Biomedical subjects
Publications and source records attributed to B R Mackenna.
The effect of muscle temperature on the speed of contraction and on the strength of contraction of the cat jaw muscles was studied. Muscles contracted faster when their temperatures were increased. The tetanic and twitch tension decreased significantly as the animal was heated from 30 to 40 degrees C.
A gnathodynamometer was constructed to study the effect of varying the degree of jaw opening on the maximum incising forces in 20 human subjects. The incising force was greatest when the gap (distance) between the incisal edges of maxillary and mandibular incisors was 17 +/- 3 mm. We suggest that with further refinement, the measurement of the optimum distance could be used to determine the occlusal vertical dimension. The IEMG was monitored simultaneously with the incising-force measurements. No relationship was found between the maximum incising force and the IEMG at different openings of the jaws.
Perfusion of artificial CSF from a lateral ventricle to the cerebral cortical subarachnoid space in anaesthetized cats was used to study the contribution of the cerebral cortex to the concentration of 5-hydroxyindoleacetic acid (5-HIAA) in CSF. The technique did not cause rupture of the meninges. The use of [14C]5-HIAA and of probenecid suggested that there was a contribution and also a transport mechanism similar to that in the choroid plexus.
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1. The muscularis mucosae of the rabbit large intestine shows spontaneous rhythmic contractions with an average frequency of about 11/minute.2. The muscularis mucosae responds to acetylcholine, adrenaline and noradrenaline in a manner similar to that of whole segments of terminal large intestine.3. The muscularis mucosae would seem to have a cholinergic motor innervation.
1. The motility of the distal colon of the rabbit has been examined by the conventional Trendelenburg method and by an isometric, isovolumic modification of this method.2. The colon shows a range of movements, and tetrodotoxin and cold-storage have been used in an attempt to differentiate between myogenic and neurally integrated activities.3. The observable myogenic movements are pendulum movements, ;tone rings' and ;tone waves'; the last of these can be weakly propulsive. The rabbit colon also shows a neurally organized and powerfully propulsive movement which corresponds to the peristaltic wave.4. The implication of a role for nervous structures in the propulsive activity of the rabbit distal colon is at variance with the view of Lee (1960).5. The myenteric reflex arc in the colon has been examined pharmacologically. Cholinergic neural transmission has been implicated at the ganglionic-synaptic and neuroeffector junctions, but additional noncholinergic mechanisms of chemical transmission have not been excluded.
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