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Biomedical subjects

R M Reinking

Publications and source records attributed to R M Reinking.

At least 37 records · Page 2Linked to original sources
PubMed1983

Localization of monosynaptic Ia excitatory post-synaptic potentials in the motor nucleus of the cat biceps femoris muscle.

Evidence is presented for the existence of a localization of monosynaptic Ia excitatory post-synaptic potentials (e.p.s.p.s) in the motor nucleus of a cat hind limb muscle. Intracellular recordings from biceps femoris motoneurones were made in anaesthetized low spinal cats of the effects of stimuli to the nerve branches supplying the anterior, middle, and posterior portions of the biceps femoris muscle. Recordings were also made during stimulation of nerves to semimembranosus and semitendinosus in order to provide a means of categorizing middle biceps cells as 'extensors' (middle biceps-extensor; i.e. like anterior biceps cells) or as 'flexors' (middle biceps-flexor; like posterior biceps). Homonymous nerve-branch (i.e. from anterior, middle or posterior biceps) monosynaptic Ia e.p.s.p.s were compared within unifunctional (flexor or extensor) groups of motoneurones. In three of four comparisons (anterior biceps nerve branch onto anterior and middle biceps-extensor cells, middle biceps onto middle biceps-flexor and posterior biceps, posterior biceps onto middle biceps-flexor and posterior biceps) the anterior, middle and posterior biceps nerve branches contributed larger e.p.s.p.s to their 'own' motoneurones than to motoneurones supplying other 'compartments' of the muscle. In the fourth case, middle biceps's input appeared to have similar effects onto anterior biceps and middle biceps-extensor cells. A normalization was performed to eliminate the possibility that the differences in e.p.s.p. sizes were due to differences in cell type within the four cell groupings (i.e. differences in the number of cells supplying FF, F(int.), FR and S muscle units). This normalization confirmed that the localization in the first three comparisons was not a consequence of differences in motoneurone type and, in addition, suggested that middle biceps may indeed have greater effects on middle biceps-extensor than anterior biceps cells. In addition to the asymmetrical effects of anterior and middle biceps nerve branches onto anterior biceps and middle biceps-extensor motoneurones, it was shown that while semitendinosus and posterior biceps contributed larger e.p.s.p.s to middle biceps-flexor than to middle biceps-extensor cells, the anterior biceps nerve branch and semimembranosus nerve contributed equally to the two middle biceps groups. Analysis of cell location in the spinal cord and rostro-caudal differences in group I volley sizes gave evidence of a topographic organization of the biceps femoris motor nucleus which could contribute to the observed localization. However, localization was also evident when comparing e.p.s.p. amplitudes in pairs of neighbouring cells of different category, indicating a role for neuronal recognition factors.

Action Potentials↗
PubMed1983

Distribution of monosynaptic Ia excitatory post-synaptic potentials in the motor nucleus of the cat semitendinosus muscle.

Evidence is presented for a lack of localization of monosynaptic Ia excitatory post-synaptic potentials (e.p.s.p.s) in the motor nucleus supplying the atypical cat hind limb muscle semitendinosus, which has anatomically distinct in-series compartments. Recordings were made from dorsal root filaments containing functionally isolated Ia, spindle group II and Ib axons from the proximal and distal compartments of semitendinosus. Twitch of either of these in-series compartments resulted in accelerated discharge of Ia and spindle group II fibres in the other compartment. Ib fibres of either compartment showed an in-series response to twitch of a single compartment which was weaker than twitch of the whole muscle, a finding which was consistent with the diminished force produced by twitch of either compartment alone. In addition, intracellular recordings were made from semitendinosus motoneurones in anaesthetized low-spinal cats during electrical stimulation of the nerve branches to proximal semitendinosus and distal semitendinosus. Comparison of proximal semitendinosus and distal semitendinosus motoneurones failed to reveal any difference between the two cell groups with respect to the average Ia e.p.s.p. amplitude produced by either the proximal or distal semitendinosus nerve branch. However, e.p.s.p.s due to stimulation of distal semitendinosus were approximately 65% larger, on average, than those due to stimulation of proximal semitendinosus in either motoneurone group. Analysis of cell location along the rostro-caudal axis of the spinal cord indicated that the proximal and distal semitendinosus cell groups are largely co-extensive. Recordings of volleys in the proximal and distal semitendinosus nerve branches in response to stimulation of the L6, L7 and S1 dorsal roots showed that group I afferents from the proximal semitendinosus compartment tend to have a more rostral entry point to the spinal cord than do distal semitendinosus afferents. E.p.s.p. amplitude in either cell group due to stimulation of either nerve branch showed little dependence on cell location in the spinal cord. The results are discussed with respect to the relation between muscle function and the distribution of monosynaptic Ia connexions.

Action Potentials↗
PubMed1981

Intramuscular localization of monosynaptic Ia reflex effects in the cat biceps femoris muscle.

Intracellular recordings form biceps femoris (BF) motoneurons were made in anesthetized low spinal cats during periods of electrical stimulation of the nerve branches supplying the anterior, middle and posterior portions of the BF muscle and the nerves to semimembranosus and semitendinosus. Measurements were made of each cell's composite intrahomonymous and heteronymous monosynaptic Ia-EPSP responses to stimulation of the test nerves (branches). We have found evidence for an intramuscular localization of these monosynaptic Ia reflex effects not only when comparing responses between the two functional components of the BF muscle as is well established [6] but, in addition, when comparing responses between different parts of each functional (hip extensor and knee flexor) component as well. It is argued that both somatotopic and neuronal recognition factors may contribute to the localization of these monosynaptic reflex effects.

Animals↗
PubMed1980

A commentary on muscle unit properties in cat hindlimb muscles.

A broad survey of muscle unit properties in 14 muscles of the cat hind limb is presented which emphasizes some general features of unit properties in mammalian muscles. A more detailed analysis of muscle unit properties in three muscles of the posterior compartment of the lower leg is then presented using Burke's tetrapartite (FF, FI or F (Int.), FR, and S) unit classification scheme. Our data on the properties of motor units in cat tibialis posterior (TP) have been compared to those generated by Burke and colleagues on units in flexor digitorum longus (FDL) and medial gastrocnemius (MG). In all three muscles, twitch contraction time was distinctly slower for type S units and specific tension outputs were substantially greater for type FF units than for type S units. The innervation ratios of type FR units were slightly lower than for type S units but the specific tension of the FR units was closer to FF units than to type S units. The FF units controlled 70-74% of the cumulative force output of each muscles, indicating a substantial capacity for powerful rapid contractions of all three of these muscles despite their differences in "size," action, and force generation. Distinctive features of the three muscles included differences in the unit types' force producing capabilities and in the relative representation of "nonfatigable" type FR and S units in each muscle. In particular, TP is endowed with some unusually powerful type FF units and a high percentage (42%) of type S units. In contrast, FDL has units that develop relatively little force and an unusually high representation (56%) of type FR units. The possible relationships between these muscle features and their presumed role in posture and locomotion is discussed.

Animals↗
PubMed1980

Motor unit--muscle spindle interactions in active muscles of decerebrate cats.

Single muscle spindle afferent and motor unit EMG spike trains have been recorded simultaneously during periods of spontaneous motor activity in triceps surae muscles of decerebrate cats. The approximate time course and magnitude of the motor unit contractions were extracted from the whole muscle force record by spike-triggered averaging, and the functional interactions between motor unit contractions and spindle discharge were assessed by cross-correlating their respective spike trains. We have found that both spindle group Ia and II afferents are responsive to the contractions of single motor units in the presence of spontaneous motor activity, being strongly coupled to the activity of some motor units and indifferent to the contractions of others. Moreover, the cross-correlation analysis revealed modulation of a single motor unit's discharge pattern by the input of a single Ia afferent.

Action Potentials↗
PubMed1980

Tetrapartite classification of motor units of cat tibialis posterior.

The results of this study and its precedents suggest that the tetrapartite classification scheme might have universal applicability to at least the muscle units of cat hindlimb muscles and perhaps any mammalian muscle in which fiber typing reveals the presence of FG, FI, FOG, and type SO fibers. A possible exception to this generalization involves a small (n = 18) but thoroughly examined sample of muscle units from the first deep lumbrical muscle of the cat's foot, which led Kernell et al. (30) to conclude that the FF, FR, and S classification scheme was not directly applicable to that muscle. However, histochemical fiber typing is not yet available for that muscle. Furthermore, more extensive sampling, use of a different stimulation regime in the fatigue test, and a more detailed analysis of the sag property might well reveal that the tetrapartite classification scheme is indeed appropriate for units of cat foot muscles.

Animals↗
PubMed1976

Analysis of muscle receptor connections by spike-triggered averaging. 1. Spindle primary and tendon organ afferents.

1. The synaptic connections of 44 single identified muscle spindle Ia afferents and of 21 Golgi tendon organ (Ib) afferents from medial gastrocnemius (MG) were studied in 46 cats by the spike-triggered averaging of synaptic noise in 803 motoneurons of various types. 2. The well-known monosynaptic Ia excitatory connections were confirmed and their characteristics examined in 113 cells. The method was used at greater sensitivity than before and revealed that, in addition to the larger EPSPs of the order of 300 muV, there were many below the previously reported lower 17-muV limit. 3. By studying the Ia disynaptic inhibitory pathway with quick stretch-evoked Ia volleys and by spike-triggered averaging (STA), it was shown that the latter method can reveal disynaptic and possibly trisynaptic excitatory connections. This is believed to depend on having continuous activity in the relevant interneurons. 4. Latencies of individual connections showed broad distributions and arguments are advanced for setting working limits to mono- and disynaptic paths for Ia excitation and inhibition. Monosynaptic EPSP latency from cord entry was 0.4-1.1 ms and disynaptic inhibition was 1.2-2.4 ms. It was recognized that the boundaries are not rigid and monosynaptic Ia EPSPs may have latencies up to 1.5 ms. 5. Rise times of disynaptic PSPs were, on average, significantly longer than monosynaptic, but individual disynaptic responses could have values within the monosynaptic range. 6. A small diphasic wave shortly preceding the monosynaptic EPSPs was interpreted as a presynaptic spike. Its timing was consistent with this and, as such, permitted estimates to be made of central conduction time. 7. An early negative wave (latency less than or equal 1.1 ms) of small emplitude was sometimes detected in antagonist motoneurons when triggering from Ia afferents. It was found tha extracellular fields could be detected due to single Ia afferent excitations and efforts were made to see if the early negative wave could be explained by this. In a few cases there was evidence that a very short-latency IPSP might be occuring. This evidence and its implications are discussed with attention to the new factors which have to be considered in using the spike-triggered averaging method at very high sensitivity. 8. Ib effect were di- or trisynaptic. They were excitatory to 18% of synergists and to 28% of antagonists. They were inhibitory to 41% of synergists and to 19% of antagonists. The Ib IPSPs were larger than the EPSPs.

Animals↗
PubMed1976

Analysis of muscle receptor connections by spike-triggered averaging. 2. Spindle group II afferents.

1. The spike-triggered averaging (STA) method has been used to study synaptic connections of nine spindle group II afferents from medial gastrocnemius to 151 motoneurons of leg muscles in the cat. 2. EPSPs were found in 40 cells, predominantly of triceps surae with latency from cord entry ranging from 0.3 to 4.2 ms. Those with latency less than or equal to 1.4 ms were deduced to be monosynaptic in confirmation of Kirkwood and Sears (13). Mean amplitude for MG-LGS cells was 30.1 muV and mean rise time 1.0 ms (compared with 65.4 muV and 1.0 ms for monosynaptic Ia EPSPs from the preceding report (26)). It is argued that monosynaptic latency for spindle group II afferents could be as large as 1.65 ms. 3. The occurrence of a presynaptic spike permitted the division of EPSP latencies into central conduction time and synaptic delay components. Sindle group II central conduction times were significantly longer than those of Ia afferents, while there were no differences in the synaptic delays associated with the two afferent types. 4. EPSPs of longer latency were judged to be di- or trisynaptic. They were smaller and had longer rise times than the monosynaptic effects. Evidence is presented to show that short rise time of an individual PSP does not guarantee that it is monosynaptic. Rise times are different only on a population basis. 5. Inhibitory responses were found with latencies and mean rise times appropriate for di- and trisynaptic connections. Their mean amplitude was 4.6 muV. 6. The distribution of EPSPs and IPSPs was generally consistent with their exerting stretch reflex effects similar to that of Ia afferents and inconsistent with the inclusion of them in the grouping known as "flexor reflex afferents."

Animals↗
PubMed1975

The motor units of cat medial gastrocnemius: problem of their categorisation on the basis of mechanical properties.

The mechanical properties of 126 motor units from medial gastrocnemius muscle have been studied in 12 adult cats. Units with long contraction times (greater than 45 msec) were non fatigable (24 out of 26 units) and small (25 out of 26 units with less than or equal to 0.3% of the parent whole muscle tetanic tension) thus forming a very homogeneous population. In contrast, fast twitch units (contraction time less than or equal to 45 msec) exhibited a very broad range of tetanic tensions and fatigability. Significant correlations were found, however, within the fast contracting population which indicate a tendency for the more fatigable units to develop more tetanic tension and to be faster contracting. These findings are discussed in relation to the problems associated with using the interrelationships between twitch contraction time, tetanic tension and fatigue resistance to classify motor units into subpopulations sharing similar mechanical properties.

Animals↗
PubMed1975

The motor units of cat medial gastrocnemius: electrical and mechanical properties as a function of muscle length.

The effects of changing muscle length on the mechanical properties of 89 motor units from adult cat medial gastrocnemius have been studied in eight experiments. Few differences were found between the effects of length on tetanic tension, twitch tension, twitch-tetanus ratio, twitch contraction time, twitch half relaxation time, rate of force development and electrical activity for fast contracting (twitch contraction time less than or equal to 45 msec) and slowly contracting (greater than 45 msec) units. Those differences that did appear did not persist when these two groups were matched by tetanic tension. It is concluded that the biophysical mechanisms responsible for the changes in mechanical and electrical properties with length must be similar for fast and slow twitch units and not related to potential differences in their muscle fiber type. The effects of changing muscle length on the mechanical properties of the eight whole muscles suggest that changes in force output with length are of minor importance during normal movements as the muscle is found to be electrically active over a relatively narrow range of lengths close to the optimum length for tetanus of the whole muscle. The very shortest muscle lengths at which there is only minimal force development are not used in natural movements, while the declining limb of the length tension curve is at muscle lengths beyond the maximum in situ length.

Animals↗
PubMed1975

The tendon organs of cat medial gastrocnemius: significance of motor unit type and size for the activation of Ib afferents.

1. Histological and histochemical studies suggest that each tendon organ in a mixed mammalian muscle should be particularly responsive to the contraction of a discrete number of motor units (ca. ten to fifteen), each with differing mechanical properties. This report describes physiological experiments that demonstrate this arrangement for the tendon organs of cat medial gastrocnemius. 2. No correlations could be found between the intensity of discharge of a single tendon organ and the contraction strengths of motor units whose contraction excited the receptor. Tendon organs were found to be as responsive to contraction of small slow twitch units as they were to contraction of larger fast twitch units. Taking the data as a whole, the apparent sensitivity of the receptors during motor unit contractions (pps/force recorded at the tendon) was inversely related to the contraction strengths of the motor units. 3. These findings are discussed in relation to recent evidence on the territory of single motor units in medial gastrocnemius and the force producing capabilities of their individual muscle fibres. It is concluded that in general each motor unit, whose contraction excites a given receptor, contributes one muscle fibre to the receptor capsule. Further, it appears that the various excitatory effects of those muscle fibres inserting into a given receptor capsule are not simply related to their relative contraction strengths but also depend on the details of the mechanical coupling between each fibre and the Ib afferent receptor endings. 4. The results of an ensemble analysis show that despite the lack of correlation between the intensity of tendon organ discharge and the force developed at the tendon during contraction of different motor units, a correlation does appear when the responses of several tendon organs and the forces developed by the motor units which excite them are summed progressively. This finding has implications for the recruitment order of motor units in that the profile of the collective Ib response is shown to differ according to whether motor unit forces are summed randomly or in order of increasing contraction strengths.

Action Potentials↗
PubMed1975

Tendon organs of cat medial gastrocnemius: responses to active and passive forces as a function of muscle length.

The responses of 13 Golgi tendon organs to graded force development of 29 motor units in medial gastrocnemius of the cat have been studied in five experiments. Of the 13 tendon organs, 11 were responsive to passive stretch within the physiological range of muscle length and 5 were "spontaneously" active at very short lengths where no passive tension could be recorded. The relationship between passive force and the firing rates of the various afferents ranged from a linear one to a power relation (Y = Axb + c) with b, a widely varying exponent. Results support the general conclusion that although many Ib afferents respond to passive force within the physiological range of muscle stretch, this form of stimulus is not a particularly effective one. The statis responses of Golgi tendon organs to active force development produced by single motor units was studied at different muscle lengths. In all cases the apparent sensitivity (change in firing rate per active force developed) decreased as muscle length approached Lo. The static responses of Golgi tendon organs to force developed by single motor units were also studied during fatiguing contractions. The data suggest a sigmoid relationship between force developed at the tendon and the Ib response. The collective response of all 13 tendon organs to active and passive forces at different muscle lengths was also examined. This analysis offered further support for the viewpoint that active motor unit contractions provide themost significant excitatory input to tendon organs and that changes in passive force during muscle stretch have comparatively little effect on the collective tendon organ response. The interaction between active and passive force inputs to the Golgi tendon organs is discussed in relation to the complicated nature of the relationship between forces measured at the tendon and those acting within the receptor capsule. When these complications were taken into account it was possible to explain the differences in responsiveness of a given tendon organ to active contraction of several motor units and to passive force in terms of a single force-firing rate curve for the receptor. It is concluded that changes in the force of contraction of single motor units result in relatively small changes in Ib afferent firing and that during normal muscle contractions, changes in the number of motor units acting on a single receptor must produce far more significant changes in firing rate than changes in the amount of force developed by any single unit. Changes in dynamic Ib sensitivity to single motor unit contractions are also shown to depend on length and in a similar way to the changes in static Ib sensitivity. During fatiguing contractions, a sigmoid relation was found between the dynamic Ib response and the rate of force development by single motor units.

Animals↗
PubMed1975

Interface unit for on-line measurements of motor unit properties with a small laboratory computer.

Some simple circuitry is described which has been successfully used in conjunction with a small laboratory computer for "on-line" measurements of the force of contraction of single motor units in cat gastrocnemius and soleus muscles. Our approach emphasizes use of a sample and hold device to allow high amplification of small forces developed during single motor unit contractions which are often superimposed on relatively large whole muscle passive forces. Two digitally controlled selectable gain amplifiers are used to ensure proper modulation of the computer's ADC and to enable automatic scaling of the measured variables. An analog peak detector is incorporated into the unit such that peak force measurements can be made with the minimum of computer software. The principles governing the present design are directly applicable to the measurement of intracellularly recorded postsynaptic potentials and a variety of other physiological variables which require accurate measurement of a small transient signal superimposed on a large "control" or "resting" signal.

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