive to movements with the result that even stretches or releases of the muscle by 1 mm did not cause very large changes in the discharge frequency.4. The tension in slow extrafusal muscle fibres in many ways mirrored the spindle discharge during the stimulation of small motor nerve fibres, for the tension was greatly increased by stretching, even through small distances, and greatly reduced by releasing the muscle. The tension in fast extrafusal muscle fibres was much less changed by such movements, and thus was rather like the spindle discharge during stimulation of large motor nerve fibres.5. As the extrafusal muscle fibres do not directly pull on and excite the spindle afferents, the simplest explanation for the similarities between the muscle tension and the spindle discharge is that the mechanical properties of the intrafusal muscle fibres innervated by the large motor nerve fibres are like those of fast extrafusal muscle fibres, and that the mechanical properties of the small intrafusal fibres are similar to those of slow extrafusal muscle fibres.6. It is shown that the cross-bridge sliding filament mechanism of muscle contraction provides a ready explanation for the differences found between fast and slow muscles, and it is concluded that a most important functional difference between the two sorts of intrafusal muscle fibres is the speed of their contractions, for it is this which determines their contrasting actions on the spindle.7. It was also found that low rates (< 4/sec) of small motor nerve fibre stimulation were often very effective in exciting the spindles. These rates produced rather little extrafusal tension.

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