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R M Ridge

Publications and source records attributed to R M Ridge.

33 records · Page 2Linked to original sources
PubMed1978

Properties of twitch motor units in snake costocutaneous muscle.

1. Single motor units of twitch muscle fibres were studied in isolated nerve-muscle preparations of m. costocutanei inferiores from grass and garter snakes. Preparations were superfused with Ringer solution at a controlled temperature of 22 degrees C.2. The peak and time-to-peak tension (contraction time) were measured for isometric twitches of forty-seven whole muscles and 83 motor units. The sample of motor units was drawn from an estimated total population of 213-355 twitch units. Peak tetanic tensions were also measured. The measurements were made at muscle lengths at which the twitch tension was maximal, and this length was not always the same for whole muscle and unit twitches. In fifty-nine cases 1 and in twelve cases 2 motor units were isolated from each muscle.3. Whole muscle contraction times ranged from 22-61 msec (mean +/- S.D. = 40.3 +/- 9.8 msec) and those for units from 18-92 msec (mean +/- S.D. = 46.9 +/- 15.9 msec). The wide range for whole muscles is discussed.4. The percentage of the whole muscle tetanic tension contributed by each unit (unit size) was calculated. Contraction time was inversely related to unit size.5. Twitch-tetanus ratios were calculated and found not to be related to unit contraction time.6. The conduction velocities of axons innervating 23 motor units were calculated from latency measurements at two points along the length of the nerve. They ranged from 1.9 to 10.4 m/sec. Axon conduction velocity was inversely related to unit contraction time, and directly related to unit size.

Action Potentials↗
PubMed1978

Post-tetanic potentiation of twitch motor units in snake costocutaneous muscle.

1. Isometric twitch responses of single motor units in snake costocutaneous muscle have been recorded before and after conditioning tetanic stimulation. 2. Most units showed post-tetanic potentiation of twitch tension, associated with increased maximal rate of rise of twitch tension, and in some cases also associated with prolongation of twitch contraction time. A few units showed a short phase of actual depression of the post-tetanic twich responses, followed by potentiation. 3. The time course and magnitude of post-tetanic changes of twitch tension and maximal rate of rise of tension could be described by the sum of three processes which are assumed to be maximal close to the end of the conditioning tetanus: (i) a rapidly declining potentiation (called here early potentiation, which lasted less than 2 sec) which may have a purely mechanical origin; (ii) a much slower-declining potentiation (called here prolonged potentiation, which lasted up to 15 min); and (iii) a process which lasted up to 60 sec during which twitch potentiation was reduced. The latter process (called here depressed potentiation) was usually apparent as a marked trough in the plots of twitch amplitude versus time after the conditioning tetanus, and occassionally was evident as an actual transient depression of twitch amplitude after the tetanus compared with that before. 4. The effects of the prolonged potentiation and the depressed potentiation on the maximal effect of each process close to the end of the tetanus were extracted by fitting single exponential equations to different portions of the data, using a computer program. 5. Twitch potentiation associated with increased maximal rate of rise of tension seemed to be a separate phenomenon to that associated with prolongation of contraction time, seen when conditioning tetani of higher frequency and numbers of stimuli were employed. The depressed potentiation of twitch tension tended to be partly masked in cases where contraction time was prolonged, but this did not affect the depressed potentiation of maximal rate of rise of tension. 6. The post-tetanic potentiation shown by a unit was related to the contraction time of the unit, in addition to the well known relationship to the initial twitch-tetanus ratio. The depressed potentiation may correlat more closely with the initial twitch-tetanus ratio than with the unit contraction time. 7. The magnitude of maximal depressed potentiation shown by a unit may be directly correlated to that of maximal prolonged potentiation. 8. The time constant of decay for prolonged potentiation of twitch tension tended to be related inversely to unit contraction time and directly to unit size and the maximal value of prolonged potentiation oftwitch tension. The time constant of decay for prolonged potentiation of maximal rate of rise of tension tended to be related to unit size and initial twitch-tetanus ratio, and the time constant of decay for depressed potentiation of rate of rise of tension tended to be related to unit size. 9...

Action Potentials↗
PubMed1976

Stretch receptors in urodele limb muscles.

Non-encapsulated, fine beaded nerve endings were found histologically on some muscle fibres in a number of limb muscles in newts and axolotls. They were present in newt muscles that had been chronically de-efferented, and in which no efferent activity survived, and were therefore likely to be sensory. They were located only on muscle fibres on or near the outside surface of the muscle. These small-diameter muscle fibres were characterised histochemically by low lipid, SDH and phosphorylase content; ultrastructurally by low glycogen content, and relatively large myofilaments poorly delimited by a sparse SR. There were many of this type (Type 1) that did not support sensory endings. A few endings occurred on another larger-diameter type of fibre (Type 2) whose properties were opposite to those listed above for Type 1. There was virtually no specialization of muscle fibre structure beneath the sensory endings. Physiological experiments involving ramp-and-hold and sinusoidal stretch applied to the muscle whilst recording single-unit afferent responses in m.ext. dig. III of axolotls showed unit responses very similar to those known from muscle spindles, particularly those of the frog.

Action Potentials↗
PubMed1973

Innervation of extrafusal and intrafusal fibres in snake muscle.

1. Intrafusal fibres of snake receive motor supply from branches of axons innervating extrafusal motor units. By intramuscular stimulation of motor units by single shocks, and critical curarization of the muscle, we have identified at least some of the motor units contributing motor supply to individual intrafusal fibres. Intrafusal fibre activation was observed by visual examination of the contracting intrafusal fibre, and by recording the resulting spindle afferent discharge.2. The main finding is that in some cases the motor supply to one intrafusal fibre comes from more than one motor unit. The contributing motor units may be either dissimilar twitch units, or twitch and tonic units. Thus some of the intrafusal fibres studied showed polyneuronal motor innervation of heterogeneous origin.3. In critically curarized muscle, the time course of a spindle afferent discharge, following single-shock stimulation of a motor unit contributing motor supply to the intrafusal fibre, showed little variation with the type of motor unit being stimulated.4. The response of each spindle to a standard stretch was recorded. There was no correlation between dynamic index and type of motor unit or units contributing motor supply. However, the method limits the value of negative findings, and this is discussed.5. The contraction times and tensions of a sample of motor unit isometric twitches are described.

Action Potentials↗
PubMed1971

Different types of extrafusal muscle fibres in snake costocutaneous muscles.

1. Tonic and twitch muscle fibres were identified physiologically in m. costocutanei superiores and inferiores of garter snakes and grass snakes.2. Tonic fibres were multiterminally innervated and showed s.j.p.s in response to nerve stimulation. They did not show propagated A.P.s. They were innervated by motor axons with lower conduction velocities than those to twitch fibres, and often gave a contraction and developed tension in response to a single shock to the nerve. Intracellular square pulse analysis showed that C(m) = 1 muF/cm(2) and R(m) = 40,000 Omega cm(2).3. Twitch fibres showed a conducted action potential in response to nerve stimulation, and focal, as opposed to diffuse, innervation. They showed a variety of isometric twitch contraction times (times-to-peak of about 30-65 msec). Groups of similar motor units contained fibres of approximately similar contraction times. Slow twitch (and tonic) fibres often appeared silvery under dark field illumination, while faster twitch fibres appeared clear. No difference in C(m), R(m) or lambda was found between faster and slow twitch fibres. Values were approximately 3-4 muF/cm(2), 3000-4000 Omega cm(2) and 2 mm respectively.

Action Potentials↗