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Biomedical subjects

J C Luck

Publications and source records attributed to J C Luck.

71 records · Page 4Linked to original sources
PubMed1974

Post-tetanic effects in motor units of fast and slow twitch muscle of the cat.

1. Motor unit twitches were examined in cat flexor digitorum longus (fast twitch) and soleus (slow twitch) muscles. The time course of the effects of a standard tetanus on the peak twitch tension was plotted and the maximal potentiation or depression (the post-tetanic ratio) was measured.2. The post-tetanic ratio decreased continuously as the twitch time to peak of motor units increased; motor units from flexor digitorum longus and soleus could be described as a single population. The closest approximation to a linear relationship was found by plotting post-tetanic ratio against the reciprocal of time to peak.3. The post-tetanic ratio was also related to the ratio of tetanic to twitch tension. The time of maximum potentiation or depression occurred between 1 and 11 sec, but this variable was unrelated to the time to peak or any other characteristic of the motor unit.

Animals↗
PubMed1973

Isometric contractions of motor units in a fast twitch muscle of the cat.

1. Isosmetric contractions of cat flexor digitorum longus whole muscles and of functionally isolated motor units have been measured under conditions similar to those used by Buller & Lewis (1965a).2. Motor unit twitch time to peak was inversely related to axonal conduction velocity. The logarithm of tetanic tension was directly related to conduction velocity. These relationships suggest that each motoneurone has an influence on the muscle fibres which it innervates.3. The ratio of twitch to tetanic tension was directly related to the time to peak of the motor unit. This fact might be explained by variation between motor units of the duration of ;active state'.4. The muscle length at which tension was maximal varied between motor units and the optima were found over the range of muscle lengths which could occur in the body. Slow motor units had longer optimal lengths.5. The sample of motor units was considered to be unbiased because the distribution of axon conduction velocities was compatible with reported motor fibre diameter spectra of the muscle nerve. The mean motor unit tetanic tension gave a reasonable estimate of the number of alpha-motor axons in the muscle nerve. Twitch tensions gave a value that was 40% higher.6. Motor unit and whole muscle data were in good agreement for length-tetanus tension curves, for times to peak and for twitch-tetanus ratios at long muscle lengths.

Action Potentials↗
PubMed1970

Afferent vagal fibres with an expiratory discharge in the rabbit.

1. An investigation was undertaken in the spontaneously breathing, anaesthetized rabbit to observe the response of vagal sensory endings to inflation and deflation stimuli which were sufficient to produce Hering-Breuer reflexes.2. When artificial changes in lung volume were produced by applying step changes in intratracheal pressure, activity in pulmonary stretch receptors increased with inflation and decreased with deflation.3. A small number of vagal afferent fibres were encountered which exhibited a discharge with a respiratory modulation consisting of an increase in activity during the phase of expiration. This pattern of discharge was accentuated when the animal was artificially ventilated with the chest either open or closed.4. These expiratory receptors were stimulated by step changes in intratracheal pressure of -5 and +15 mm Hg to produce a high frequency, slowly adapting discharge which persisted for the 10 sec period of the pressure application. The endings were localized in the extrapulmonary bronchi and lung parenchyma and the afferent fibres were myelinated with conduction velocities of 10.6-29.5 m/sec.5. The pronounced effect of deflation stimuli on the endings indicates that they probably act as one of the afferent mechanisms in the Hering-Breuer deflation reflex.

Animals↗