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Biomedical subjects

M C Brown

Publications and source records attributed to M C Brown.

At least 253 records · Page 14Linked to original sources
PubMed1969

After-effects of fusimotor stimulation on the response of muscle spindle primary afferent endings.

1. The experiments were performed on the soleus muscle of the anaesthetized cat in which the ventral roots had been cut.2. A short period of repetitive stimulation of a single fusimotor fibre which influenced a particular spindle primary ending invariably caused a characteristic alteration in the response of the same ending to a subsequently applied ramp stretch of the muscle. The change consisted in the appearance of a burst of impulses at the beginning of the stretch where none had been present before. Occasionally, such an ;initial burst' was spontaneously present; it was then enhanced following fusimotor stimulation.3. This after-effect of fusimotor stimulation was abolished by a subsequent stretch of the muscle, but otherwise persisted for over a minute.4. When the muscle was released to below the length at which the spindle had been facilitated and a testing stretch applied from the new initial length there was no burst of impulses at the beginning of stretch. There was, however, a burst as the muscle was stretched through the length at which the fusimotor fibre had been stimulated.5. These effects are suggested to be due to the persistence of stable bonds between the actin and myosin filaments of the intrafusal fibres, so that their previously activated regions were ;stuck' at the length they were when the fusimotor stimulation was applied.6. Such effects were produced both by static and by dynamic fusimotor fibres. The effects of the two kinds of fusimotor fibre, however, appeared to be mediated by different intrafusal muscle fibres. This was shown by stimulating one kind of fibre with the muscle slightly stretched, then releasing the muscle a few mm and stimulating the other kind of fibre to the same spindle. A subsequent testing stretch then elicited two bursts, one at the beginning and one in the middle of the stretch.

Animals↗
PubMed1967

Fusimotor stimulation and the dynamic sensitivity of the secondary ending of the muscle spindle.

The response of secondary endings of de-efferented muscle spindles in the soleus muscle of the anaesthetized cat was recorded during stretching of the muscle at velocities of 5-30 mm/sec. Stimulation of single fusimotor fibres, most and probably all of which were static fusimotor fibres, produced no appreciable change in the normally small dynamic sensitivity of these endings.

Animals↗
PubMed1967

The relative sensitivity to vibration of muscle receptors of the cat.

1. Longitudinal vibration was applied to the de-efferented soleus muscle of anaesthetized cats while recording the discharge of single afferent fibres from the proprioceptors within the muscle. Conditions were defined under which vibration can be used to excite selectively the primary endings of muscle spindles without exciting the secondary endings of muscle spindles or Golgi tendon organs.2. Frequencies of vibration of 100-500 c/s were used. The maximum amplitude of vibration which the vibrator could produce fell with increasing frequency; it was 250 mu (peak to peak) for 100 c/s and 20 mu for 500 c/s.3. Primary endings of muscle spindles were very sensitive to vibration. Most could be ;driven' to discharge one impulse for each cycle of vibration over the whole of the above range of frequencies, provided the initial tension was moderate (20-200 g wt.). The amplitude of vibration required to produce driving usually varied by less than a factor of two over the whole range of frequencies. The most sensitive endings could be driven by vibrations of below 10 mu amplitude.4. Stimulation of single fusimotor fibres, whether static or dynamic fusimotor fibres, increased the sensitivity of primary endings to vibration. Contraction of the main muscle, produced by stimulating alpha motor fibres, reduced the sensitivity of primary endings even when fusimotor fibres were also being stimulated.5. The secondary endings were very insensitive to longitudinal vibration and with the amplitudes available not one of twenty-five endings could be driven at 150 c/s or above; one ending could be driven at 100 c/s by vibration of 250 mu amplitude. Stimulation of single fusimotor fibres, probably all of which were static fusimotor fibres, made them slightly more sensitive to vibration but none of them approached the sensitivity of the primary endings.6. The Golgi tendon organs were as insensitive as the secondary endings when the muscle was not contracting and none could be driven at any frequency in spite of quite high tensions in the muscle. However, when the muscle was made to contract by stimulating alpha fibres in ventral root filaments the tendon organs became appreciably more sensitive, the degree of sensitization increasing approximately with the strength of the contraction. They never became as sensitive as the primary endings, and with the amplitudes of vibration available none was driven at frequencies of over 250 c/s.7. When the amplitude of vibration was somewhat below that required to produce driving of an ending it still produced some increase in its mean frequency of discharge. However, amplitudes of vibration of 25-50 mu applied to a non-contracting muscle, whether with or without fusimotor stimulation, produced driving of nearly all primary endings without any significant increase in the mean frequency of firing of secondary endings or Golgi tendon organs. Such vibration can therefore be used as a specific stimulus for the primary endings in order to investigate the central effects or repetitive discharge of the Ia afferent fibres from them.8. Experiments on endings in the peroneus longus muscle showed that these behaved similarly to those in soleus.

Animals↗
PubMedDate not supplied

Postnatal development of the adult pattern of motor axon distribution in rat muscle.

Establishment of the adult pattern of connections between motoneurones and their muscles is known to be achieved in stages. There is an initial guidance mechanism which in higher vertebrates directs the axons with considerable accuracy to their appropriate muscles. This is followed by a stage when a large proportion of neurones die. Then, after birth, the final modifications are brought about by elimination of redundant motoneuronal branches. We present here evidence that branch elimination does not occur at random from within a motoneurone's initial intramuscular distribution, but in such a way as to sharpen the segmento-topic relationship within a muscle that motoneuronal death had earlier provided.

Aging↗
PubMedDate not supplied

An adverse interaction between warfarin and 5-fluorouracil: A case report and review of the literature.

Adverse interactions between warfarin and 5-fluorouracil (5-FU) have been reported. Such an interaction occurred in a patient with lung cancer receiving vinblastine and 5-FU. This case is the first involving a patient taking minidose warfarin for prophylaxis of catheter-associated thrombosis. Although the mechanism of the interaction is unclear, it has been postulated that 5-FU interferes with the synthesis of hepatic cytochrome P-450 2C9. Because warfarin and 5-FU are regularly coadministered, this adverse interaction might be occurring more frequently than is realized. Clinicians should be aware of this interaction and should regularly monitor the prothrombin time of patients receiving warfarin and 5-FU.

Anticoagulants↗
PubMedDate not supplied

Mesenteric vein thrombosis. Four cases and review of the literature.

Mesenteric vein thrombosis, an uncommon but important clinical entity, can cause ischemia or infarction of the small intestine. Mesenteric vein thrombosis was first described nearly a century ago, but diagnosis remains difficult because it can affect young individuals without any known predisposing disorder and because patients often present with nonspecific abdominal symptoms. We report 4 cases of small intestinal ischemia secondary to superior mesenteric vein thrombosis. Three were due to hypercoagulable states (protein-S deficiency, factor-VII abnormalities) and one was idiopathic. In recent years, the development of modern imaging techniques (particularly ultrasonography, duplex scanning, and computed tomography) have enabled early recognition of this disease. Anticoagulation is therapeutic acutely unless there are signs of peritonitis which necessitate surgical resection of the infarcted bowel.

Adult↗