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R Granit

Publications and source records attributed to R Granit.

23 records · Page 2Linked to original sources
PubMed1966

Intracellular autogenetic effects of muscular contration on extensor motoneurones. The silent period.

1. Intracellular records have been taken from cat motoneurones belonging to gastrocnemius and soleus or to popliteal synergists during contractions of gastrocnemius and soleus, acting separately or jointly. Such contractions were elicited by brief tetani or single shocks to the peripheral end of the cut ventral roots L7 or S1.2. Hyperpolarization of the motoneurone accompanies rise of tension in contraction. The amount of it increases when at constant extension the contraction of the muscle is increased by increasing stimulus strength, as well as when it is increased by augmenting extension at constant stimulus strength. It is therefore tension-sensitive.3. The duration of the hyperpolarization induced in this manner reflects the duration of the contraction itself, being considerably longer in the slow soleus than in the faster gastrocnemius. It is often preceded by a brief wavelet of depolarization ascribed to the so-called back-response.4. Early in relaxation there occurs a transient ;hump' of membrane depolarization. This corresponds to the moment characterized by phasic bursts from the spindle primaries. The ;hump' terminates hyperpolarization.5. When the cell is stimulated by injected current to maintained repetitive firing, the ;silent period' in contraction begins with the phase of hyperpolarization and ends with the hump of depolarization as described above.6. Later during relaxation, delayed inhibition, may or may not follow often accompanied by hyperpolarizing activation noise and sometimes also visible as an extension of the silent period of a firing cell. There is, however, no marked hyperpolarization of the motoneurone in delayed inhibition.7. In the Discussion the events described above are related to previous studies employing monosynaptic testing or electromyography for the analysis of the variations of excitability caused in extensor motoneurones by autogenetic contractions as well as to known properties of stretch receptors.

Animals↗
PubMed1966

Algebraical summation in synaptic activation of motoneurones firing within the 'primary range' to injected currents.

1. In intracellular studies of cat lumbar motoneurones constant synaptic stimuli such as stretch, contraction or a high-frequency stimulation of a cut afferent nerve have been superimposed on firing in response to injected currents.2. As long as the slope relating spike frequency to injected current remained constant, which by definition is the ;primary range' of firing, algebraical summation of superimposed synaptic stimulation prevailed. Added quantities in these experiments were then between 2.0 and 56.2 impulses/sec for excitation, between -2.8 and -21.8 impulses/sec for inhibition.3. Data were obtained correlating firing rates with amount of synaptic potential and current respectively.4. Theoretical implications are dealt with in the Discussion.

Animals↗
PubMed1966

Synaptic stimulation superimposed on motoneurones firing in the 'secondary range' to injected current.

1. This paper extends the work on the ;primary range' of firing (Granit, Kernell & Lamarre, 1966), in lumbar motoneurones to the ;secondary range'. By definition the latter begins when, with stronger currents, the linear curve relating firing rate to injected current in the primary range undergoes a fairly sudden increase of slope.2. It was shown that motoneurones firing at the higher frequencies of the secondary range were partially inactivated. Yet such firing rates were within the physiological range.3. Algebraical summation of firing rates, when present in the secondary range, implied at the same time that the synaptic amount added was diminished by comparison with what it had been within the primary range.4. Superimposed synaptic excitatory stimuli did not (as in the ;primary range') regularly add their effect algebraically on to the rate of firing achieved by injected currents alone. More commonly the synaptic effect of the constant input underwent a progressive increase throughout the secondary range.5. Superimposed inhibitory stimuli regularly reduced the slope constant as determined by trans-membrane current alone and, by counter-acting inactivation, made the motoneurone approach the mode of firing characteristic of the ;primary range'.6. The latter finding emphasizes the significance of analysing firing motoneurones with the aid of ;slope constants' and provides inhibition with a new role in the integrative behaviour of motoneurones, as considered in the Discussion.

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